JSON-LD 1.1 Processing Algorithms and API

Final Community Group Report

Latest editor's draft:
https://json-ld.org/spec/latest/json-ld-api/
Test suite:
https://json-ld.org/test-suite/
Previous version:
https://www.w3.org/TR/2014/REC-json-ld-api-20140116/
Editor:
Gregg Kellogg (Spec-Ops) (v1.0 and v1.1)
Former editors:
Markus Lanthaler (Graz University of Technology) (v1.0)
Manu Sporny (Digital Bazaar) (v1.0)
Authors:
Dave Longley (Digital Bazaar) (v1.0)
Gregg Kellogg (Spec-Ops) (v1.0 and v1.1)
Markus Lanthaler (Graz University of Technology) (v1.0)
Manu Sporny (Digital Bazaar) (v1.0)
Niklas Lindström (v1.0)
Participate:
GitHub json-ld/json-ld.org
File a bug
Commit history
Pull requests

Abstract

This specification defines a set of algorithms for programmatic transformations of JSON-LD documents. Restructuring data according to the defined transformations often dramatically simplifies its usage. Furthermore, this document proposes an Application Programming Interface (API) for developers implementing the specified algorithms.

Status of This Document

This specification was published by the JSON for Linking Data W3C Community Group. It is not a W3C Standard nor is it on the W3C Standards Track. Please note that under the W3C Community Final Specification Agreement (FSA) other conditions apply. Learn more about W3C Community and Business Groups.

This document has been developed by the JSON for Linking Data W3C Community Group as an update to the 1.0 recommendation [JSON-LD-API] developed by the RDF Working Group. The specification has undergone significant development, review, and changes during the course of several years.

There are several independent interoperable implementations of this specification, a test suite [JSON-LD-TESTS] and a live JSON-LD playground that is capable of demonstrating the features described in this document.

If you wish to make comments regarding this document, please send them to public-linked-json@w3.org (subscribe, archives).

Set of Documents

This document is one of three JSON-LD 1.1 Recommendations produced by the JSON for Linking Data W3C Community Group:

1. Introduction §

This section is non-normative.

This document is a detailed specification of the JSON-LD processing algorithms. The document is primarily intended for the following audiences:

To understand the basics in this specification you must first be familiar with JSON, which is detailed in [RFC7159]. You must also understand the JSON-LD syntax defined in the JSON-LD 1.1 Syntax specification [JSON-LD11CG], which is the base syntax used by all of the algorithms in this document. To understand the API and how it is intended to operate in a programming environment, it is useful to have working knowledge of the JavaScript programming language [ECMASCRIPT-6.0] and WebIDL [WEBIDL]. To understand how JSON-LD maps to RDF, it is helpful to be familiar with the basic RDF concepts [RDF11-CONCEPTS].

1.1 Contributing §

There are a number of ways that one may participate in the development of this specification:

1.2 Terminology §

This document uses the following terms as defined in JSON [RFC7159]. Refer to the JSON Grammar section in [RFC7159] for formal definitions.

array
In the JSON serialization, an array structure is represented as square brackets surrounding zero or more values. Values are separated by commas. In the internal representation, an array is an ordered collection of zero or more values. While JSON-LD uses the same array representation as JSON, the collection is unordered by default. While order is preserved in regular JSON arrays, it is not in regular JSON-LD arrays unless specifically defined (see Sets and Lists in the JSON-LD Syntax specification [JSON-LD11CG]).
JSON object
In the JSON serialization, an object structure is represented as a pair of curly brackets surrounding zero or more key-value pairs. A key is a string. A single colon comes after each key, separating the key from the value. A single comma separates a value from a following key. In JSON-LD the keys in an object MUST be unique. In the internal representation a JSON object is equivalent to a dictionary (see [WEBIDL]).
JSON-LD internal representation
The JSON-LD internal representation is the result of transforming a JSON syntactic structure into the core data structures suitable for direct processing: arrays, dictionaries, strings, numbers, booleans, and null.
null
The use of the null value within JSON-LD is used to ignore or reset values. A key-value pair in the @context where the value, or the @id of the value, is null explicitly decouples a term's association with an IRI. A key-value pair in the body of a JSON-LD document whose value is null has the same meaning as if the key-value pair was not defined. If @value, @list, or @set is set to null in expanded form, then the entire JSON object is ignored.
number
In the JSON serialization, a number is similar to that used in most programming languages, except that the octal and hexadecimal formats are not used and that leading zeros are not allowed. In the internal representation, a number is equivalent to either a long or double, depending on if the number has a non-zero fractional part (see [WEBIDL]).
scalar
A scalar is either a JSON string, number, true, or false.
string
A string is a sequence of zero or more Unicode (UTF-8) characters, wrapped in double quotes, using backslash escapes (if necessary). A character is represented as a single character string.
true and false
Values that are used to express one of two possible boolean states.

Furthermore, the following terminology is used throughout this document:

absolute IRI
An absolute IRI is defined in [RFC3987] containing a scheme along with a path and optional query and fragment segments.
active context
A context that is used to resolve terms while the processing algorithm is running.
base IRI
The base IRI is an absolute IRI established in the context, or is based on the JSON-LD document location. The base IRI is used to turn relative IRIs into absolute IRIs.
blank node
A node in a graph that is neither an IRI, nor a JSON-LD value, nor a list. A blank node does not contain a de-referenceable identifier because it is either ephemeral in nature or does not contain information that needs to be linked to from outside of the linked data graph. A blank node is assigned an identifier starting with the prefix _:.
blank node identifier
A blank node identifier is a string that can be used as an identifier for a blank node within the scope of a JSON-LD document. Blank node identifiers begin with _:.
compact IRI
A compact IRI is has the form of prefix:suffix and is used as a way of expressing an IRI without needing to define separate term definitions for each IRI contained within a common vocabulary identified by prefix.
context
A a set of rules for interpreting a JSON-LD document as specified in The Context of the JSON-LD Syntax specification [JSON-LD11CG].
datatype IRI
A datatype IRI as specified by [RDF11-CONCEPTS].
default graph
The default graph is the only graph in a JSON-LD document which has no graph name. When executing an algorithm, the graph where data should be placed if a named graph is not specified.
default language
The default language is set in the context using the @language key whose value MUST be a string representing a [BCP47] language code or null.
edge
Every edge has a direction associated with it and is labeled with an IRI or a blank node identifier. Within the JSON-LD syntax these edge labels are called properties. Whenever possible, an edge should be labeled with an IRI.
expanded term definition
An expanded term definition, is a term definition where the value is a JSON object containing one or more keyword properties to define the associated absolute IRI, if this is a reverse property, the type associated with string values, and a container mapping.
Frame
A JSON-LD document, which describes the form for transforming another JSON-LD document using matching and embedding rules. A frame document allows additional keywords and certain property values to describe the matching and transforming process.
graph name
The IRI identifying a named graph.
graph object
A graph object represents a named graph represented as the value of a property within a node object. When expanded, a graph object MUST have an @graph member, and may also have @id, and @index members. A simple graph object is a graph object which does not have an @id member. Note that node objects may have a @graph member, but are not considered graph objects if they include any other properties. A top-level object consisting of @graph is also not a graph object.
id map
An id map is a JSON object value of a term defined with @container set to @id, who's keys are interpreted as IRIs representing the @id of the associated node object; value MUST be a node object. If the value contains a property expanding to @id, it's value MUST be equivalent to the referencing key.
index map
An index map is a JSON object value of a term defined with @container set to @index, whose values MUST be any of the following types: string, number, true, false, null, node object, value object, list object, set object, or an array of zero or more of the above possibilities.
IRI
An Internationalized Resource Identifier as described in [RFC3987].
JSON-LD document
A JSON-LD document is a serialization of a collection of graphs and comprises exactly one default graph and zero or more named graphs.
JSON-LD Processor
A JSON-LD Processor is a system which can perform the algorithms defined in [JSON-LD11CG-API].
JSON-LD value
A JSON-LD value is a string, a number, true or false, a typed value, or a language-tagged string.
keyword
A JSON key that is specific to JSON-LD, specified in the JSON-LD Syntax specification [JSON-LD11CG] in the section titled Syntax Tokens and Keywords.
language map
An language map is a JSON object value of a term defined with @container set to @language, whose keys MUST be strings representing [BCP47] language codes and the values MUST be any of the following types: null, string, or an array of zero or more of the above possibilities.
language-tagged string
A language-tagged string consists of a string and a non-empty language tag as defined by [BCP47]. The language tag MUST be well-formed according to section 2.2.9 Classes of Conformance of [BCP47], and is normalized to lowercase.
linked data graph
A labeled directed graph, i.e., a set of nodes connected by edges, as specified in the Data Model section of the JSON-LD specification [JSON-LD11CG]. A linked data graph is a generalized representation of an RDF graph as defined in [RDF-CONCEPTS].
list
A list is an ordered sequence of IRIs, blank nodes, and JSON-LD values. See RDF collection in [RDF-SCHEMA].
list object
A list object is a JSON object that has an @list member.
local context
A context that is specified within a JSON object, specified via the @context keyword.
named graph
A named graph is a linked data graph that is identified by an IRI or blank node.
node
Every node is an IRI, a blank node, a JSON-LD value, or a list. A piece of information that is represented in a linked data graph.
node object
A node object represents zero or more properties of a node in the graph serialized by the JSON-LD document. A JSON object is a node object if it exists outside of the JSON-LD context and:
  • it does not contain the @value, @list, or @set keywords, or
  • it is not the top-most JSON object in the JSON-LD document consisting of no other members than @graph and @context.
object
An object is a node in a linked data graph with at least one incoming edge. See RDF objectin [RDF11-CONCEPTS].
prefix
A prefix is the first component of a compact IRI which comes from a term that maps to a string that, when prepended to the suffix of the compact IRI results in an absolute IRI.
processing mode
The processing mode defines how a JSON-LD document is processed. By default, all documents are assumed to be conformant with JSON-LD 1.0 [JSON-LD]. By defining a different version using the @version member in a context, or via explicit API option, other processing modes can be accessed. This specification defines extensions for the json-ld-1.1 processing mode.
property
The IRI label of an edge in a linked data graph. See RDF predicate in [RDF11-CONCEPTS].
RDF dataset
A dataset as specified by [RDF11-CONCEPTS] representing a collection of RDF graphs.
RDF resource
A resource as specified by [RDF11-CONCEPTS].
RDF triple
A triple as specified by [RDF11-CONCEPTS].
relative IRI
A relative IRI is an IRI that is relative to some other absolute IRI, typically the base IRI of the document. Note that properties, values of @type, and values of terms defined to be vocabulary relative are resolved relative to the vocabulary mapping, not the base IRI.
set object
A set object is a JSON object that has an @set member.
subject
A subject is anode in a linked data graph with at least one outgoing edge, related to an object node through a property. See RDF subject in [RDF11-CONCEPTS].
term
A term is a short word defined in a context that MAY be expanded to an IRI
term definition
A term definition is an entry in a context, where the key defines a term which may be used within a JSON object as a property, type, or elsewhere that a string is interpreted as a vocabulary item. Its value is either a string (simple term definition), expanding to an absolute IRI, or an expanded term definition.
type map
An type map is a JSON object value of a term defined with @container set to @type, who's keys are interpreted as IRIs representing the @type of the associated node object; value MUST be a node object, or array of node objects. If the value contains a property expanding to @type, it's values are merged with the map value when expanding.
typed value
A typed value consists of a value, which is a string, and a type, which is an IRI.
value object
A value object is a JSON object that has an @value member.
vocabulary mapping
The vocabulary mapping is set in the context using the @vocab key whose value MUST be an absolute IRI null.

1.2.1 Algorithm Terms §

The Following terms are used within specific algorithms.

active graph
The name of the currently active graph that the processor should use when processing.
active property
The currently active property or keyword that the processor should use when processing. The active property is represented in the original lexical form, which is used for finding coercion mappings in the active context.
JSON-LD input
The JSON-LD data structure that is provided as input to the algorithm.
promise
A promise is an object that represents the eventual result of a single asynchronous operation. Promises are defined in [ECMASCRIPT-6.0].

1.3 Typographical conventions §

The following typographic conventions are used in this specification:

markup
Markup (elements, attributes, properties), machine processable values (string, characters, media types), property name, or a file name is in red-orange monospace font.
variable
A variable in pseudo-code or in an algorithm description is in italics.
definition
A definition of a term, to be used elsewhere in this or other specifications, is in bold and italics.
definition reference
A reference to a definition in this document is underlined and is also an active link to the definition itself.
markup definition reference
A references to a definition in this document, when the reference itself is also a markup, is underlined, red-orange monospace font, and is also an active link to the definition itself.
external definition reference
A reference to a definition in another document is underlined, in italics, and is also an active link to the definition itself.
markup external definition reference
A reference to a definition in another document, when the reference itself is also a markup, is underlined, in italics red-orange monospace font, and is also an active link to the definition itself.
hyperlink
A hyperlink is underlined and in blue.
[reference]
A document reference (normative or informative) is enclosed in square brackets and links to the references section.
Changes from Recommendation
Sections or phrases changed from the previous Recommendation are highlighted.
Note

Notes are in light green boxes with a green left border and with a "Note" header in green. Notes are normative or informative depending on the whether they are in a normative or informative section, respectively.

Example 1
Examples are in light khaki boxes, with khaki left border, and with a
numbered "Example" header in khaki. Examples are always informative.
The content of the example is in monospace font and may be syntax colored.

1.4 Example Conventions §

Note that in the examples used in this document, output is of necessity shown in serialized form as JSON. While the algorithms describe operations on the JSON-LD internal representation, when they as displayed as examples, the JSON serialization is used. In particular, the internal representation use of dictionaries are represented using JSON objects.

Example 2: Sample JSON-LD document
{
  "@context": {
    "name": "http://xmlns.com/foaf/0.1/name",
    "knows": "http://xmlns.com/foaf/0.1/knows"
  },
  "@id": "http://me.markus-lanthaler.com/",
  "name": "Markus Lanthaler",
  "knows": [
    {
      "name": "Dave Longley"
    }
  ]
}

In the internal representation, the example above would be of a dictionary containing @context, @id, name, and knows keys, with either dictionaries, strings, or arrays of dictionaries or strings values. In the JSON serialization, JSON objects are used for dictionaries, while arrays and strings are serialized using a convention common to many programming languages.

2. Features §

This section is non-normative.

The JSON-LD 1.1 Syntax specification [JSON-LD11CG] defines a syntax to express Linked Data in JSON. Because there is more than one way to express Linked Data using this syntax, it is often useful to be able to transform JSON-LD documents so that they may be more easily consumed by specific applications.

To allow these algorithms to be adapted for syntaxes other than JSON, the algorithms operate on the JSON-LD internal representation, which uses the generic concepts of arrays, dictionaries, strings, numbers, booleans, and null to describe the data represented by a JSON document. Algorithms act on this internal representation with API entry points responsible for transforming between the concrete and internal representations.

JSON-LD uses contexts to allow Linked Data to be expressed in a way that is specifically tailored to a particular person or application. By providing a context, JSON data can be expressed in a way that is a natural fit for a particular person or application whilst also indicating how the data should be understood at a global scale. In order for people or applications to share data that was created using a context that is different from their own, a JSON-LD processor must be able to transform a document from one context to another. Instead of requiring JSON-LD processors to write specific code for every imaginable context switching scenario, it is much easier to specify a single algorithm that can remove any context. Similarly, another algorithm can be specified to subsequently apply any context. These two algorithms represent the most basic transformations of JSON-LD documents. They are referred to as expansion and compaction, respectively.

JSON-LD 1.1 introduces new features that are compatible with JSON-LD 1.0 [JSON-LD], but if processed by a JSON-LD 1.0 processor may produce different results. In order to detect this JSON-LD 1.1 requires that the processing mode be explicitly set to json-ld-1.1, either through the processingMode API option, or using the @version member within a context.

There are four major types of transformation that are discussed in this document: expansion, compaction, flattening, and RDF serialization/deserialization.

2.1 Expansion §

This section is non-normative.

The algorithm that removes context is called expansion. Before performing any other transformations on a JSON-LD document, it is easiest to remove any context from it and to make data structures more regular.

To get an idea of how context and data structuring affects the same data, here is an example of JSON-LD that uses only terms and is fairly compact:

Example 3: JSON-LD documenet using only terms
{
  "@context": {
    "name": "http://xmlns.com/foaf/0.1/name",
    "homepage": {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"
    }
  },
  "@id": "http://me.markus-lanthaler.com/",
  "name": "Markus Lanthaler",
  "homepage": "http://www.markus-lanthaler.com/"
}

The next input example uses one IRI to express a property and an array to encapsulate another, but leaves the rest of the information untouched.

Example 4: Sample JSON-LD document using an IRI instead of a term to express a property
{
  "@context": {
    "website": "http://xmlns.com/foaf/0.1/homepage"
  },
  "@id": "http://me.markus-lanthaler.com/",
  "http://xmlns.com/foaf/0.1/name": "Markus Lanthaler",
  "website": { "@id": "http://www.markus-lanthaler.com/" }
}

Note that both inputs are valid JSON-LD and both represent the same information. The difference is in their context information and in the data structures used. A JSON-LD processor can remove context and ensure that the data is more regular by employing expansion.

Expansion has two important goals: removing any contextual information from the document, and ensuring all values are represented in a regular form. These goals are accomplished by expanding all properties to absolute IRIs and by expressing all values in arrays in expanded form. Expanded form is the most verbose and regular way of expressing of values in JSON-LD; all contextual information from the document is instead stored locally with each value. Running the Expansion algorithm (expand) operation) against the above examples results in the following output:

Example 5: Expanded JSON-LD document using an IRI
[
  {
    "@id": "http://me.markus-lanthaler.com/",
    "http://xmlns.com/foaf/0.1/name": [
      { "@value": "Markus Lanthaler" }
    ],
    "http://xmlns.com/foaf/0.1/homepage": [
      { "@id": "http://www.markus-lanthaler.com/" }
    ]
  }
]

The example above is the JSON-LD serialization of the output of the expansion algorithm, where the algorithm's use of dictionaries are replaced with JSON objects.

Note that in the output above all context definitions have been removed, all terms and compact IRIs have been expanded to absolute IRIs, and all JSON-LD values are expressed in arrays in expanded form. While the output is more verbose and difficult for a human to read, it establishes a baseline that makes JSON-LD processing easier because of its very regular structure.

2.2 Compaction §

This section is non-normative.

While expansion removes context from a given input, compaction's primary function is to perform the opposite operation: to express a given input according to a particular context. Compaction applies a context that specifically tailors the way information is expressed for a particular person or application. This simplifies applications that consume JSON or JSON-LD by expressing the data in application-specific terms, and it makes the data easier to read by humans.

Compaction uses a developer-supplied context to shorten IRIs to terms or compact IRIs and JSON-LD values expressed in expanded form to simple values such as strings or numbers.

For example, assume the following expanded JSON-LD input document:

Example 6: Expanded sample document
[
  {
    "@id": "http://me.markus-lanthaler.com/",
    "http://xmlns.com/foaf/0.1/name": [
      { "@value": "Markus Lanthaler" }
    ],
    "http://xmlns.com/foaf/0.1/homepage": [
      { "@id": "http://www.markus-lanthaler.com/" }
    ]
  }
]

Additionally, assume the following developer-supplied JSON-LD context:

Example 7: JSON-LD context
{
  "@context": {
    "name": "http://xmlns.com/foaf/0.1/name",
    "homepage": {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"
    }
  }
}

Running the Compaction Algorithm (compact) operation) given the context supplied above against the JSON-LD input document provided above would result in the following output:

Example 8: Compacted sample document
{
  "@context": {
    "name": "http://xmlns.com/foaf/0.1/name",
    "homepage": {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"
    }
  },
  "@id": "http://me.markus-lanthaler.com/",
  "name": "Markus Lanthaler",
  "homepage": "http://www.markus-lanthaler.com/"
}

The example above is the JSON-LD serialization of the output of the compaction algorithm, where the algorithm's use of dictionaries are replaced with JSON objects.

Note that all IRIs have been compacted to terms as specified in the context, which has been injected into the output. While compacted output is useful to humans, it is also used to generate structures that are easy to program against. Compaction enables developers to map any expanded document into an application-specific compacted document. While the context provided above mapped http://xmlns.com/foaf/0.1/name to name, it could also have been mapped to any other term provided by the developer.

2.3 Flattening §

This section is non-normative.

While expansion ensures that a document is in a uniform structure, flattening goes a step further to ensure that the shape of the data is deterministic. In expanded documents, the properties of a single node may be spread across a number of different dictionaries. By flattening a document, all properties of a node are collected in a single dictionary and all blank nodes are labeled with a blank node identifier. This may drastically simplify the code required to process JSON-LD data in certain applications.

For example, assume the following JSON-LD input document:

Example 9: JSON-LD document in compact form
{
  "@context": {
    "name": "http://xmlns.com/foaf/0.1/name",
    "knows": "http://xmlns.com/foaf/0.1/knows"
  },
  "@id": "http://me.markus-lanthaler.com/",
  "name": "Markus Lanthaler",
  "knows": [
    {
      "name": "Dave Longley"
    }
  ]
}

Running the Flattening Algorithm (flatten) operation) with a context set to null to prevent compaction returns the following document:

Example 10: Flattened sample document in expanded form
[
  {
    "@id": "_:t0",
    "http://xmlns.com/foaf/0.1/name": [
      { "@value": "Dave Longley" }
    ]
  },
  {
    "@id": "http://me.markus-lanthaler.com/",
    "http://xmlns.com/foaf/0.1/name": [
      { "@value": "Markus Lanthaler" }
    ],
    "http://xmlns.com/foaf/0.1/knows": [
      { "@id": "_:t0" }
    ]
  }
]

The example above is the JSON-LD serialization of the output of the flattening algorithm, where the algorithm's use of dictionaries are replaced with JSON objects.

Note how in the output above all properties of a node are collected in a single dictionary and how the blank node representing "Dave Longley" has been assigned the blank node identifier _:t0.

To make it easier for humans to read or for certain applications to process it, a flattened document can be compacted by passing a context. Using the same context as the input document, the flattened and compacted document looks as follows:

Example 11: Flattened and compacted sample document
{
  "@context": {
    "name": "http://xmlns.com/foaf/0.1/name",
    "knows": "http://xmlns.com/foaf/0.1/knows"
  },
  "@graph": [
    {
      "@id": "_:t0",
      "name": "Dave Longley"
    }, {
      "@id": "http://me.markus-lanthaler.com/",
      "name": "Markus Lanthaler",
      "knows": { "@id": "_:t0" }
    }
  ]
}

Please note that the result of flattening and compacting a document is always a dictionary, (represented as a JSON object when serialized), which contains an @graph member that represents the default graph.

2.4 RDF Serialization/Deserialization §

This section is non-normative.

JSON-LD can be used to serialize RDF data as described in [RDF11-CONCEPTS]. This ensures that data can be round-tripped to and from any RDF syntax without any loss in fidelity.

For example, assume the following RDF input serialized in Turtle [TURTLE]:

Example 12: Sample Turtle document
<http://me.markus-lanthaler.com/> <http://xmlns.com/foaf/0.1/name> "Markus Lanthaler" .
<http://me.markus-lanthaler.com/> <http://xmlns.com/foaf/0.1/homepage> <http://www.markus-lanthaler.com/> .

Using the Serialize RDF as JSON-LD algorithm a developer could transform this document into expanded JSON-LD:

Example 13: Sample Turtle document converted to JSON-LD
[
  {
    "@id": "http://me.markus-lanthaler.com/",
    "http://xmlns.com/foaf/0.1/name": [
      { "@value": "Markus Lanthaler" }
    ],
    "http://xmlns.com/foaf/0.1/homepage": [
      { "@id": "http://www.markus-lanthaler.com/" }
    ]
  }
]

The example above is the JSON-LD serialization of the output of the Serialize RDF as JSON-LD algorithm, where the algorithm's use of dictionaries are replaced with JSON objects.

Note that the output above could easily be compacted using the technique outlined in the previous section. It is also possible to deserialize the JSON-LD document back to RDF using the Deserialize JSON-LD to RDF algorithm.

3. Conformance §

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words MAY, MUST, and MUST NOT are to be interpreted as described in [RFC2119].

There are two classes of products that can claim conformance to this specification: JSON-LD Processors, and RDF Serializers/Deserializers.

A conforming JSON-LD Processor is a system which can perform the Expansion, Compaction, and Flattening operations in a manner consistent with the algorithms defined in this specification.

JSON-LD Processors MUST NOT attempt to correct malformed IRIs or language tags; however, they MAY issue validation warnings. IRIs are not modified other than conversion between relative and absolute IRIs.

A conforming RDF Serializer/Deserializer is a system that can deserialize JSON-LD to RDF and serialize RDF as JSON-LD as defined in this specification.

The algorithms in this specification are generally written with more concern for clarity than efficiency. Thus, JSON-LD Processors may implement the algorithms given in this specification in any way desired, so long as the end result is indistinguishable from the result that would be obtained by the specification's algorithms.

In algorithm steps that describe operations on keywords, those steps also apply to keyword aliases.

Note

Implementers can partially check their level of conformance to this specification by successfully passing the test cases of the JSON-LD test suite [JSON-LD-TESTS]. Note, however, that passing all the tests in the test suite does not imply complete conformance to this specification. It only implies that the implementation conforms to aspects tested by the test suite.

4. Context Processing Algorithms §

4.1 Context Processing Algorithm §

When processing a JSON-LD data structure, each processing rule is applied using information provided by the active context. This section describes how to produce an active context.

The active context contains the active term definitions which specify how properties and values have to be interpreted as well as the current base IRI, the vocabulary mapping and the default language. Each term definition consists of an IRI mapping, a boolean flag reverse property, an optional type mapping or language mapping, an optional context, an optional nest value, an optional prefix flag, and an optional container mapping. A term definition can not only be used to map a term to an IRI, but also to map a term to a keyword, in which case it is referred to as a keyword alias.

When processing, active context is initialized without any term definitions, vocabulary mapping, or default language. If a local context is encountered during processing, a new active context is created by cloning the existing active context. Then the information from the local context is merged into the new active context. Given that local contexts may contain references to remote contexts, this includes their retrieval.

4.1.1 Overview §

This section is non-normative.

First we prepare a new active context result by cloning the current active context. Then we normalize the form of the original local context to an array. Local contexts may be in the form of a dictionary, a string, or an array containing a combination of the two. Finally we process each context contained in the local context array as follows.

Unless specified using processingMode API option, the processing mode is set using the @version member in a local context and affects the behavior of algorithms including expansion and compaction.

If context is a string, it represents a reference to a remote context. We dereference the remote context and replace context with the value of the @context key of the top-level object in the retrieved JSON-LD document. If there's no such key, an invalid remote context has been detected. Otherwise, we process context by recursively using this algorithm ensuring that there is no cyclical reference.

If context is a dictionary, we first update the base IRI, the vocabulary mapping, processing mode, and the default language by processing three specific keywords: @base, @vocab, @version, and @language. These are handled before any other keys in the local context because they affect how the other keys are processed. Please note that @base is ignored when processing remote contexts.

Then, for every other key in local context, we update the term definition in result. Since term definitions in a local context may themselves contain terms or compact IRIs, we may need to recurse. When doing so, we must ensure that there is no cyclical dependency, which is an error. After we have processed any term definition dependencies, we update the current term definition, which may be a keyword alias.

Finally, we return result as the new active context.

4.1.2 Algorithm §

This algorithm specifies how a new active context is updated with a local context. The algorithm takes three input variables: an active context, a local context, and an array remote contexts which is used to detect cyclical context inclusions. If remote contexts is not passed, it is initialized to an empty array.

  1. Initialize result to the result of cloning active context.
  2. If local context is not an array, set it to an array containing only local context.
  3. For each item context in local context:
    1. If context is null, set result to a newly-initialized active context and continue with the next context. In JSON-LD 1.0, the base IRI was given a default value here; this is now described conditionally in section 9. The Application Programming Interface.
    2. If context is a string,
      1. Set context to the result of resolving value against the base IRI which is established as specified in section 5.1 Establishing a Base URI of [RFC3986]. Only the basic algorithm in section 5.2 of [RFC3986] is used; neither Syntax-Based Normalization nor Scheme-Based Normalization are performed. Characters additionally allowed in IRI references are treated in the same way that unreserved characters are treated in URI references, per section 6.5 of [RFC3987].
      2. If context is in the remote contexts array, a recursive context inclusion error has been detected and processing is aborted; otherwise, add context to remote contexts.
      3. If context was previously dereferenced, then the processor MUST NOT do a further dereference, and context is set to the previously established internal representation.
      4. Otherwise, dereference context, transforming into the internal representation. If context cannot be dereferenced, or cannot be transformed into the internal representation, a loading remote context failed error has been detected and processing is aborted. If the dereferenced document has no top-level dictionary with an @context member, an invalid remote context has been detected and processing is aborted; otherwise, set context to the value of that member.
      5. Set result to the result of recursively calling this algorithm, passing result for active context, context for local context, and a copy of remote contexts.
      6. Continue with the next context.
    3. If context is not a dictionary, an invalid local context error has been detected and processing is aborted.
    4. If context has an @base key and remote contexts is empty, i.e., the currently being processed context is not a remote context:
      1. Initialize value to the value associated with the @base key.
      2. If value is null, remove the base IRI of result.
      3. Otherwise, if value is an absolute IRI, the base IRI of result is set to value.
      4. Otherwise, if value is a relative IRI and the base IRI of result is not null, set the base IRI of result to the result of resolving value against the current base IRI of result.
      5. Otherwise, an invalid base IRI error has been detected and processing is aborted.
    5. If context has an @version key:
      1. If the associated value is not 1.1, an invalid @version value has been detected, and processing is aborted.
      2. If processing mode is set to json-ld-1.0, a processing mode conflict error has been detected and processing is aborted.
      3. Set processing mode, to json-ld-1.1, if not already set.
    6. If context has an @vocab key:
      1. Initialize value to the value associated with the @vocab key.
      2. If value is null, remove any vocabulary mapping from result.
      3. Otherewise, if value the empty string (""), the effective value is the current base IRI.
      4. Otherwise, if value is an absolute IRI or blank node identifier, the vocabulary mapping of result is set to value. If it is not an absolute IRI, or a blank node identifier, an invalid vocab mapping error has been detected and processing is aborted.
    7. If context has an @language key:
      1. Initialize value to the value associated with the @language key.
      2. If value is null, remove any default language from result.
      3. Otherwise, if value is string, the default language of result is set to lowercased value. If it is not a string, an invalid default language error has been detected and processing is aborted.
    8. Create a dictionary defined to use to keep track of whether or not a term has already been defined or currently being defined during recursion.
    9. For each key-value pair in context where key is not @base, @vocab, or @language, invoke the Create Term Definition algorithm, passing result for active context, context for local context, key, and defined.
  4. Return result.

4.2 Create Term Definition §

This algorithm is called from the Context Processing algorithm to create a term definition in the active context for a term being processed in a local context.

4.2.1 Overview §

This section is non-normative.

term definitions are created by parsing the information in the given local context for the given term. If the given term is a compact IRI, it may omit an IRI mapping by depending on its prefix having its own term definition. If the prefix is a key in the local context, then its term definition must first be created, through recursion, before continuing. Because a term definition can depend on other term definitions, a mechanism must be used to detect cyclical dependencies. The solution employed here uses a map, defined, that keeps track of whether or not a term has been defined or is currently in the process of being defined. This map is checked before any recursion is attempted.

After all dependencies for a term have been defined, the rest of the information in the local context for the given term is taken into account, creating the appropriate IRI mapping, container mapping, and type mapping or language mapping for the term.

4.2.2 Algorithm §

The algorithm has four required inputs which are: an active context, a local context, a term, and a map defined.

  1. If defined contains the key term and the associated value is true (indicating that the term definition has already been created), return. Otherwise, if the value is false, a cyclic IRI mapping error has been detected and processing is aborted.
  2. Set the value associated with defined's term key to false. This indicates that the term definition is now being created but is not yet complete.
  3. Since keywords cannot be overridden, term must not be a keyword. Otherwise, a keyword redefinition error has been detected and processing is aborted.
  4. Remove any existing term definition for term in active context.
  5. Initialize value to a copy of the value associated with the key term in local context.
  6. If value is null or value is a dictionary containing the key-value pair @id-null, set the term definition in active context to null, set the value associated with defined's key term to true, and return.
  7. Otherwise, if value is a string, convert it to a dictionary consisting of a single member whose key is @id and whose value is value. Set simple term to true.
  8. Otherwise, value must be a dictionary, if not, an invalid term definition error has been detected and processing is aborted. Set simple term to false.
  9. Create a new term definition, definition.
  10. If value contains the key @type:
    1. Initialize type to the value associated with the @type key, which must be a string. Otherwise, an invalid type mapping error has been detected and processing is aborted.
    2. Set type to the result of using the IRI Expansion algorithm, passing active context, type for value, true for vocab, local context, and defined. If the expanded type is neither @id, nor @vocab, nor an absolute IRI, an invalid type mapping error has been detected and processing is aborted.
    3. Set the type mapping for definition to type.
  11. If value contains the key @reverse:
    1. If value contains @id or @nest, members, an invalid reverse property error has been detected and processing is aborted.
    2. If the value associated with the @reverse key is not a string, an invalid IRI mapping error has been detected and processing is aborted.
    3. Otherwise, set the IRI mapping of definition to the result of using the IRI Expansion algorithm, passing active context, the value associated with the @reverse key for value, true for vocab, local context, and defined. If the result is neither an absolute IRI nor a blank node identifier, i.e., it contains no colon (:), an invalid IRI mapping error has been detected and processing is aborted.
    4. If value contains an @container member, set the container mapping of definition to its value; if its value is neither @set, nor @index, nor null, an invalid reverse property error has been detected (reverse properties only support set- and index-containers) and processing is aborted.
    5. Set the reverse property flag of definition to true.
    6. Set the term definition of term in active context to definition and the value associated with defined's key term to true and return.
  12. Set the reverse property flag of definition to false.
  13. If value contains the key @id and its value does not equal term:
    1. If the value associated with the @id key is not a string, an invalid IRI mapping error has been detected and processing is aborted.
    2. Otherwise, set the IRI mapping of definition to the result of using the IRI Expansion algorithm, passing active context, the value associated with the @id key for value, true for vocab, local context, and defined. If the resulting IRI mapping is neither a keyword, nor an absolute IRI, nor a blank node identifier, an invalid IRI mapping error has been detected and processing is aborted; if it equals @context, an invalid keyword alias error has been detected and processing is aborted.
    3. If term does not contain a colon (:), simple term is true, and the, IRI mapping of definition ends with a URI gen-delim character, set the prefix flag in definition to true.
  14. Otherwise if the term contains a colon (:):
    1. If term is a compact IRI with a prefix that is a key in local context a dependency has been found. Use this algorithm recursively passing active context, local context, the prefix as term, and defined.
    2. If term's prefix has a term definition in active context, set the IRI mapping of definition to the result of concatenating the value associated with the prefix's IRI mapping and the term's suffix.
    3. Otherwise, term is an absolute IRI or blank node identifier. Set the IRI mapping of definition to term.
  15. Otherwise, if active context has a vocabulary mapping, the IRI mapping of definition is set to the result of concatenating the value associated with the vocabulary mapping and term. If it does not have a vocabulary mapping, an invalid IRI mapping error been detected and processing is aborted.
  16. If value contains the key @container:
    1. Initialize container to the value associated with the @container key, which must be either @graph, @id, @index, @language, @list, @set, or @type. or an array containing exactly any one of those keywords, an array containing @graph and either @id or @index optionally including @set, or an array containing a combination of @set and any of @index, @id, @type, @language in any order . Otherwise, an invalid container mapping has been detected and processing is aborted.
    2. If processingMode is json-ld-1.0 and the container value is @graph, @id, or @type, or is otherwise not a string, an invalid container mapping has been detected and processing is aborted.
    3. Set the container mapping of definition to container.
  17. If value contains the key @context:
    1. If processingMode is json-ld-1.0, an invalid term definition has been detected and processing is aborted.
    2. Initialize context to the value associated with the @context key, which is treated as a local context.
    3. Invoke the Context Processing algorithm using the active context and context as local context. If any error is detected, an invalid scoped context error has been detected and processing is aborted.
    4. Set the local context of definition to context.
  18. If value contains the key @language and does not contain the key @type:
    1. Initialize language to the value associated with the @language key, which must be either null or a string. Otherwise, an invalid language mapping error has been detected and processing is aborted.
    2. If language is a string set it to lowercased language. Set the language mapping of definition to language.
  19. If value contains the key @nest:
    1. If processingMode is json-ld-1.0, an invalid term definition has been detected and processing is aborted.
    2. Initialize nest value in defined to the value associated with the @nest key, which must be a string and must not be a keyword other than @nest. Otherwise, an invalid @nest value error has been detected and processing is aborted.
  20. If value contains the key @prefix:
    1. If processingMode is json-ld-1.0, or if term contains a colon (:), an invalid term definition has been detected and processing is aborted.
    2. Initialize the prefix flag to the value associated with the @prefix key, which must be a boolean. Otherwise, an invalid @prefix value error has been detected and processing is aborted.
  21. If the value contains any key other than @id, @reverse, @container, @context, @nest, @prefix, or @type, an invalid term definition error has been detected and processing is aborted.
  22. Set the term definition of term in active context to definition and set the value associated with defined's key term to true.

4.3 IRI Expansion §

In JSON-LD documents, some keys and values may represent IRIs. This section defines an algorithm for transforming a string that represents an IRI into an absolute IRI or blank node identifier. It also covers transforming keyword aliases into keywords.

IRI expansion may occur during context processing or during any of the other JSON-LD algorithms. If IRI expansion occurs during context processing, then the local context and its related defined map from the Context Processing algorithm are passed to this algorithm. This allows for term definition dependencies to be processed via the Create Term Definition algorithm.

4.3.1 Overview §

This section is non-normative.

In order to expand value to an absolute IRI, we must first determine if it is null, a term, a keyword alias, or some form of IRI. Based on what we find, we handle the specific kind of expansion; for example, we expand a keyword alias to a keyword and a term to an absolute IRI according to its IRI mapping in the active context. While inspecting value we may also find that we need to create term definition dependencies because we're running this algorithm during context processing. We can tell whether or not we're running during context processing by checking local context against null. We know we need to create a term definition in the active context when value is a key in the local context and the defined map does not have a key for value with an associated value of true. The defined map is used during Context Processing to keep track of which terms have already been defined or are in the process of being defined. We create a term definition by using the Create Term Definition algorithm.

4.3.2 Algorithm §

The algorithm takes two required and four optional input variables. The required inputs are an active context and a value to be expanded. The optional inputs are two flags, document relative and vocab, that specifying whether value can be interpreted as a relative IRI against the document's base IRI or the active context's vocabulary mapping, respectively, and a local context and a map defined to be used when this algorithm is used during Context Processing. If not passed, the two flags are set to false and local context and defined are initialized to null.

  1. If value is a keyword or null, return value as is.
  2. If local context is not null, it contains a key that equals value, and the value associated with the key that equals value in defined is not true, invoke the Create Term Definition algorithm, passing active context, local context, value as term, and defined. This will ensure that a term definition is created for value in active context during Context Processing.
  3. If active context has a term definition for value, and the associated IRI mapping is a keyword, return that keyword.
  4. If vocab is true and the active context has a term definition for value, return the associated IRI mapping.
  5. If value contains a colon (:), it is either an absolute IRI, a compact IRI, or a blank node identifier:
    1. Split value into a prefix and suffix at the first occurrence of a colon (:).
    2. If prefix is underscore (_) or suffix begins with double-forward-slash (//), return value as it is already an absolute IRI or a blank node identifier.
    3. If local context is not null, it contains a key that equals prefix, and the value associated with the key that equals prefix in defined is not true, invoke the Create Term Definition algorithm, passing active context, local context, prefix as term, and defined. This will ensure that a term definition is created for prefix in active context during Context Processing.
    4. If active context contains a term definition for prefix, return the result of concatenating the IRI mapping associated with prefix and suffix.
    5. Return value as it is already an absolute IRI.
  6. If vocab is true, and active context has a vocabulary mapping, return the result of concatenating the vocabulary mapping with value.
  7. Otherwise, if document relative is true set value to the result of resolving value against the base IRI. Only the basic algorithm in section 5.2 of [RFC3986] is used; neither Syntax-Based Normalization nor Scheme-Based Normalization are performed. Characters additionally allowed in IRI references are treated in the same way that unreserved characters are treated in URI references, per section 6.5 of [RFC3987].
  8. Return value as is.

5. Expansion Algorithms §

5.1 Expansion Algorithm §

This algorithm expands a JSON-LD document, such that all context definitions are removed, all terms and compact IRIs are expanded to absolute IRIs, blank node identifiers, or keywords and all JSON-LD values are expressed in arrays in expanded form.

5.1.1 Overview §

This section is non-normative.

Starting with its root element, we can process the JSON-LD document recursively, until we have a fully expanded result. When expanding an element, we can treat each one differently according to its type, in order to break down the problem:

  1. If the element is null, there is nothing to expand.
  2. Otherwise, if element is a scalar, we expand it according to the Value Expansion algorithm.
  3. Otherwise, if the element is an array, then we expand each of its items recursively and return them in a new array.
  4. Otherwise, element is a dictionary. We expand each of its keys, adding them to our result, and then we expand each value for each key recursively. Some of the keys will be terms or compact IRIs and others will be keywords or simply ignored because they do not have definitions in the context. Any IRIs will be expanded using the IRI Expansion algorithm.

Finally, after ensuring result is in an array, we return result.

5.1.2 Algorithm §

The algorithm takes three required and one optional input variables. The required inputs are an active context, an active property, and an element to be expanded. The optional input is the flag frame expansion the allows special forms of input used for frame expansion. To begin, the active property is set to null, and element is set to the JSON-LD input. If not passed, the frame expansion flag is set to false.

The algorithm also performs processing steps specific to expanding a JSON-LD Frame. For a frame, the @id and @type properties can accept an array of IRIs or an empty dictionary. The properties of a value object can also accept an array of strings, or an empty dictionary. Framing also uses additional keyword properties: (@explicit, @default, @embed, @explicit, @omitDefault, or @requireAll) which are preserved through expansion. Special processing for a JSON-LD Frame is invoked when the frame expansion flag is set to true.

  1. If element is null, return null.
  2. If active property is @default, set the frame expansion flag to false.
  3. If element is a scalar,
    1. If active property is null or @graph, drop the free-floating scalar by returning null.
    2. Return the result of the Value Expansion algorithm, passing the active context, active property, and element as value.
  4. If element is an array,
    1. Initialize an empty array, result.
    2. For each item in element:
      1. Initialize expanded item to the result of using this algorithm recursively, passing active context, active property, item as element, and the frame expansion flag.
      2. If the active property is @list or its container mapping includes @list, the expanded item must not be an array or a list object, otherwise a list of lists error has been detected and processing is aborted.
      3. If expanded item is an array, append each of its items to result. Otherwise, if expanded item is not null, append it to result.
    3. Return result.
  5. Otherwise element is a dictionary.
  6. If element contains the key @context, set active context to the result of the Context Processing algorithm, passing active context and the value of the @context key as local context.
  7. For each key/value pair in element where key expands to @type using the IRI Expansion algorithm, passing active context, key for value, and true for vocab:
    1. For each term which is a value of value ordered lexicographically, if term's term definition in active context has a local context, set active context to the result to the result of the Context Processing algorithm, passing active context and the value of the term's local context as local context.
  8. Initialize an empty dictionary, result.
  9. For each key and value in element, ordered lexicographically by key:
    1. If key is @context, continue to the next key.
    2. Set expanded property to the result of using the IRI Expansion algorithm, passing active context, key for value, and true for vocab.
    3. If expanded property is null or it neither contains a colon (:) nor it is a keyword, drop key by continuing to the next key.
    4. If expanded property is a keyword:
      1. If active property equals @reverse, an invalid reverse property map error has been detected and processing is aborted.
      2. If result has already an expanded property member, a colliding keywords error has been detected and processing is aborted.
      3. If expanded property is @id and value is not a string, an invalid @id value error has been detected and processing is aborted. Otherwise, set expanded value to the result of using the IRI Expansion algorithm, passing active context, value, and true for document relative. When the frame expansion flag is set, value may be an empty dictionary, or an array of one or more strings. expanded value will be an array of one or more of these, with string values expanded using the IRI Expansion Algorithm.
      4. If expanded property is @type and value is neither a string nor an array of strings, an invalid type value error has been detected and processing is aborted. Otherwise, set expanded value to the result of using the IRI Expansion algorithm, passing active context, true for vocab, and true for document relative to expand the value or each of its items. When the frame expansion flag is set, value may also be an empty dictionary.
      5. If expanded property is @graph, set expanded value to the result of using this algorithm recursively passing active context, @graph for active property, value for element, and the frame expansion flag, ensuring that expanded value is an array of one or more dictionaries.
      6. If expanded property is @value and value is not a scalar or null, an invalid value object value error has been detected and processing is aborted. Otherwise, set expanded value to value. If expanded value is null, set the @value member of result to null and continue with the next key from element. Null values need to be preserved in this case as the meaning of an @type member depends on the existence of an @value member. When the frame expansion flag is set, value may also be an empty dictionary or an array of scalar values. expanded value will be null, or an array of one or more scalar values.
      7. If expanded property is @language and value is not a string, an invalid language-tagged string error has been detected and processing is aborted. Otherwise, set expanded value to lowercased value. When the frame expansion flag is set, value may also be an empty dictionary or an array of zero or strings. expanded value will be an array of one or more string values converted to lower case.
      8. If expanded property is @index and value is not a string, an invalid @index value error has been detected and processing is aborted. Otherwise, set expanded value to value.
      9. If expanded property is @list:
        1. If active property is null or @graph, continue with the next key from element to remove the free-floating list.
        2. Otherwise, initialize expanded value to the result of using this algorithm recursively passing active context, active property, value for element, and the frame expansion flag.
        3. If expanded value is a list object, a list of lists error has been detected and processing is aborted.
      10. If expanded property is @set, set expanded value to the result of using this algorithm recursively, passing active context, active property, value for element, and the frame expansion flag.
      11. If expanded property is @reverse and value is not a dictionary, an invalid @reverse value error has been detected and processing is aborted. Otherwise
        1. Initialize expanded value to the result of using this algorithm recursively, passing active context, @reverse as active property, value as element, and the frame expansion flag.
        2. If expanded value contains an @reverse member, i.e., properties that are reversed twice, execute for each of its property and item the following steps:
          1. If result does not have a property member, create one and set its value to an empty array.
          2. Append item to the value of the property member of result.
        3. If expanded value contains members other than @reverse:
          1. If result does not have an @reverse member, create one and set its value to an empty dictionary.
          2. Reference the value of the @reverse member in result using the variable reverse map.
          3. For each property and items in expanded value other than @reverse:
            1. For each item in items:
              1. If item is a value object or list object, an invalid reverse property value has been detected and processing is aborted.
              2. If reverse map has no property member, create one and initialize its value to an empty array.
              3. Append item to the value of the property member in reverse map.
        4. Continue with the next key from element.
      12. If expanded property is @nest, add key to nests, initializing it to an empty array, if necessary. Continue with the next key from element.
      13. When the frame expansion flag is set, if expanded property is any other framing keyword (@explicit, @default, @embed, @explicit, @omitDefault, or @requireAll), set expanded value to the result of performing the Expansion Algorithm recursively, passing active context, active property, value for element, and the frame expansion flag.
      14. Unless expanded value is null, set the expanded property member of result to expanded value.
      15. Continue with the next key from element.
    5. If key's term definition in active context has a local context, set term context to the result of the Context Processing algorithm, passing active context and the value of the key's local context as local context. Otherwise, set term context to active context.
    6. Set container mapping to key's container mapping in term context.
    7. If container mapping includes @language and value is a dictionary then value is expanded from a language map as follows:
      1. Initialize expanded value to an empty array.
      2. For each key-value pair language-language value in value, ordered lexicographically by language:
        1. If language value is not an array set it to an array containing only language value.
        2. For each item in language value:
          1. item must be a string or null, otherwise an invalid language map value error has been detected and processing is aborted.
          2. Append a dictionary to expanded value that consists of two key-value pairs: (@value-item) and (@language-lowercased language), unless item is null. If language is @none, or expands to @none, do not set the @language member.
    8. Otherwise, if container mapping includes @index, @type, or @id and value is a dictionary then value is expanded from an map as follows:
      1. Initialize expanded value to an empty array.
      2. For each key-value pair index-index value in value, ordered lexicographically by index:
        1. If container mapping includes @type, and index's term definition in term context has a local context, set map context to the result of the Context Processing algorithm, passing term context as active context and the value of the index's local context as local context. Otherwise, set map context to term context.
        2. Set expanded index to the result of using the IRI Expansion algorithm, passing active context, index, and true for vocab.
        3. If index value is not an array set it to an array containing only index value.
        4. Initialize index value to the result of using this algorithm recursively, passing map context as active context, key as active property, index value as element, and the frame expansion flag.
        5. For each item in index value:
          1. If container mapping includes @graph and if item is not a graph object, set item to a new dictionary containing the key-value pair @graph-item, ensuring that the value is represented using an array.
          2. If container mapping includes @index and item does not have the key @index and expanded index is not @none, add the key-value pair (@index-index) to item.
          3. Otherwise, if container mapping includes @id and item does not have the key @id, add the key-value pair (@id-expanded index) to item, where expanded index is set to the result of using the IRI Expansion algorithm, passing active context, index, and true for document relative, unless expanded index is already set to @none.
          4. Otherwise, if container mapping includes @type set types to the concatenation of expanded index with any existing values of @type in item. If expanded index is @none, do not concatenate expanded index to types. Add the key-value pair (@type-types) to item.
          5. Append item to expanded value.
    9. Otherwise, initialize expanded value to the result of using this algorithm recursively, passing term context as active context, key for active property, value for element, and the frame expansion flag.
    10. If expanded value is null, ignore key by continuing to the next key from element.
    11. If container mapping includes @list and expanded value is not already a list object, convert expanded value to a list object by first setting it to an array containing only expanded value if it is not already an array, and then by setting it to a dictionary containing the key-value pair @list-expanded value.
    12. If container mapping includes @graph, convert expanded value into an array, if necessary, then convert each value ev in expanded value into a graph object:
      1. If ev is not a graph object, convert it into one by creating a dictionary containing the key-value pair @graph-ev where ev is represented as an array.
    13. Otherwise, if the term definition associated to key indicates that it is a reverse property
      1. If result has no @reverse member, create one and initialize its value to an empty dictionary.
      2. Reference the value of the @reverse member in result using the variable reverse map.
      3. If expanded value is not an array, set it to an array containing expanded value.
      4. For each item in expanded value
        1. If item is a value object or list object, an invalid reverse property value has been detected and processing is aborted.
        2. If reverse map has no expanded property member, create one and initialize its value to an empty array.
        3. Append item to the value of the expanded property member of reverse map.
    14. Otherwise, if key is not a reverse property:
      1. If result does not have an expanded property member, create one and initialize its value to an empty array.
      2. Append expanded value to value of the expanded property member of result.
    15. For each key nesting-key in nests
      1. Set nested values to the value of nesting-key in element, ensuring that it is an array.
      2. For each nested value in nested values:
        1. If nested value is not a dictionary, or any key within nested value expands to @value, an invalid @nest value error has been detected and processing is aborted.
        2. Recursively repeat step 7 using nested value for element.
  10. If result contains the key @value:
    1. The result must not contain any keys other than @value, @language, @type, and @index. It must not contain both the @language key and the @type key. Otherwise, an invalid value object error has been detected and processing is aborted.
    2. If the value of result's @value key is null, then set result to null.
    3. Otherwise, if the value of result's @value member is not a string and result contains the key @language, an invalid language-tagged value error has been detected (only strings can be language-tagged) and processing is aborted.
    4. Otherwise, if the result has an @type member and its value is not an IRI, an invalid typed value error has been detected and processing is aborted.
  11. Otherwise, if result contains the key @type and its associated value is not an array, set it to an array containing only the associated value.
  12. Otherwise, if result contains the key @set or @list:
    1. The result must contain at most one other key and that key must be @index. Otherwise, an invalid set or list object error has been detected and processing is aborted.
    2. If result contains the key @set, then set result to the key's associated value.
  13. If result contains only the key @language, set result to null.
  14. If active property is null or @graph, drop free-floating values as follows:
    1. If result is an empty dictionary or contains the keys @value or @list, set result to null.
    2. Otherwise, if result is a dictionary whose only key is @id, set result to null. When the frame expansion flag is set, a dictionary containing only the @id key is retained.
  15. Return result.

If, after the above algorithm is run, the result is a dictionary that contains only an @graph key, set the result to the value of @graph's value. Otherwise, if the result is null, set it to an empty array. Finally, if the result is not an array, then set the result to an array containing only the result.

5.2 Value Expansion §

Some values in JSON-LD can be expressed in a compact form. These values are required to be expanded at times when processing JSON-LD documents. A value is said to be in expanded form after the application of this algorithm.

5.2.1 Overview §

This section is non-normative.

If active property has a type mapping in the active context set to @id or @vocab, and the value is a string, a dictionary with a single member @id whose value is the result of using the IRI Expansion algorithm on value is returned.

Otherwise, the result will be a dictionary containing an @value member whose value is the passed value. Additionally, an @type member will be included if there is a type mapping associated with the active property or an @language member if value is a string and there is language mapping associated with the active property.

Note that values interpreted as IRIs fall into two categories: those that are document relative, and those that are vocabulary relative. Properties and values of @type, along with terms marked as "@type": "@vocab" are vocabulary relative, meaning that they need to be either a defined term, a compact IRI where the prefix is a term, or a string which is turned into an absolute IRI using the vocabulary mapping.

5.2.2 Algorithm §

The algorithm takes three required inputs: an active context, an active property, and a value to expand.

  1. If the active property has a type mapping in active context that is @id, and the value is a string, return a new dictionary containing a single key-value pair where the key is @id and the value is the result of using the IRI Expansion algorithm, passing active context, value, and true for document relative.
  2. If active property has a type mapping in active context that is @vocab, and the value is a string, return a new dictionary containing a single key-value pair where the key is @id and the value is the result of using the IRI Expansion algorithm, passing active context, value, true for vocab, and true for document relative.
  3. Otherwise, initialize result to a dictionary with an @value member whose value is set to value.
  4. If active property has a type mapping in active context, other than @id or @vocab, add an @type member to result and set its value to the value associated with the type mapping.
  5. Otherwise, if value is a string:
    1. If a language mapping is associated with active property in active context, add an @language to result and set its value to the language code associated with the language mapping; unless the language mapping is set to null in which case no member is added.
    2. Otherwise, if the active context has a default language, add an @language to result and set its value to the default language.
  6. Return result.

6. Compaction Algorithms §

6.1 Compaction Algorithm §

This algorithm compacts a JSON-LD document, such that the given context is applied. This must result in shortening any applicable IRIs to terms or compact IRIs, any applicable keywords to keyword aliases, and any applicable JSON-LD values expressed in expanded form to simple values such as strings or numbers.

6.1.1 Overview §

This section is non-normative.

Starting with its root element, we can process the JSON-LD document recursively, until we have a fully compacted result. When compacting an element, we can treat each one differently according to its type, in order to break down the problem:

  1. If the element is a scalar, it is already in compacted form, so we simply return it.
  2. If the element is an array, we compact each of its items recursively and return them in a new array.
  3. Otherwise element is a dictionary. The value of each key in element is compacted recursively. Some of the keys will be compacted, using the IRI Compaction algorithm, to terms or compact IRIs and others will be compacted from keywords to keyword aliases or simply left unchanged because they do not have definitions in the context. Values will be converted to compacted form via the Value Compaction algorithm. Some data will be reshaped based on container mapping specified in the context such as @index or @language maps.

The final output is a dictionary with an @context key, if a non-empty context was given, where the dictionary is either result or a wrapper for it where result appears as the value of an (aliased) @graph key because result contained two or more items in an array.

6.1.2 Algorithm §

The algorithm takes five required input variables: an active context, an inverse context, an active property, an element to be compacted, and a flag compactArrays To begin, the active context is set to the result of performing Context Processing on the passed context, the inverse context is set to the result of performing the Inverse Context Creation algorithm on active context, the active property is set to null, element is set to the result of performing the Expansion algorithm on the JSON-LD input, and, if not passed, compactArrays is set to true.

  1. If the term definition for active property has a local context:
    1. Set active context to the result of the Context Processing algorithm, passing active context and the value of the active property's local context as local context.
    2. Set inverse context using the Inverse Context Creation algorithm using active context.
  2. If element is a scalar, it is already in its most compact form, so simply return element.
  3. If element is an array:
    1. Initialize result to an empty array.
    2. For each item in element:
      1. Initialize compacted item to the result of using this algorithm recursively, passing active context, inverse context, active property, and item for element.
      2. If compacted item is not null, then append it to result.
    3. If result contains only one item (it has a length of 1), active property is not @graph or @set, or the container mapping for active property in active context does not include @list or @set, and compactArrays is true, set result to its only item.
    4. Return result.
  4. Otherwise element is a dictionary. If element has an @value or @id member and the result of using the Value Compaction algorithm, passing active context, inverse context, active property,and element as value is a scalar, return that result.
  5. Initialize inside reverse to true if active property equals @reverse, otherwise to false.
  6. Initialize result to an empty dictionary.
  7. If element has a @type member, create a new array compacted types initialized by transforming each expanded type of that member into it's compacted form using the IRI Compaction algorithm, passing active context, inverse context, expanded type for var, and true for vocab. Then, for each term in compacted types ordered lexicographically:
    1. If the term definition for term has a local context:
      1. Set active context to the result of the Context Processing algorithm, passing active context and the value of term's local context as local context.
      2. Set inverse context using the Inverse Context Creation algorithm using active context.
  8. For each key expanded property and value expanded value in element, ordered lexicographically by expanded property:
    1. If expanded property is @id or @type:
      1. If expanded value is a string, then initialize compacted value to the result of using the IRI Compaction algorithm, passing active context, inverse context, expanded value for var, and true for vocab if expanded property is @type, false otherwise.
      2. Otherwise, expanded value must be a @type array:
        1. Initialize compacted value to an empty array.
        2. For each item expanded type in expanded value:
          1. Set term to the result of of using the IRI Compaction algorithm, passing active context, inverse context, expanded type for var, and true for vocab.
          2. Append term, to compacted value.
        3. If compacted value contains only one item (it has a length of 1), then set compacted value to its only item.
      3. Initialize alias to the result of using the IRI Compaction algorithm, passing active context, inverse context, expanded property for var, and true for vocab.
      4. Add a member alias to result whose value is set to compacted value and continue to the next expanded property.
    2. If expanded property is @reverse:
      1. Initialize compacted value to the result of using this algorithm recursively, passing active context, inverse context, @reverse for active property, and expanded value for element.
      2. For each property and value in compacted value:
        1. If the term definition for property in the active context indicates that property is a reverse property
          1. If the term definition for property in the active context has a container mapping including @set or compactArrays is false, and value is not an array, set value to a new array containing only value.
          2. If property is not a member of result, add one and set its value to value.
          3. Otherwise, if the value of the property member of result is not an array, set it to a new array containing only the value. Then append value to its value if value is not an array, otherwise append each of its items.
          4. Remove the property member from compacted value.
      3. If compacted value has some remaining members, i.e., it is not an empty dictionary:
        1. Initialize alias to the result of using the IRI Compaction algorithm, passing active context, inverse context, @reverse for var, and true for vocab.
        2. Set the value of the alias member of result to compacted value.
      4. Continue with the next expanded property from element.
    3. If expanded property is @preserve then:
      1. Initialize compacted value to the result of using this algorithm recursively, passing active context, inverse context, property for active property, and expanded value for element.
      2. Add expanded value as the value of @preserve in result unless expanded value is an empty array.
    4. If expanded property is @index and active property has a container mapping in active context that includes @index, then the compacted result will be inside of an @index container, drop the @index property by continuing to the next expanded property.
    5. Otherwise, if expanded property is @index, @value, or @language:
      1. Initialize alias to the result of using the IRI Compaction algorithm, passing active context, inverse context, expanded property for var, and true for vocab.
      2. Add a member alias to result whose value is set to expanded value and continue with the next expanded property.
    6. If expanded value is an empty array:
      1. Initialize item active property to the result of using the IRI Compaction algorithm, passing active context, inverse context, expanded property for var, expanded value for value, true for vocab, and inside reverse.
      2. If the term definition for item active property in the active context has a nest value, that value (nest term) must be @nest, or a term in the active context that expands to @nest, otherwise an invalid @nest value error has been detected, and processing is aborted. If result does not have the key that equals nest term, initialize it to an empty JSON object (nest object). If nest object does not have the key that equals item active property, set this key's value in nest object to an empty array.Otherwise, if the key's value is not an array, then set it to one containing only the value.
      3. Otherwise, if result does not have the key that equals item active property, set this key's value in result to an empty array. Otherwise, if the key's value is not an array, then set it to one containing only the value.
    7. At this point, expanded value must be an array due to the Expansion algorithm. For each item expanded item in expanded value:
      1. Initialize item active property to the result of using the IRI Compaction algorithm, passing active context, inverse context, expanded property for var, expanded item for value, true for vocab, and inside reverse.
      2. If the term definition for item active property in the active context has a nest value member, that value (nest term) must be @nest, or a term in the active context that expands to @nest, otherwise an invalid @nest value error has been detected, and processing is aborted. Set nest result to the value of nest term in result, initializing it to a new dictionary, if necessary; otherwise set nest result to result.
      3. Initialize container to null. If there is a container mapping for item active property in active context, set container to the first such value other than @set.
      4. Initialize as array to true or false depending on if the container mapping for item active property in active context includes @set or if item active property is @graph or @list.
      5. Initialize compacted item to the result of using this algorithm recursively, passing active context, inverse context, item active property for active property, expanded item for element if it does not contain the key @list and is not a graph object containing @list, otherwise pass the key's associated value for element.
      6. If expanded item is a list object:
        1. If compacted item is not an array, then set it to an array containing only compacted item.
        2. If container is not @list:
          1. Convert compacted item to a list object by setting it to a dictionary containing key-value pair where the key is the result of the IRI Compaction algorithm, passing active context, inverse context, @list for var, and compacted item for value and the value is the original compacted item.
          2. If expanded item contains the key @index, then add a key-value pair to compacted item where the key is the result of the IRI Compaction algorithm, passing active context, inverse context, @index as var, and the value associated with the @index key in expanded item as value.
        3. Otherwise, item active property must not be a key in nest result because there cannot be two list objects associated with an active property that has a container mapping; a compaction to list of lists error has been detected and processing is aborted.
      7. If expanded item is a graph object:
        1. If container includes @graph and @id:
          1. Initialize map object to the value of item active property in nest result.
          2. Initialize map key to the result of calling the IRI Compaction algorithm passing active context and the value of @id in expanded item or @none if no such value exists as var, with vocab set to true if there is no @id member in expanded item.
          3. If compacted item is not an array and as array is true, set compacted item to an array containing that value.
          4. If map key is not a key in map object, then set this key's value in map object to compacted item. Otherwise, if the value is not an array, then set it to one containing only the value and then append compacted item to it.
        2. Otherwise, if container includes @graph and @index and expanded item is a simple graph object:
          1. Initialize map object to the value of item active property in nest result.
          2. Initialize map key the value of @index in expanded item or @none, if no such value exists.
          3. If compacted item is not an array and as array is true, set compacted item to an array containing that value.
          4. If map key is not a key in map object, then set this key's value in map object to compacted item. Otherwise, if the value is not an array, then set it to one containing only the value and then append compacted item to it.
        3. Otherwise, if container includes @graph and expanded item is a simple graph object the value cannot be represented as a map object. If compacted item is not an array and as array is true, set compacted item to an array containing that value. If the value associated with the key that equals item active property in nest result is not an array, set it to a new array containing only the value. Then append compacted item to the value if compacted item is not an array, otherwise, concatenate it.
        4. Otherwise, container does not include @graph or otherwise does not match one of the previous cases, redo compacted item.
          1. Set compacted item to a new dictionary containing the key resulting from calling the IRI Compaction algorithm passing active context, @graph as var, and true for vocab using the original compacted item as a value.
          2. If expanded item contains the key @id, add the key resulting from calling the IRI Compaction algorithm passing active context, @id as var, and true for vocab using the value resulting from calling the IRI Compaction algorithm passing active context, the value of @id in expanded item as var.
          3. If expanded item contains the key @index, add the key resulting from calling the IRI Compaction algorithm passing active context, @index as var, and true for vocab using the value of @index in expanded item.
          4. If as array is true, set compacted item to an array containing that value.
          5. Then append compacted item to the value if compacted item is not an array, otherwise, concatenate it.
      8. Otherwise, if container includes @language, @index, @id, or @type and container does not include @graph:
        1. If item active property is not a key in nest result, initialize it to an empty dictionary. Initialize map object to the value of item active property in nest result.
        2. Set container key to the result of calling the IRI Compaction algorithm passing active context, either @language, @index, @id, or @type based on the contents of container, as var, and true for vocab.
        3. If container includes @language and expanded item contains the key @value, then set compacted item to the value associated with its @value key. Set map key to the value of @language in expanded item, if any.
        4. If container includes @index set map key to the value of @index in expanded item, if any, and remove container key from compacted item.
        5. If container includes @id, set map key to the value of container key in compacted item and remove container key from compacted item.
        6. If container is @type, set map key to the first value of container key in compacted item, if any. If there are remaining values in compacted item for compacted container, set the value of compacted container in compacted value to those remaining values. Otherwise, remove that key-value pair from compacted item.
        7. If compacted item is not an array and as array is true, set compacted item to an array containing that value.
        8. If map key is null, set it to the result of calling the IRI Compaction algorithm passing active context, @none as var, and true for vocab.
        9. If map key is not a key in map object, then set this key's value in map object to compacted item. Otherwise, if the value is not an array, then set it to one containing only the value and then append compacted item to it.
      9. Otherwise,
        1. If compactArrays is false, as array is true and compacted item is not an array, set it to a new array containing only compacted item.
        2. If item active property is not a key in result then add the key-value pair, (item active property-compacted item), to nest result.
        3. Otherwise, if the value associated with the key that equals item active property in nest result is not an array, set it to a new array containing only the value. Then append compacted item to the value if compacted item is not an array, otherwise, concatenate it.
  9. Return result.

If, after the algorithm outlined above is run, result is an empty array, replace it with a new dictionary. Otherwise, if result is an array, replace it with a new dictionary with a single member whose key is the result of using the IRI Compaction algorithm, passing active context, inverse context, and @graph as var and whose value is the array result.

Finally, if a non-empty context has been passed, add an @context member to result and set its value to the passed context.

6.2 Inverse Context Creation §

When there is more than one term that could be chosen to compact an IRI, it has to be ensured that the term selection is both deterministic and represents the most context-appropriate choice whilst taking into consideration algorithmic complexity.

In order to make term selections, the concept of an inverse context is introduced. An inverse context is essentially a reverse lookup table that maps container mapping, type mappings, and language mappings to a simple term for a given active context. A inverse context only needs to be generated for an active context if it is being used for compaction.

To make use of an inverse context, a list of preferred container mapping and the type mapping or language mapping are gathered for a particular value associated with an IRI. These parameters are then fed to the Term Selection algorithm, which will find the term that most appropriately matches the value's mappings.

6.2.1 Overview §

This section is non-normative.

To create an inverse context for a given active context, each term in the active context is visited, ordered by length, shortest first (ties are broken by choosing the lexicographically least term). For each term, an entry is added to the inverse context for each possible combination of container mapping and type mapping or language mapping that would legally match the term. Illegal matches include differences between a value's type mapping or language mapping and that of the term. If a term has no container mapping, type mapping, or language mapping (or some combination of these), then it will have an entry in the inverse context using the special key @none. This allows the Term Selection algorithm to fall back to choosing more generic terms when a more specifically-matching term is not available for a particular IRI and value combination.

6.2.2 Algorithm §

The algorithm takes one required input: the active context that the inverse context is being created for.

  1. Initialize result to an empty dictionary.
  2. Initialize default language to @none. If the active context has a default language, set default language to it.
  3. For each key term and value term definition in the active context, ordered by shortest term first (breaking ties by choosing the lexicographically least term):
    1. If the term definition is null, term cannot be selected during compaction, so continue to the next term.
    2. Initialize container to @none. If the container mapping is not empty, set container to the concatenation of all values of the container mapping in lexicographically order .
    3. Initialize var to the value of the IRI mapping for the term definition.
    4. If var is not a key in result, add a key-value pair where the key is var and the value is an empty dictionary to result.
    5. Reference the value associated with the var member in result using the variable container map.
    6. If container map has no container member, create one and set its value to a new dictionary with three members. The first member is @language and its value is a new empty dictionary, the second member is @type and its value is a new empty dictionary, and the third member is @any and its value is a new dictionary with the member @none set to the term being processed.
    7. Reference the value associated with the container member in container map using the variable type/language map.
    8. If the term definition indicates that the term represents a reverse property:
      1. Reference the value associated with the @type member in type/language map using the variable type map.
      2. If type map does not have an @reverse member, create one and set its value to the term being processed.
    9. Otherwise, if term definition has a type mapping:
      1. Reference the value associated with the @type member in type/language map using the variable type map.
      2. If type map does not have a member corresponding to the type mapping in term definition, create one and set its value to the term being processed.
    10. Otherwise, if term definition has a language mapping (might be null):
      1. Reference the value associated with the @language member in type/language map using the variable language map.
      2. If the language mapping equals null, set language to @null; otherwise set it to the language code in language mapping.
      3. If language map does not have a language member, create one and set its value to the term being processed.
    11. Otherwise:
      1. Reference the value associated with the @language member in type/language map using the variable language map.
      2. If language map does not have a default language member, create one and set its value to the term being processed.
      3. If language map does not have an @none member, create one and set its value to the term being processed.
      4. Reference the value associated with the @type member in type/language map using the variable type map.
      5. If type map does not have an @none member, create one and set its value to the term being processed.
  4. Return result.

6.3 IRI Compaction §

This algorithm compacts an IRI to a term or compact IRI, or a keyword to a keyword alias. A value that is associated with the IRI may be passed in order to assist in selecting the most context-appropriate term.

6.3.1 Overview §

This section is non-normative.

If the passed IRI is null, we simply return null. Otherwise, we first try to find a term that the IRI or keyword can be compacted to if it is relative to active context's vocabulary mapping. In order to select the most appropriate term, we may have to collect information about the passed value. This information includes which container mapping would be preferred for expressing the value, and what its type mapping or language mapping is. For JSON-LD lists, the type mapping or language mapping will be chosen based on the most specific values that work for all items in the list. Once this information is gathered, it is passed to the Term Selection algorithm, which will return the most appropriate term to use.

If no term was found that could be used to compact the IRI, an attempt is made to compact the IRI using the active context's vocabulary mapping, if there is one. If the IRI could not be compacted, an attempt is made to find a compact IRI. A term will be used to create a compact IRI only if the term definition contains the prefix flag with the value true. If there is no appropriate compact IRI, and the compactToRelative option is true, the IRI is transformed to a relative IRI using the document's base IRI. Finally, if the IRI or keyword still could not be compacted, it is returned as is.

6.3.2 Algorithm §

This algorithm takes three required inputs and three optional inputs. The required inputs are an active context, an inverse context, and the var to be compacted. The optional inputs are a value associated with the var, a vocab flag which specifies whether the passed var should be compacted using the active context's vocabulary mapping, and a reverse flag which specifies whether a reverse property is being compacted. If not passed, value is set to null and vocab and reverse are both set to false.

  1. If var is null, return null.
  2. If vocab is true and var is a key in inverse context:
    1. Initialize default language to active context's default language, if it has one, otherwise to @none.
    2. If value is a dictionary containing the property @preserve, use the first element from the value of @preserve as value.
    3. Initialize containers to an empty array. This array will be used to keep track of an ordered list of preferred container mapping for a term, based on what is compatible with value.
    4. Initialize type/language to @language, and type/language value to @null. These two variables will keep track of the preferred type mapping or language mapping for a term, based on what is compatible with value.
    5. If value is a dictionary, that contains the key @index, and value is not a graph object then append the values @index and @index@set to containers.
    6. If reverse is true, set type/language to @type, type/language value to @reverse, and append @set to containers.
    7. Otherwise, if value is a list object, then set type/language and type/language value to the most specific values that work for all items in the list as follows:
      1. If @index is a not key in value, then append @list to containers.
      2. Initialize list to the array associated with the key @list in value.
      3. Initialize common type and common language to null. If list is empty, set common language to default language.
      4. For each item in list:
        1. Initialize item language to @none and item type to @none.
        2. If item contains the key @value:
          1. If item contains the key @language, then set item language to its associated value.
          2. Otherwise, if item contains the key @type, set item type to its associated value.
          3. Otherwise, set item language to @null.
        3. Otherwise, set item type to @id.
        4. If common language is null, set it to item language.
        5. Otherwise, if item language does not equal common language and item contains the key @value, then set common language to @none because list items have conflicting languages.
        6. If common type is null, set it to item type.
        7. Otherwise, if item type does not equal common type, then set common type to @none because list items have conflicting types.
        8. If common language is @none and common type is @none, then stop processing items in the list because it has been detected that there is no common language or type amongst the items.
      5. If common language is null, set it to @none.
      6. If common type is null, set it to @none.
      7. If common type is not @none then set type/language to @type and type/language value to common type.
      8. Otherwise, set type/language value to common language.
    8. Otherwise, if value is a graph object, prefer a mapping most appropriate for the particular value.
      1. If value contains the key @index, append the values @graph@index and @graph@index@set to containers.
      2. If the value contains the key @id, append the values @graph@id and @graph@id@set to containers.
      3. Append the values @graph @graph@set, and @set to containers.
      4. If value does not contain the key @index, append the values @graph@index and @graph@index@set to containers.
      5. If the value does not contain the key @id, append the values @graph@id and @graph@id@set to containers.
      6. Append the values @index and @index@set to containers.
    9. Otherwise:
      1. If value is a value object:
        1. If value contains the key @language and does not contain the key @index, then set type/language value to its associated value and, append @language and @language@set to containers.
        2. Otherwise, if value contains the key @type, then set type/language value to its associated value and set type/language to @type.
      2. Otherwise, set type/language to @type and set type/language value to @id, and append @id, @id@set, @type, and @set@type, to containers.
      3. Append @set to containers.
    10. Append @none to containers. This represents the non-existence of a container mapping, and it will be the last container mapping value to be checked as it is the most generic.
    11. If processing mode is json-ld-1.1 and value does not contain the key @index, append @index and @index@set to containers.
    12. If processing mode is json-ld-1.1 and value contains only the key @value, append @language and @language@set to containers.
    13. If type/language value is null, set it to @null. This is the key under which null values are stored in the inverse context entry.
    14. Initialize preferred values to an empty array. This array will indicate, in order, the preferred values for a term's type mapping or language mapping.
    15. If type/language value is @reverse, append @reverse to preferred values.
    16. If type/language value is @id or @reverse and value has an @id member:
      1. If the result of using the IRI compaction algorithm, passing active context, inverse context, the value associated with the @id key in value for var, and true for vocab has a term definition in the active context with an IRI mapping that equals the value associated with the @id key in value, then append @vocab, @id, and @none, in that order, to preferred values.
      2. Otherwise, append @id, @vocab, and @none, in that order, to preferred values.
    17. Otherwise, append type/language value and @none, in that order, to preferred values. If value is an empty list object, set type/language to @any.
    18. Initialize term to the result of the Term Selection algorithm, passing inverse context, var, containers, type/language, and preferred values.
    19. If term is not null, return term.
  3. At this point, there is no simple term that var can be compacted to. If vocab is true and active context has a vocabulary mapping:
    1. If var begins with the vocabulary mapping's value but is longer, then initialize suffix to the substring of var that does not match. If suffix does not have a term definition in active context, then return suffix.
  4. The var could not be compacted using the active context's vocabulary mapping. Try to create a compact IRI, starting by initializing compact IRI to null. This variable will be used to tore the created compact IRI, if any.
  5. For each key term and value term definition in the active context:
    1. If the term definition is null, its IRI mapping equals var, its IRI mapping is not a substring at the beginning of var, or the term definition does not contain the prefix flag having a value of true, the term cannot be used as a prefix. Continue with the next term.
    2. Initialize candidate by concatenating term, a colon (:), and the substring of var that follows after the value of the term definition's IRI mapping.
    3. If either compact IRI is null, candidate is shorter or the same length but lexicographically less than compact IRI and candidate does not have a term definition in active context, or if the term definition has an IRI mapping that equals var and value is null, set compact IRI to candidate.
  6. If compact IRI is not null, return compact IRI.
  7. If vocab is false, transform var to a relative IRI using the base IRI from active context, if it exists.
  8. Finally, return var as is.

6.4 Term Selection §

This algorithm, invoked via the IRI Compaction algorithm, makes use of an active context's inverse context to find the term that is best used to compact an IRI. Other information about a value associated with the IRI is given, including which container mapping and which type mapping or language mapping would be best used to express the value.

6.4.1 Overview §

This section is non-normative.

The inverse context's entry for the IRI will be first searched according to the preferred container mapping, in the order that they are given. Amongst terms with a matching container mapping, preference will be given to those with a matching type mapping or language mapping, over those without a type mapping or language mapping. If there is no term with a matching container mapping then the term without a container mapping that matches the given type mapping or language mapping is selected. If there is still no selected term, then a term with no type mapping or language mapping will be selected if available. No term will be selected that has a conflicting type mapping or language mapping. Ties between terms that have the same mappings are resolved by first choosing the shortest terms, and then by choosing the lexicographically least term. Note that these ties are resolved automatically because they were previously resolved when the Inverse Context Creation algorithm was used to create the inverse context.

6.4.2 Algorithm §

This algorithm has five required inputs. They are: an inverse context, a keyword or IRI var, an array containers that represents an ordered list of preferred container mapping, a string type/language that indicates whether to look for a term with a matching type mapping or language mapping, and an array representing an ordered list of preferred values for the type mapping or language mapping to look for.

  1. Initialize container map to the value associated with var in the inverse context.
  2. For each item container in containers:
    1. If container is not a key in container map, then there is no term with a matching container mapping for it, so continue to the next container.
    2. Initialize type/language map to the value associated with the container member in container map.
    3. Initialize value map to the value associated with type/language member in type/language map.
    4. For each item in preferred values:
      1. If item is not a key in value map, then there is no term with a matching type mapping or language mapping, so continue to the next item.
      2. Otherwise, a matching term has been found, return the value associated with the item member in value map.
  3. No matching term has been found. Return null.

6.4.3 Examples §

This section is non-normative.

The following examples are intended to illustrate how the term selection algorithm behaves for different term definitions and values. It is not comprehensive, but intended to illustrate different parts of the algorithm.

6.4.3.1 Language Map Term §

If the term definition has "@container": "@language", it will only match a value object having no @type.

Example 14: Term definition with language map
{
  "@context": {"t": {"@id": "http://example/t", "@container": "@language"}}
}

The inverse context will contain the following:

{
  "@language": {
    "@language": {"@none": "t"},
    "@type": {"@none": "t"},
    "@any": {"@none": "t"}
  }
}
        
6.4.3.2 Datatyped Term §

If the term definition has a datatype, it will only match a value object having a matching datatype.

Example 16: Term definition with datatype
{
  "@context": {"t": {"@id": "http://example/t", "@type": "http:/example/type"}}
}

The inverse context will contain the following:

{
  "@none": {
    "@language": {},
    "@type": {"http:/example/type": "t"},
    "@any": {"@none": "t"}
  }
}
        

6.5 Value Compaction §

Expansion transforms all values into expanded form in JSON-LD. This algorithm performs the opposite operation, transforming a value into compacted form. This algorithm compacts a value according to the term definition in the given active context that is associated with the value's associated active property.

6.5.1 Overview §

This section is non-normative.

The value to compact has either an @id or an @value member.

For the former case, if the type mapping of active property is set to @id or @vocab and value consists of only an @id member and, if the container mapping of active property includes @index, an @index member, value can be compacted to a string by returning the result of using the IRI Compaction algorithm to compact the value associated with the @id member. Otherwise, value cannot be compacted and is returned as is.

For the latter case, it might be possible to compact value just into the value associated with the @value member. This can be done if the active property has a matching type mapping or language mapping and there is either no @index member or the container mapping of active property includes @index. It can also be done if @value is the only member in value (apart an @index member in case the container mapping of active property includes @index) and either its associated value is not a string, there is no default language, or there is an explicit null language mapping for the active property.

6.5.2 Algorithm §

This algorithm has four required inputs: an active context, an inverse context, an active property, and a value to be compacted.

  1. Initialize number members to the number of members value contains.
  2. If value has an @index member and the container mapping associated to active property includes @index, decrease number members by 1.
  3. If number members is greater than 2, return value as it cannot be compacted.
  4. If value has an @id member:
    1. If number members is 1 and the type mapping of active property is set to @id, return the result of using the IRI compaction algorithm, passing active context, inverse context, and the value of the @id member for var.
    2. Otherwise, if number members is 1 and the type mapping of active property is set to @vocab, return the result of using the IRI compaction algorithm, passing active context, inverse context, the value of the @id member for var, and true for vocab.
    3. Otherwise, return value as is.
  5. Otherwise, if value has an @type member whose value matches the type mapping of active property, return the value associated with the @value member of value.
  6. Otherwise, if value has an @language member whose value matches the language mapping of active property, return the value associated with the @value member of value.
  7. Otherwise, if number members equals 1 and either the value of the @value member is not a string, or the active context has no default language, or the language mapping of active property is set to null,, return the value associated with the @value member.
  8. Otherwise, return value as is.

7. Flattening Algorithms §

7.1 Flattening Algorithm §

This algorithm flattens an expanded JSON-LD document by collecting all properties of a node in a single dictionary and labeling all blank nodes with blank node identifiers. This resulting uniform shape of the document, may drastically simplify the code required to process JSON-LD data in certain applications.

7.1.1 Overview §

This section is non-normative.

First, a node map is generated using the Node Map Generation algorithm which collects all properties of a node in a single dictionary. In the next step, the node map is converted to a JSON-LD document in flattened document form. Finally, if a context has been passed, the flattened document is compacted using the Compaction algorithm before being returned.

7.1.2 Algorithm §

The algorithm takes two input variables, an element to flatten and an optional context used to compact the flattened document. If not passed, context is set to null.

This algorithm generates new blank node identifiers and relabels existing blank node identifiers. The Generate Blank Node Identifier algorithm keeps an identifier map and a counter to ensure consistent relabeling and avoid collisions. Thus, before this algorithm is run, the identifier map is reset and the counter is initialized to 0.

  1. Initialize node map to a dictionary consisting of a single member whose key is @default and whose value is an empty dictionary.
  2. Perform the Node Map Generation algorithm, passing element and node map.
  3. Initialize default graph to the value of the @default member of node map, which is a dictionary representing the default graph.
  4. For each key-value pair graph name-graph in node map where graph name is not @default, perform the following steps:
    1. If default graph does not have a graph name member, create one and initialize its value to a dictionary consisting of an @id member whose value is set to graph name.
    2. Reference the value associated with the graph name member in default graph using the variable entry.
    3. Add an @graph member to entry and set it to an empty array.
    4. For each id-node pair in graph ordered by id, add node to the @graph member of entry, unless the only member of node is @id.
  5. Initialize an empty array flattened.
  6. For each id-node pair in default graph ordered by id, add node to flattened, unless the only member of node is @id.
  7. If context is null, return flattened.
  8. Otherwise, return the result of compacting flattened according the Compaction algorithm passing context ensuring that the compaction result has only the @graph keyword (or its alias) at the top-level other than @context, even if the context is empty or if there is only one element to put in the @graph array. This ensures that the returned document has a deterministic structure.

7.2 Node Map Generation §

This algorithm creates a dictionary node map holding an indexed representation of the graphs and nodes represented in the passed expanded document. All nodes that are not uniquely identified by an IRI get assigned a (new) blank node identifier. The resulting node map will have a member for every graph in the document whose value is another object with a member for every node represented in the document. The default graph is stored under the @default member, all other graphs are stored under their graph name.

7.2.1 Overview §

This section is non-normative.

The algorithm recursively runs over an expanded JSON-LD document to collect all properties of a node in a single dictionary. The algorithm constructs a dictionary node map whose keys represent the graph names used in the document (the default graph is stored under the key @default) and whose associated values are dictionaries which index the nodes in the graph. If a property's value is a node object, it is replaced by a node object consisting of only an @id member. If a node object has no @id member or it is identified by a blank node identifier, a new blank node identifier is generated. This relabeling of blank node identifiers is also done for properties and values of @type.

7.2.2 Algorithm §

The algorithm takes as input an expanded JSON-LD document element and a reference to a dictionary node map. Furthermore it has the optional parameters active graph (which defaults to @default), an active subject, active property, and a reference to a dictionary list. If not passed, active subject, active property, and list are set to null.

  1. If element is an array, process each item in element as follows and then return:
    1. Run this algorithm recursively by passing item for element, node map, active graph, active subject, active property, and list.
  2. Otherwise element is a dictionary. Reference the dictionary which is the value of the active graph member of node map using the variable graph. If the active subject is null, set node to null otherwise reference the active subject member of graph using the variable node.
  3. If element has an @type member, perform for each item the following steps:
    1. If item is a blank node identifier, replace it with a newly generated blank node identifier passing item for identifier.
  4. If element has an @value member, perform the following steps:
    1. If list is null:
      1. If node does not have an active property member, create one and initialize its value to an array containing element.
      2. Otherwise, compare element against every item in the array associated with the active property member of node. If there is no item equivalent to element, append element to the array. Two dictionaries are considered equal if they have equivalent key-value pairs.
    2. Otherwise, append element to the @list member of list.
  5. Otherwise, if element has an @list member, perform the following steps:
    1. Initialize a new dictionary result consisting of a single member @list whose value is initialized to an empty array.
    2. Recursively call this algorithm passing the value of element's @list member for element, active graph, active subject, active property, and result for list.
    3. Append result to the value of the active property member of node.
  6. Otherwise element is a node object, perform the following steps:
    1. If element has an @id member, set id to its value and remove the member from element. If id is a blank node identifier, replace it with a newly generated blank node identifier passing id for identifier.
    2. Otherwise, set id to the result of the Generate Blank Node Identifier algorithm passing null for identifier.
    3. If graph does not contain a member id, create one and initialize its value to a dictionary consisting of a single member @id whose value is id.
    4. Reference the value of the id member of graph using the variable node.
    5. If active subject is a dictionary, a reverse property relationship is being processed. Perform the following steps:
      1. If node does not have an active property member, create one and initialize its value to an array containing active subject.
      2. Otherwise, compare active subject against every item in the array associated with the active property member of node. If there is no item equivalent to active subject, append active subject to the array. Two dictionaries are considered equal if they have equivalent key-value pairs.
    6. Otherwise, if active property is not null, perform the following steps:
      1. Create a new dictionary reference consisting of a single member @id whose value is id.
      2. If list is null:
        1. If node does not have an active property member, create one and initialize its value to an array containing reference.
        2. Otherwise, compare reference against every item in the array associated with the active property member of node. If there is no item equivalent to reference, append reference to the array. Two dictionaries are considered equal if they have equivalent key-value pairs.
      3. Otherwise, append reference to the @list member of list.
    7. If element has an @type key, append each item of its associated array to the array associated with the @type key of node unless it is already in that array. Finally remove the @type member from element.
    8. If element has an @index member, set the @index member of node to its value. If node has already an @index member with a different value, a conflicting indexes error has been detected and processing is aborted. Otherwise, continue by removing the @index member from element.
    9. If element has an @reverse member:
      1. Create a dictionary referenced node with a single member @id whose value is id.
      2. Set reverse map to the value of the @reverse member of element.
      3. For each key-value pair property-values in reverse map:
        1. For each value of values:
          1. Recursively invoke this algorithm passing value for element, node map, active graph, referenced node for active subject, and property for active property. Passing a dictionary for active subject indicates to the algorithm that a reverse property relationship is being processed.
      4. Remove the @reverse member from element.
    10. If element has an @graph member, recursively invoke this algorithm passing the value of the @graph member for element, node map, and id for active graph before removing the @graph member from element.
    11. Finally, for each key-value pair property-value in element ordered by property perform the following steps:
      1. If property is a blank node identifier, replace it with a newly generated blank node identifier passing property for identifier.
      2. If node does not have a property member, create one and initialize its value to an empty array.
      3. Recursively invoke this algorithm passing value for element, node map, active graph, id for active subject, and property for active property.

7.3 Generate Blank Node Identifier §

This algorithm is used to generate new blank node identifiers or to relabel an existing blank node identifier to avoid collision by the introduction of new ones.

7.3.1 Overview §

This section is non-normative.

The simplest case is if there exists already a blank node identifier in the identifier map for the passed identifier, in which case it is simply returned. Otherwise, a new blank node identifier is generated by concatenating the string _:b and the counter. If the passed identifier is not null, an entry is created in the identifier map associating the identifier with the blank node identifier. Finally, the counter is increased by one and the new blank node identifier is returned.

7.3.2 Algorithm §

The algorithm takes a single input variable identifier which may be null. Between its executions, the algorithm needs to keep an identifier map to relabel existing blank node identifiers consistently and a counter to generate new blank node identifiers. The counter is initialized to 0 by default.

  1. If identifier is not null and has an entry in the identifier map, return the mapped identifier.
  2. Otherwise, generate a new blank node identifier by concatenating the string _:b and counter.
  3. Increment counter by 1.
  4. If identifier is not null, create a new entry for identifier in identifier map and set its value to the new blank node identifier.
  5. Return the new blank node identifier.

7.4 Merge Node Maps §

This algorithm creates a new map of subjects to nodes using all graphs contained in the graph map created using the Node Map Generation algorithm to create merged node objects containing information defined for a given subject in each graph contained in the node map.

  1. Create result as an empty dictionary
  2. For each graph name and node map in graph map and for each id and node in node map:
    1. Set merged node to the value for id in result, initializing it with a new dictionary consisting of a single member @id whose value is id, if it does not exist.
    2. For each property and values in node:
      1. If property is a keyword, add property and values to merged node.
      2. Otherwise, merge each element from values into the values for property in merged node, initializing it to an empty array if necessary.
  3. Return result.

8. RDF Serialization/Deserialization Algorithms §

This section describes algorithms to deserialize a JSON-LD document to an RDF dataset and vice versa. The algorithms are designed for in-memory implementations with random access to dictionary elements.

Throughout this section, the following vocabulary prefixes are used in compact IRIs:

Prefix IRI
rdf http://www.w3.org/1999/02/22-rdf-syntax-ns#
rdfs http://www.w3.org/2000/01/rdf-schema#
xsd http://www.w3.org/2001/XMLSchema#

8.1 Deserialize JSON-LD to RDF algorithm §

This algorithm deserializes a JSON-LD document to an RDF dataset. Please note that RDF does not allow a blank node to be used as a property, while JSON-LD does. Therefore, by default RDF triples that would have contained blank nodes as properties are discarded when interpreting JSON-LD as RDF.

8.1.1 Overview §

This section is non-normative.

The JSON-LD document is expanded and converted to a node map using the Node Map Generation algorithm. This allows each graph represented within the document to be extracted and flattened, making it easier to process each node object. Each graph from the node map is processed to extract RDF triple, to which any (non-default) graph name is applied to create an RDF dataset. Each node object in the node map has an @id member which corresponds to the RDF subject, the other members represent RDF predicates. Each member value is either an IRI or blank node identifier or can be transformed to an RDF literal to generate an RDF triple. Lists are transformed into an RDF collection using the List to RDF Conversion algorithm.

8.1.2 Algorithm §

The algorithm takes a JSON-LD document element and returns an RDF dataset. Unless the produceGeneralizedRdf option is set to true, RDF triple containing a blank node predicate are excluded from output.

This algorithm generates new blank node identifiers and relabels existing blank node identifiers. The Generate Blank Node Identifier algorithm keeps an identifier map and a counter to ensure consistent relabeling and avoid collisions. Thus, before this algorithm is run, the identifier map is reset and the counter is initialized to 0.

  1. Expand element according to the Expansion algorithm.
  2. Generate a node map according to the Node Map Generation algorithm.
  3. Initialize an empty RDF dataset dataset.
  4. For each graph name and graph in node map ordered by graph name:
    1. If graph name is a relative IRI, continue with the next graph name-graph pair.
    2. Initialize triples as an empty array.
    3. For each subject and node in graph ordered by subject:
      1. If subject is a relative IRI, continue with the next subject-node pair.
      2. For each property and values in node ordered by property:
        1. If property is @type, then for each type in values, append a triple composed of subject, rdf:type, and type to triples.
        2. Otherwise, if property is a keyword continue with the next property-values pair.
        3. Otherwise, if property is a blank node identifier and the produceGeneralizedRdf option is not true, continue with the next property-values pair.
        4. Otherwise, if property is a relative IRI, continue with the next property-values pair.
        5. Otherwise, property is an absolute IRI or blank node identifier. For each item in values:
          1. If item is a list object, initialize list triples as an empty array and list head to the result of the List Conversion algorithm, passing the value associated with the @list key from item and list triples. Append first a triple composed of subject, property, and list head to triples and finally append all triples from list triples to triples.
          2. Otherwise, item is a value object or a node object. Append a triple composed of subject, property, and the result of using the Object to RDF Conversion algorithm passing item to triples, unless the result is null, indicating a relative IRI that has to be ignored.
    4. If graph name is @default, add triples to the default graph in dataset.
    5. Otherwise, create a named graph in dataset composed of graph name and add triples.
  5. Return dataset.

8.2 Object to RDF Conversion §

This algorithm takes a node object or value object and transforms it into an RDF resource to be used as the object of an RDF triple. If a node object containing a relative IRI is passed to the algorithm, null is returned which then causes the resulting RDF triple to be ignored.

8.2.1 Overview §

This section is non-normative.

Value objects are transformed to RDF literals as described in section 8.6 Data Round Tripping whereas node objects are transformed to IRIs, blank node identifiers, or null.

8.2.2 Algorithm §

The algorithm takes as its sole argument item which MUST be either a value object or node object.

  1. If item is a node object and the value of its @id member is a relative IRI, return null.
  2. If item is a node object, return the IRI or blank node identifier associated with its @id member.
  3. Otherwise, item is a value object. Initialize value to the value associated with the @value member in item.
  4. Initialize datatype to the value associated with the @type member of item or null if item does not have such a member.
  5. If value is true or false, set value to the string true or false which is the canonical lexical form as described in section 8.6 Data Round Tripping If datatype is null, set it to xsd:boolean.
  6. Otherwise, if value is a number with a non-zero fractional part (the result of a modulo‑1 operation) or value is a number and datatype equals xsd:double, convert value to a string in canonical lexical form of an xsd:double as defined in [XMLSCHEMA11-2] and described in section 8.6 Data Round Tripping. If datatype is null, set it to xsd:double.
  7. Otherwise, if value is a number with no non-zero fractional part (the result of a modulo‑1 operation) or value is a number and datatype equals xsd:integer, convert value to a string in canonical lexical form of an xsd:integer as defined in [XMLSCHEMA11-2] and described in section 8.6 Data Round Tripping. If datatype is null, set it to xsd:integer.
  8. Otherwise, if datatype is null, set it to xsd:string or rdf:langString, depending on if item has an @language member.
  9. Initialize literal as an RDF literal using value and datatype. If item has an @language member, add the value associated with the @language key as the language tag of literal.
  10. Return literal.

8.3 List to RDF Conversion §

List Conversion is the process of taking a list object and transforming it into an RDF collection as defined in RDF Semantics [RDF11-MT].

8.3.1 Overview §

This section is non-normative.

For each element of the list a new blank node identifier is allocated which is used to generate rdf:first and rdf:rest ABBR. The algorithm returns the list head, which is either the first allocated blank node identifier or rdf:nil if the list is empty. If a list element represents a relative IRI, the corresponding rdf:first triple is omitted.

8.3.2 Algorithm §

The algorithm takes two inputs: an array list and an empty array list triples used for returning the generated triples.

  1. If list is empty, return rdf:nil.
  2. Otherwise, create an array bnodes composed of a newly generated blank node identifier for each entry in list.
  3. Initialize an empty array list triples.
  4. For each pair of subject from bnodes and item from list:
    1. Initialize object to the result of using the Object to RDF Conversion algorithm passing item to list triples.
    2. Unless object is null, append a triple composed of subject, rdf:first, and object.
    3. Set rest as the next entry in bnodes, or if that does not exist, rdf:nil. Append a triple composed of subject, rdf:rest, and rest to list triples.
  5. Return the first blank node from bnodes or rdf:nil if bnodes is empty.

8.4 Serialize RDF as JSON-LD Algorithm §

This algorithm serializes an RDF dataset consisting of a default graph and zero or more named graphs into a JSON-LD document.

In the RDF abstract syntax, RDF literals have a lexical form, as defined in [RDF11-CONCEPTS]. The form of these literals is used when creating JSON-LD values based on these literals.

8.4.1 Overview §

This section is non-normative.

Iterate through each graph in the dataset, converting each RDF collection into a list and generating a JSON-LD document in expanded form for all RDF literals, IRIs and blank node identifiers. If the use native types flag is set to true, RDF literals with a datatype IRI that equals xsd:integer or xsd:double are converted to a JSON numbers and RDF literals with a datatype IRI that equals xsd:boolean are converted to true or false based on their lexical form as described in section 8.6 Data Round Tripping. Unless the use rdf:type flag is set to true, rdf:type predicates will be serialized as @type as long as the associated object is either an IRI or blank node identifier.

8.4.2 Algorithm §

The algorithm takes one required and two optional inputs: an RDF dataset dataset and the two flags use native types and use rdf:type that both default to false.

  1. Initialize default graph to an empty dictionary.
  2. Initialize graph map to a dictionary consisting of a single member @default whose value references default graph.
  3. Initialize node usage map to an empty dictionary.
  4. For each graph in dataset:
    1. If graph is the default graph, set name to @default, otherwise to the graph name associated with graph.
    2. If graph map has no name member, create one and set its value to an empty dictionary.
    3. If graph is not the default graph and default graph does not have a name member, create such a member and initialize its value to a new dictionary with a single member @id whose value is name.
    4. Reference the value of the name member in graph map using the variable node map.
    5. For each RDF triple in graph consisting of subject, predicate, and object:
      1. If node map does not have a subject member, create one and initialize its value to a new dictionary consisting of a single member @id whose value is set to subject.
      2. Reference the value of the subject member in node map using the variable node.
      3. If object is an IRI or blank node identifier, and node map does not have an object member, create one and initialize its value to a new dictionary consisting of a single member @id whose value is set to object.
      4. If predicate equals rdf:type, the use rdf:type flag is not true, and object is an IRI or blank node identifier, append object to the value of the @type member of node; unless such an item already exists. If no such member exists, create one and initialize it to an array whose only item is object. Finally, continue to the next RDF triple.
      5. Set value to the result of using the RDF to Object Conversion algorithm, passing object and use native types.
      6. If node does not have an predicate member, create one and initialize its value to an empty array.
      7. If there is no item equivalent to value in the array associated with the predicate member of node, append a reference to value to the array. Two JSON objects are considered equal if they have equivalent key-value pairs.
      8. If object is a blank node identifier or IRI, it might represent the list node:
        1. If the object member of node usage map does not exist, initialize it to a new empty array.
        2. Append the value of the @id member of node to the object member of node usage map.
        3. If the object member of node map has no usages member, create one and initialize it to an empty array.
        4. Reference the usages member of the object member of node map using the variable usages.
        5. Append a new dictionary consisting of three members, node, property, and value to the usages array. The node member is set to a reference to node, property to predicate, and value to a reference to value.
  5. For each name and graph object in graph map:
    1. If graph object has no rdf:nil member, continue with the next name-graph object pair as the graph does not contain any lists that need to be converted.
    2. Initialize nil to the value of the rdf:nil member of graph object.
    3. For each item usage in the usages member of nil, perform the following steps:
      1. Initialize node to the value of the value of the node member of usage, property to the value of the property member of usage, and head to the value of the value member of usage.
      2. Initialize two empty arrays list and list nodes.
      3. While property equals rdf:rest, the value of the @id member of node is a blank node identifier, the array value of the member of node usage map associated with the @id member of node has only one member, the value associated to the usages member of node has exactly 1 entry, node has a rdf:first and rdf:rest property, both of which have as value an array consisting of a single element, and node has no other members apart from an optional @type member whose value is an array with a single item equal to rdf:List, node represents a well-formed list node. Perform the following steps to traverse the list backwards towards its head:
        1. Append the only item of rdf:first member of node to the list array.
        2. Append the value of the @id member of node to the list nodes array.
        3. Initialize node usage to the only item of the usages member of node.
        4. Set node to the value of the node member of node usage, property to the value of the property member of node usage, and head to the value of the value member of node usage.
        5. If the @id member of node is an IRI instead of a blank node identifier, exit the while loop.
      4. If property equals rdf:first, i.e., the detected list is nested inside another list
        1. and the value of the @id of node equals rdf:nil, i.e., the detected list is empty, continue with the next usage item. The rdf:nil node cannot be converted to a list object as it would result in a list of lists, which isn't supported.
        2. Otherwise, the list consists of at least one item. We preserve the head node and transform the rest of the linked list to a list object.
        3. Set head id to the value of the @id member of head.
        4. Set head to the value of the head id member of graph object so that all it's properties can be accessed.
        5. Then, set head to the only item in the value of the rdf:rest member of head.
        6. Finally, remove the last item of the list array and the last item of the list nodes array.
      5. Remove the @id member from head.
      6. Reverse the order of the list array.
      7. Add an @list member to head and initialize its value to the list array.
      8. For each item node id in list nodes, remove the node id member from graph object.
  6. Initialize an empty array result.
  7. For each subject and node in default graph ordered by subject:
    1. If graph map has a subject member:
      1. Add an @graph member to node and initialize its value to an empty array.
      2. For each key-value pair s-n in the subject member of graph map ordered by s, append n to the @graph member of node after removing its usages member, unless the only remaining member of n is @id.
    2. Append node to result after removing its usages member, unless the only remaining member of node is @id.
  8. Return result.

8.5 RDF to Object Conversion §

This algorithm transforms an RDF literal to a JSON-LD value object and a RDF blank node or IRI to an JSON-LD node object.

8.5.1 Overview §

This section is non-normative.

RDF literals are transformed to value objects whereas IRIs and blank node identifiers are transformed to node objects. If the use native types flag is set to true, RDF literals with a datatype IRI that equals xsd:integer or xsd:double are converted to a JSON numbers and RDF literals with a datatype IRI that equals xsd:boolean are converted to true or false based on their lexical form as described in section 8.6 Data Round Tripping.

8.5.2 Algorithm §

This algorithm takes two required inputs: a value to be converted to a dictionary and a flag use native types.

  1. If value is an IRI or a blank node identifier, return a new dictionary consisting of a single member @id whose value is set to value.
  2. Otherwise value is an RDF literal:
    1. Initialize a new empty dictionary result.
    2. Initialize converted value to value.
    3. Initialize type to null
    4. If use native types is true
      1. If the datatype IRI of value equals xsd:string, set converted value to the lexical form of value.
      2. Otherwise, if the datatype IRI of value equals xsd:boolean, set converted value to true if the lexical form of value matches true, or false if it matches false. If it matches neither, set type to xsd:boolean.
      3. Otherwise, if the datatype IRI of value equals xsd:integer or xsd:double and its lexical form is a valid xsd:integer or xsd:double according [XMLSCHEMA11-2], set converted value to the result of converting the lexical form to a JSON number.
    5. Otherwise, if value is a language-tagged string add a member @language to result and set its value to the language tag of value.
    6. Otherwise, set type to the datatype IRI of value, unless it equals xsd:string which is ignored.
    7. Add a member @value to result whose value is set to converted value.
    8. If type is not null, add a member @type to result whose value is set to type.
    9. Return result.

8.6 Data Round Tripping §

When deserializing JSON-LD to RDF JSON-native numbers are automatically type-coerced to xsd:integer or xsd:double depending on whether the number has a non-zero fractional part or not (the result of a modulo‑1 operation), the boolean values true and false are coerced to xsd:boolean, and strings are coerced to xsd:string. The numeric or boolean values themselves are converted to canonical lexical form, i.e., a deterministic string representation as defined in [XMLSCHEMA11-2].

The canonical lexical form of an integer, i.e., a number with no non-zero fractional part or a number coerced to xsd:integer, is a finite-length sequence of decimal digits (0-9) with an optional leading minus sign; leading zeros are prohibited. In JavaScript, implementers can use the following snippet of code to convert an integer to canonical lexical form:

Example 20: Sample integer serialization implementation in JavaScript
(value).toFixed(0).toString()

The canonical lexical form of a double, i.e., a number with a non-zero fractional part or a number coerced to xsd:double, consists of a mantissa followed by the character E, followed by an exponent. The mantissa is a decimal number and the exponent is an integer. Leading zeros and a preceding plus sign (+) are prohibited in the exponent. If the exponent is zero, it is indicated by E0. For the mantissa, the preceding optional plus sign is prohibited and the decimal point is required. Leading and trailing zeros are prohibited subject to the following: number representations must be normalized such that there is a single digit which is non-zero to the left of the decimal point and at least a single digit to the right of the decimal point unless the value being represented is zero. The canonical representation for zero is 0.0E0. xsd:double's value space is defined by the IEEE double-precision 64-bit floating point type [IEEE-754-2008] whereas the value space of JSON numbers is not specified; when deserializing JSON-LD to RDF the mantissa is rounded to 15 digits after the decimal point. In JavaScript, implementers can use the following snippet of code to convert a double to canonical lexical form:

Example 21: Sample floating point number serialization implementation in JavaScript
(value).toExponential(15).replace(/(\d)0*e\+?/,'$1E')

The canonical lexical form of the boolean values true and false are the strings true and false.

When JSON-native numbers are deserialized to RDF, lossless data round-tripping cannot be guaranteed, as rounding errors might occur. When serializing RDF as JSON-LD, similar rounding errors might occur. Furthermore, the datatype or the lexical representation might be lost. An xsd:double with a value of 2.0 will, e.g., result in an xsd:integer with a value of 2 in canonical lexical form when converted from RDF to JSON-LD and back to RDF. It is important to highlight that in practice it might be impossible to losslessly convert an xsd:integer to a number because its value space is not limited. While the JSON specification [RFC7159] does not limit the value space of numbers either, concrete implementations typically do have a limited value space.

To ensure lossless round-tripping the Serialize RDF as JSON-LD algorithm specifies a use native types flag which controls whether RDF literals with a datatype IRI equal to xsd:integer, xsd:double, or xsd:boolean are converted to their JSON-native counterparts. If the use native types flag is set to false, all literals remain in their original string representation.

Some JSON serializers, such as PHP's native implementation in some versions, backslash-escape the forward slash character. For example, the value http://example.com/ would be serialized as http:\/\/example.com\/. This is problematic as other JSON parsers might not understand those escaping characters. There is no need to backslash-escape forward slashes in JSON-LD. To aid interoperability between JSON-LD processors, forward slashes MUST NOT be backslash-escaped.

9. The Application Programming Interface §

This API provides a clean mechanism that enables developers to convert JSON-LD data into a variety of output formats that are often easier to work with.

The JSON-LD API uses Promises to represent the result of the various asynchronous operations. Promises are defined in [ECMASCRIPT-6.0]. General use within specifications can be found in [promises-guide].

9.1 The JsonLdProcessor Interface §

The JsonLdProcessor interface is the high-level programming structure that developers use to access the JSON-LD transformation methods.

It is important to highlight that implementations do not modify the input parameters. If an error is detected, the Promise is rejected passing a JsonLdError with the corresponding error code and processing is stopped.

If the documentLoader option is specified, it is used to dereference remote documents and contexts. The documentUrl in the returned RemoteDocument is used as base IRI and the contextUrl is used instead of looking at the HTTP Link Header directly. For the sake of simplicity, none of the algorithms in this document mention this directly.

[Constructor]
interface JsonLdProcessor {
    static Promise<JsonLdDictionary>           compact(JsonLdInput input,
                                                       JsonLdContext context,
                                                       optional JsonLdOptions? options);
    static Promise<sequence<JsonLdDictionary>> expand(JsonLdInput input,
                                                      optional JsonLdOptions? options);
    static Promise<JsonLdDictionary>           flatten(JsonLdInput input,
                                                       optional JsonLdContext? context,
                                                       optional JsonLdOptions? options);
};
compact

Compacts the given input using the context according to the steps in the Compaction algorithm:

  1. Create a new Promise promise and return it. The following steps are then executed asynchronously.
  2. Set expanded input to the result of using the expand method using input and options.
  3. If context is a dictionary having an @context member, set context to that member's value, otherwise to context.
  4. Initialize an active context using context; the base IRI is set to the base option from options, if set; otherwise, if the compactToRelative option is true, to the IRI of the currently being processed document, if available; otherwise to null.
  5. Set compacted output to the result of using the Compaction algorithm, using active context, an empty dictionary as inverse context, null as property, expanded input as element, and if passed, the compactArrays flag in options.
  6. Fulfill the promise passing compacted output. transforming compacted output from the internal representation to a JSON serialization.
input
The dictionary, array of dictionaries to perform the compaction upon or an IRI referencing the JSON-LD document to compact.
context
The context to use when compacting the input; it can be specified by using a dictionary, an IRI, or an array consisting of dictionaries and IRIs.
options
A set of options to configure the algorithms. This allows, e.g., to set the input document's base IRI.
expand

Expands the given input according to the steps in the Expansion algorithm:

  1. Create a new Promise promise and return it. The following steps are then executed asynchronously.
  2. If the passed input is a string representing the IRI of a remote document, dereference it. If the retrieved document's content type is neither application/json, nor application/ld+json, nor any other media type using a +json suffix as defined in [RFC6839], reject the promise passing an loading document failed error.
  3. Initialize a new empty active context. The base IRI of the active context is set to the IRI of the currently being processed document, if available; otherwise to null. If set, the base option from options overrides the base IRI.
  4. If an expandContext option has been passed, update the active context using the Context Processing algorithm, passing the expandContext as local context. If expandContext is a dictionary having an @context member, pass that member's value instead.
  5. Once input has been retrieved, the response has an HTTP Link Header [RFC5988] using the http://www.w3.org/ns/json-ld#context link relation and a content type of application/json or any media type with a +json suffix as defined in [RFC6839] except application/ld+json, update the active context using the Context Processing algorithm, passing the context referenced in the HTTP Link Header as local context. The HTTP Link Header is ignored for documents served as application/ld+json If multiple HTTP Link Headers using the http://www.w3.org/ns/json-ld#context link relation are found, the promise is rejected with a JsonLdError whose code is set to multiple context link headers and processing is terminated.
  6. If necessary, transform input into the internal representation. If input cannot be transformed to the internal representation, reject promise passing a loading document failed error.
  7. Set expanded output to the result of using the Expansion algorithm, passing the active context and input as element, and, if the frameExpansion option is set, pass the frame expansion flag as true..
  8. Fulfill the promise passing expanded output. transforming expanded output from the internal representation to a JSON serialization.
input
The dictionary or array of dictionaries to perform the expansion upon or an IRI referencing the JSON-LD document to expand.
options
A set of options to configure the used algorithms such. This allows, e.g., to set the input document's base IRI.
flatten

Flattens the given input and compacts it using the passed context according to the steps in the Flattening algorithm:

  1. Create a new Promise promise and return it. The following steps are then executed asynchronously.
  2. Set expanded input to the result of using the expand method using input and options.
  3. If context is a dictionary having an @context member, set context to that member's value, otherwise to context.
  4. Initialize an active context using context; the base IRI is set to the base option from options, if set; otherwise, if the compactToRelative option is true, to the IRI of the currently being processed document, if available; otherwise to null.
  5. Initialize an empty identifier map and a counter (set to 0) to be used by the Generate Blank Node Identifier algorithm.
  6. Set flattened output to the result of using the Flattening algorithm, passing expanded input as element, active context, and if passed, the compactArrays flag in options (which is internally passed to the Compaction algorithm).
  7. Fulfill the promise passing flattened output. transforming flattened output from the internal representation to a JSON serialization.
input
The dictionary or array of dictionaries or an IRI referencing the JSON-LD document to flatten.
context
The context to use when compacting the flattened expanded input; it can be specified by using a dictionary, an IRI, or an array consisting of dictionaries and IRIs. If not passed or null is passed, the result will not be compacted but kept in expanded form.
options
A set of options to configure the used algorithms such. This allows, e.g., to set the input document's base IRI.
dictionary JsonLdDictionary {
};

The JsonLdDictionary is the definition of a dictionary used to contain arbitrary key/value pairs which are the result of parsing a JSON Object.

typedef (JsonLdDictionary or sequence<JsonLdDictionary> or USVString) JsonLdInput;

The JsonLdInput type is used to refer to an input value that that may be a dictionary, an array of dictionaries or a string representing an IRI which an be dereferenced to retrieve a valid JSON document.

typedef (JsonLdDictionary or USVString or sequence<(JsonLdDictionary or USVString)>) JsonLdContext;

The JsonLdContext type is used to refer to a value that that may be a dictionary, a string representing an IRI, or an array of dictionaries and strings.

9.2 The JsonLdOptions Type §

The JsonLdOptions type is used to pass various options to the JsonLdProcessor methods.

dictionary JsonLdOptions {
    USVString?                       base;
    boolean                          compactArrays = true;
    boolean                          compactToRelative = true;
    LoadDocumentCallback             documentLoader = null;
    (JsonLdDictionary? or USVString) expandContext = null;
    boolean                          frameExpansion = false;
    USVString                        processingMode = null;
    boolean                          produceGeneralizedRdf = true;
};
base
The base IRI to use when expanding or compacting the document. If set, this overrides the input document's IRI.
compactArrays
If set to true, the JSON-LD processor replaces arrays with just one element with that element during compaction. If set to false, all arrays will remain arrays even if they have just one element.
compactToRelative
Determines if IRIs are compacted relative to the base option or document location when compacting.
documentLoader
The callback of the loader to be used to retrieve remote documents and contexts. If specified, it is used to retrieve remote documents and contexts; otherwise, if not specified, the processor's built-in loader is used.
expandContext
A context that is used to initialize the active context when expanding a document.
frameExpansion
Enables special frame processing rules for the Expansion Algorithm.
processingMode
Sets the processing mode. If set to json-ld-1.0 or json-ld-1.1, the implementation must produce exactly the same results as the algorithms defined in this specification. If set to another value, the JSON-LD processor is allowed to extend or modify the algorithms defined in this specification to enable application-specific optimizations. The definition of such optimizations is beyond the scope of this specification and thus not defined. Consequently, different implementations may implement different optimizations. Developers must not define modes beginning with json-ld as they are reserved for future versions of this specification.
produceGeneralizedRdf
If set to true, the JSON-LD processor may emit blank nodes for triple predicates, otherwise they will be omitted.

9.3 Remote Document and Context Retrieval §

Users of an API implementation can utilize a callback to control how remote documents and contexts are retrieved. This section details the parameters of that callback and the data structure used to return the retrieved context.

9.3.1 LoadDocumentCallback §

The LoadDocumentCallback defines a callback that custom document loaders have to implement to be used to retrieve remote documents and contexts.

callback LoadDocumentCallback = Promise<USVString> (USVString url);
url
The URL of the remote document or context to load.

All errors result in the Promise being rejected with a JsonLdError whose code is set to loading document failed or multiple context link headers as described in the next section.

9.3.2 RemoteDocument §

The RemoteDocument type is used by a LoadDocumentCallback to return information about a remote document or context.

dictionary RemoteDocument {
    USVString contextUrl = null;
    USVString documentUrl;
    any       document;
};
contextUrl
If available, the value of the HTTP Link Header [RFC5988] using the http://www.w3.org/ns/json-ld#context link relation in the response. If the response's content type is application/ld+json, the HTTP Link Header is ignored. If multiple HTTP Link Headers using the http://www.w3.org/ns/json-ld#context link relation are found, the Promise of the LoadDocumentCallback is rejected with a JsonLdError whose code is set to multiple context link headers.
documentUrl
The final URL of the loaded document. This is important to handle HTTP redirects properly.
document
The retrieved document. This can either be the raw payload or the already parsed document.

9.4 Error Handling §

This section describes the datatype definitions used within the JSON-LD API for error handling.

9.4.1 JsonLdError §

The JsonLdError type is used to report processing errors.

dictionary JsonLdError {
    JsonLdErrorCode code;
    USVString?      message = null;
};
code
a string representing the particular error type, as described in the various algorithms in this document.
message
an optional error message containing additional debugging information. The specific contents of error messages are outside the scope of this specification.

9.4.2 JsonLdErrorCode §

The JsonLdErrorCode represents the collection of valid JSON-LD error codes.

enum JsonLdErrorCode {
    "colliding keywords",
    "compaction to list of lists",
    "conflicting indexes",
    "cyclic IRI mapping",
    "invalid @id value",
    "invalid @index value",
    "invalid @nest value",
    "invalid @prefix value",
    "invalid @reverse value",
    "invalid @version value",
    "invalid base IRI",
    "invalid container mapping",
    "invalid default language",
    "invalid IRI mapping",
    "invalid keyword alias",
    "invalid language map value",
    "invalid language mapping",
    "invalid language-tagged string",
    "invalid language-tagged value",
    "invalid local context",
    "invalid remote context",
    "invalid reverse property",
    "invalid reverse property map",
    "invalid reverse property value",
    "invalid scoped context",
    "invalid set or list object",
    "invalid term definition",
    "invalid type mapping",
    "invalid type value",
    "invalid typed value",
    "invalid value object",
    "invalid value object value",
    "invalid vocab mapping",
    "keyword redefinition",
    "list of lists",
    "loading document failed",
    "loading remote context failed",
    "multiple context link headers",
    "processing mode conflict",
    "recursive context inclusion"
};
colliding keywords
Two properties which expand to the same keyword have been detected. This might occur if a keyword and an alias thereof are used at the same time.
compaction to list of lists
The compacted document contains a list of lists as multiple lists have been compacted to the same term.
conflicting indexes
Multiple conflicting indexes have been found for the same node.
cyclic IRI mapping
A cycle in IRI mappings has been detected.
invalid @id value
An @id member was encountered whose value was not a string.
invalid @index value
An @index member was encountered whose value was not a string.
invalid @nest value
An invalid value for @nest has been found.
invalid @prefix value
An invalid value for @prefix has been found.
invalid @reverse value
An invalid value for an @reverse member has been detected, i.e., the value was not a dictionary.
invalid @version value
The @version key was used in a context with an out of range value.
invalid base IRI
An invalid base IRI has been detected, i.e., it is neither an absolute IRI nor null.
invalid container mapping
An @container member was encountered whose value was not one of the following strings: @list, @set, or @index.
invalid default language
The value of the default language is not a string or null and thus invalid.
invalid IRI mapping
A local context contains a term that has an invalid or missing IRI mapping.
invalid keyword alias
An invalid keyword alias definition has been encountered.
invalid language map value
An invalid value in a language map has been detected. It has to be a string or an array of strings.
invalid language mapping
An @language member in a term definition was encountered whose value was neither a string nor null and thus invalid.
invalid language-tagged string
A language-tagged string with an invalid language value was detected.
invalid language-tagged value
A number, true, or false with an associated language tag was detected.
invalid local context
In invalid local context was detected.
invalid remote context
No valid context document has been found for a referenced, remote context.
invalid reverse property
An invalid reverse property definition has been detected.
invalid reverse property map
An invalid reverse property map has been detected. No keywords apart from @context are allowed in reverse property maps.
invalid reverse property value
An invalid value for a reverse property has been detected. The value of an inverse property must be a node object.
invalid scoped context
The local context defined within a term definition is invalid.
invalid set or list object
A set object or list object with disallowed members has been detected.
invalid term definition
An invalid term definition has been detected.
invalid type mapping
An @type member in a term definition was encountered whose value could not be expanded to an absolute IRI.
invalid type value
An invalid value for an @type member has been detected, i.e., the value was neither a string nor an array of strings.
invalid typed value
A typed value with an invalid type was detected.
invalid value object
A value object with disallowed members has been detected.
invalid value object value
An invalid value for the @value member of a value object has been detected, i.e., it is neither a scalar nor null.
invalid vocab mapping
An invalid vocabulary mapping has been detected, i.e., it is neither an absolute IRI nor null.
keyword redefinition
A keyword redefinition has been detected.
list of lists
A list of lists was detected. List of lists are not supported in this version of JSON-LD due to the algorithmic complexity.
loading document failed
The document could not be loaded or parsed as JSON.
loading remote context failed
There was a problem encountered loading a remote context.
multiple context link headers
Multiple HTTP Link Headers [RFC5988] using the http://www.w3.org/ns/json-ld#context link relation have been detected.
processing mode conflict
An attempt was made to change the processing mode which is incompatible with the previous specified version.
recursive context inclusion
A cycle in remote context inclusions has been detected.

A. IDL Index §

This section is non-normative.

[Constructor]
interface JsonLdProcessor {
    static Promise<JsonLdDictionary>           compact(JsonLdInput input,
                                                       JsonLdContext context,
                                                       optional JsonLdOptions? options);
    static Promise<sequence<JsonLdDictionary>> expand(JsonLdInput input,
                                                      optional JsonLdOptions? options);
    static Promise<JsonLdDictionary>           flatten(JsonLdInput input,
                                                       optional JsonLdContext? context,
                                                       optional JsonLdOptions? options);
};
dictionary JsonLdDictionary {
};
typedef (JsonLdDictionary or sequence<JsonLdDictionary> or USVString) JsonLdInput;
typedef (JsonLdDictionary or USVString or sequence<(JsonLdDictionary or USVString)>) JsonLdContext;
dictionary JsonLdOptions {
    USVString?                       base;
    boolean                          compactArrays = true;
    boolean                          compactToRelative = true;
    LoadDocumentCallback             documentLoader = null;
    (JsonLdDictionary? or USVString) expandContext = null;
    boolean                          frameExpansion = false;
    USVString                        processingMode = null;
    boolean                          produceGeneralizedRdf = true;
};
callback LoadDocumentCallback = Promise<USVString> (USVString url);
dictionary RemoteDocument {
    USVString contextUrl = null;
    USVString documentUrl;
    any       document;
};
dictionary JsonLdError {
    JsonLdErrorCode code;
    USVString?      message = null;
};
enum JsonLdErrorCode {
    "colliding keywords",
    "compaction to list of lists",
    "conflicting indexes",
    "cyclic IRI mapping",
    "invalid @id value",
    "invalid @index value",
    "invalid @nest value",
    "invalid @prefix value",
    "invalid @reverse value",
    "invalid @version value",
    "invalid base IRI",
    "invalid container mapping",
    "invalid default language",
    "invalid IRI mapping",
    "invalid keyword alias",
    "invalid language map value",
    "invalid language mapping",
    "invalid language-tagged string",
    "invalid language-tagged value",
    "invalid local context",
    "invalid remote context",
    "invalid reverse property",
    "invalid reverse property map",
    "invalid reverse property value",
    "invalid scoped context",
    "invalid set or list object",
    "invalid term definition",
    "invalid type mapping",
    "invalid type value",
    "invalid typed value",
    "invalid value object",
    "invalid value object value",
    "invalid vocab mapping",
    "keyword redefinition",
    "list of lists",
    "loading document failed",
    "loading remote context failed",
    "multiple context link headers",
    "processing mode conflict",
    "recursive context inclusion"
};

B. Security Considerations §

Editor's note

Consider requirements from Self-Review Questionnaire: Security and Privacy.

C. Changes since 1.0 Recommendation of 16 January 2014 §

This section is non-normative.

D. Open Issues §

This section is non-normative.

The following is a list of issues open at the time of publication.

Issue 246: Ignoring semantically meaningless nestingapideferspec-designsyntax

Thanks for the great work with JSON-LD! However, when trying to use JSON-LD for to present data in the company I'm working in, I noticed the following missing feature:

FEATURE PROPOSAL: ABILITY TO DEFINE ANY KEY AS AN INDEX KEY

In addition to JSON-LD's existing index container structure, I propose that any key under a JSON-LD node could be defined as a index key.

This would help clustering data under a node into coder friendly logical groups without messing up the Linked Data interpretation with e.g. blank nodes. I encountered the need for this feature at our company where our problem is that the amount of attributes a single JSON-LD node can have can potentially be quite many, say, tens or hundreds of attributes.

As far as I know, this can not be currently done with JSON-LD without 1) ending up with blank nodes or 2) the need to create a deeper JSON structure by using a separate index term (using "@container":"@index") which then contains the data underneath.

In addition, if a single key could be defined as a index term, this would make it more flexible to attach the JSON-LD Linked Data interpretation to even a wider amount of existing JSON data, without having to change the structure of such data (and without ending up with e.g. lots of blank nodes).

DEFINING AN INDIVIDUAL INDEX KEY IN @context

The "@context" definition could be done e.g. using the existing reserved keyword "@index" in the following way:

"indexkey":"@index"

which should be interpreted in the following way: 1) the "indexkey" is an index key and should be skipped when traversing the JSON tree while doing the JSON-LD to RDF interpretation, 2) any data directly under the "indexkey" should be interpreted as data directly attached to the node of the indexkey (same RDF subject).

EXAMPLE

To give a full example, in the following a single key "labels" is defined as an index index key to help grouping the data into coder friendly logical groups without messing up the Linked Data interpretation):

{
  "@context": {
     "labels":"@index",
     "main_label":"http://example.org/my-schema#main_label",
     "other_label":"http://example.org/my-schema#other_label",
     "homepage":{ "@id":"http://example.org/my-schema#homepage", "@type":"@id"}
  },
  "@id":"http://example.org/myresource",
  "homepage": "http://example.org",
  "labels": {
     "main_label": "This is the main label for my resource",
     "other_label": "This is the other label"
  }
}

This example JSON-LD should generate the following RDF triplets:

<http://example.org/myresource> <http://example.org/my-schema#homepage> <http://example.org>.
<http://example.org/myresource> <http://example.org/my-schema#main_label> "This is the main label for my resource".
<http://example.org/myresource> <http://example.org/my-schema#other_label> "This is the other label".
Issue 333: Support JSON values that aren't mappedapideferspec-designsyntax

This has already been discussed several times usingvarious terms.. the most recent request has come from David Janes on the mailing list. The basic idea is to support JSON values/subtrees that aren't mapped to an IRI in the context. They should survive algorithmic transformations (basically without being touched at all).

Issue 338: Option to compact terms but not valuesapidefer

_This was raised by Fabian Steeg:_

The JSON-LD API document states: "Expansion has two important goals: removing any contextual information from the document, and ensuring all values are represented in a regular form."

Is there a way to achieve only the second goal, the regular form, but with compact terms? Using compaction with compactArrays=false is pretty close, but there is still at least one thing that is irregular and causing issues for me.

Given this input:

{
  "http://example.com/foo": "foo-value",
  "http://example.com/bar": {
    "@value": "bar-value",
    "@language": "en"
  },
  "@context": {
    "foo": "http://example.com/foo",
    "bar": "http://example.com/bar"
  }
}

I get this from compaction with compactArrays=false:

{
  "@graph": [{
    "foo": ["foo-value"],              <-- foo: array of strings
    "bar": [{                          <-- bar: array of objects
      "@language": "en",
      "@value": "bar-value"
    }]
  }],
  "@context": {
    "foo": "http://example.com/foo",
    "bar": "http://example.com/bar"
  }
}

But I'd like to get this (which is what expansion does to the values):

{
  "@graph": [{
    "foo": [{                          <-- both foo and bar:
      "@value" : "foo-value"               array of objects
    }],
    "bar": [{
      "@language": "en",
      "@value": "bar-value"
    }]
  }],
  "@context": {
    "foo": "http://example.com/foo",
    "bar": "http://example.com/bar"
  }
}

So I guess I'm looking for something like a compactValues=false option.

Is there some way to get this output?

Issue 357: Lists shared between graphs are not correctly serializedapispec-bug

_Reported by @afs:_

We are encountering an issue when converting RDF Datasets to JSON-LD.

The problem is with blank nodes that are shared between graphs and lists.

In TriG (yes, this is a synthetic reduced test case that captures a
smaller example that might appear for real):

# Bnode references across graph and lists
PREFIX :        <http://www.example.com/>
PREFIX rdf:     <http://www.w3.org/1999/02/22-rdf-syntax-ns#>

:G {
   # Written in short form it would be:
   # :z :q ("cell-A" "cell-B")
   # but we want to share the tail ("cell-B")

   :z :q _:z0 .

   _:z0   rdf:first "cell-A" .
   _:z0   rdf:rest  _:z1 .

   _:z1   rdf:first "cell-B" .
   _:z1   rdf:rest rdf:nil .
}

:G1 {
    # This references the tail  ("cell-B")
    :x :p _:z1 .
}

The triple in :G1 references into the list in :G.

But as we understand the conversion algorithm, section 4 only considers
each graph in turn and so does not see the cross graph sharing.

Is this a correct reading of the spec text?

Part 4 of the conversion algorithm has
"For each name and graph object in graph map: "

so 4.3.3.* walks back up the list in one graph only.

(Conversion generated by jsonld-java : it does not matter if compaction
is applied or not):

{
   "@graph" : [ {
     "@graph" : [ {
       "@id" : ":z",
       ":q" : {
         "@list" : [ "cell-A", "cell-B" ]
       }
     } ],
     "@id" : ":G"
   }, {
     "@graph" : [ {
       "@id" : ":x",
       ":p" : {
         "@id" : "_:b1"
       }
     } ],
     "@id" : ":G1"
   } ],
   "@context" : {
     "@base" : "http://www.example.com/",
     "" : "http://www.example.com/",
     "rdf" : "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   }
}

There is no _:b1 in :G to refer to because the algorith generated @list
and its implicit bNodes don't have labels.
This is a different dataset with no shared bNode.

If it is all the same graph (s/:G1/:G/), the RDF dataset structure is
correctly serialized.

Andy

Issue 368: JSON-LD 1.1 Feature Request: Object-level @languageapideferspec-designsyntax

See: digitalbazaar/jsonld.js#72

It would be helpful to have the ability to use @language within an object as a shorthand for "@context": {"@language": "..."} ... for instance... make:

{
  "@language": "en",
  "displayName": "foo"
}

equivalent to:

{
  "@context": {"@language": "en"},
  "displayName": "foo"
}
Issue 371: JSON-LD 1.1 Feature Request: New @label keywordapideferspec-designsyntax

In the spirit of "Labeling Everything" (http://patterns.dataincubator.org/book/label-everything.html) ... it would be worthwhile, IMO, for JSON-LD to provide a basic @Label keyword for use both in @context and nodes. It's largely syntactic sugar but would be useful.

For example:

{
  "@context": {
    "@label": "An Example Context",
    "displayName": "@label",
  },
  "displayName": "A Simple Label"
}

Which would expand to:

_:c14n0 <http://www.w3.org/2000/01/rdf-schema#label> "A Simple Label" .
Issue 397: JSON-LD 1.1 Feature Request: support @values for describing multidimensional containers (list of lists)apideferspec-designsyntax

Problem description §

Many JSON specs existed before JSON-LD. A couple of these specs may not be compatible with JSON-LD as they contain multidimensional containers, such as GeoJSON.

Example of a multidimensional array:

[ [3.1,51.06,30],
  [3.1,51.06,20] ]

This issue is a result from the discussion on the GeoJSON-LD repository: geojson/geojson-ld#32. If this issue will not get resolved, the GeoJSON-LD community would suggest creating custom JSON-LD parsers for JSON-LD dialects. This situation would be far from desirable.

Suggested solution §

Introduce a new @values keyword, which can be used to describe the values of a @set or a @list container in more detail.

When an array is given in the @values, then the precise amount of objects within this array corresponds with the array in the graph in this order.

When an object is given in the @values, each value of the array in the graph is mapped according to this template.

Example §

{
  "@context": {
     "coordinates": {
        "@id": "geojson:coordinates",
        "@container" : "@list",
        "@values" : {
           "@type" : "geojson:Coordinate",
           "@container" : "@set",
           "@values" : [
               {"@type" : "xsd:double", "@id":"geo:longitude"},
               {"@type" : "xsd:double", "@id":"geo:latitude"}
           ]
        }
     }
  },
  "@graph" : [{
   "@id" : "ex:LineString1",
    "coordinates" : [
          [
            3.1057405471801753,
            51.064216229943476
          ],
          [
            3.1056976318359375,
            51.063434090307574
          ]
    ]
  }]
}

Would transform to (and vice versa):

ex:LineString1 geojson:coordinates _:b0 .
_:b0 rdf:first _:b1 .
_:b1 a geojson:Coordinate ;
      geo:longitude "3.105740547180175E0"^^xsd:double ;
      geo:latitude "5.106421622994348E1"^^xsd:double .
_:b0 rdf:rest _:b2 .
_:b2 rdf:first a geojson:Coordinate ;
      geo:longitude "3.1056976318359375"^^xsd:double ;
      geo:latitude "51.063434090307574"^^xsd:double .
_:b2 rdf:rest rdf:nil .
Issue 402: Relax the colliding keywords constraint for @typeapideferspec-design

I want the following:

{
  "@context": {
    "type": "@type",
    "profile": "@type"
  },
  "type": "cov:Coverage",
  "profile": "cov:GridCoverage"
}

However this is not allowed. The playground says "Invalid JSON-LD syntax; colliding keywords detected".

However, this one works:

{
  "@context": {
    "type": {"@id": "rdf:type", "@type": "@id" },
    "profile": {"@id": "rdf:type", "@type": "@id" }
  },
  "type": "cov:Coverage",
  "profile": "cov:GridCoverage"
}

I understand that this restriction probably makes sense for other keywords, but could it do any harm for @type?

Issue 434: Streaming Profiles for JSON-LD to/from RDFapideferspec-design

There have been some discussions on what it would take to be able to do a streaming parse of JSON-LD into Quads, and similarly to generate compliant JSON-LD from a stream of quads. Describing these as some kind of a profile would be useful for implementations that expect to work in a streaming environment, when it's not feasible to work on an entire document basis.

As currently stated, the JSON-LD to RDF algorithm requires expanding the document and creating a node map. A profile of JSON-LD which used a flattened array of node objects, where each node object could be independently expanded and no flattening is required could facilitate deserializing an arbitrarily long JSON-LD source to Quads. (Some simplifying restrictions on shared lists may be necessary). Outer document is an object, containing @context and @graph only; obviously, this only will work for systems that can access key/values in order, and for systems that ensure that @context comes lexically before @graph in the output. Obviously, only implementations that can read and write JSON objects with key ordering intact will be able to take advantage of such streaming capability.

Fo serializing RDF to JSON-LD, expectations on the grouping of quads with the same graph name and subject are necessary to reduce serialization cost, and marshaling components of RDF Lists is likely not feasible. Even if graph name/subject grouping is not maintained in the input, the resulting output will still represent a valid JSON-LD document, although it may require flattening for further processing. (Many triple stores will, in fact, generate statements/quads properly grouped, so this is likely not an issue in real world applications).

Issue 460: "Stratified" or "Dictionaried" API featureapideferspec-design

Hi there,

I was looking for a way to access properties in a JSON-LD document based on triples (to patch the document). This would mean having a view which creates a dictionary for a given document. The term Normalisation is already used, but this approach would be close to the way https://github.com/paularmstrong/normalizr. D3 uses https://github.com/d3/d3-hierarchy/blob/master/README.md#stratify in a slightly different way but with the same general intent.

The goal would be to be able to address document values with this syntax stratified_doc[triple.subject][triple.predicate] or even better stratified[triple.graph][triple.subject][triple.predicate].

This could also be a @stratified parameter for expansion.

Example §

For a document:

{
  "@context": {
    "dc": "http://purl.org/dc/elements/1.1/",
    "ex": "http://example.org/vocab#",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "ex:contains": {
      "@type": "@id"
    }
  },
  "@id": "http://example.org/graph/0",
  "dc:creator": "Jane Doe",
  "@graph": [
    {
      "@id": "http://example.org/library",
      "@type": "ex:Library",
      "ex:contains": "http://example.org/library/the-republic"
    }
  ]
}

Such a stratified would therefore look like:

{
  "http://example.org/graph/0": {
   "http://example.org/library": {
      "@type": "http://example.org/vocab#Library",
      "http://example.org/vocab#contains": {
        "@id": "http://example.org/library/the-republic"
      }
    },
    "http://example.org/library/the-republic": {}
  },
  "@graph": {
    "http://example.org/graph/0": {
      "http://purl.org/dc/elements/1.1/creator": "Jane Doe"
    }
  }
}

This would therefore allow to do the following:

// Access a triple from the default graph
var creator = stratified['@graph']['http://example.org/graph/0']['http://purl.org/dc/elements/1.1/creator'];
// "Jane Doe"

// Access a triple in a named graph
var type = stratified['http://example.org/graph/0']['http://example.org/library']['@type'];
// "http://example.org/vocab#Library"

// Before submitting a document, mutate a property
stratified['http://example.org/graph/0']['http://example.org/library/the-republic']['@type'] = 'http://example.org/vocab#Book';

// Or using an immutable spread syntax approach
var new_doc = {
  ...stratified,
  'http://example.org/graph/0': {
    ...stratified['http://example.org/graph/0'],
    'http://example.org/library/the-republic' : {
      ...stratified['http://example.org/graph/0']['http://example.org/library/the-republic'],
      '@type': 'http://example.org/vocab#Book'
    }
  }
}
Issue 507: JSON-LD 1.1: method to require {"id": "uri"} resource compaction resultapidefer

Issue: The compaction algorithm prefers the most compact format, which for resources without relationships is a string containing the URI. This causes problems in systems that cannot handle arrays of mixed data types (for example ElasticSearch) when there are also resources that have relationships, resulting in both objects and strings in the same array.

For example:

"seeAlso": [
    "http://example.org/reference1",
    {"id": "http://example.org/reference2", "format": "text/html"}
  ]

would raise an error in Elastic.

Proposed solution: Provide a flag to the compaction algorithm to signal that the resulting JSON should always create objects for resources, even if there is only the URI available. This would instead render the example above as an array of objects:

"seeAlso": [
    {"id": "http://example.org/reference1"},
    {"id": "http://example.org/reference2", "format": "text/html"}
  ]
Issue 512: @type as @container:@set?apispec-design

The purpose of the @container:@set functionality (AFAIU) is to ensure that the output is consistent in shape. Thus if there can ever be multiple values, the structure is always an array.

There are two situations in which this functionality could be desirable but is currently not possible:

  1. @type As it's a keyword, we can only alias it (e.g. as type) but not define it to have @container:@set functionality. Meaning that there's a gotcha waiting to happen for ontologies that require or use multiple classes for a single resource instance. See playground
  2. @context Less useful, but @context will also compact to a single string/object when there might be multiple contexts. See playground

@context modifying itself seems particularly strange, but the inconsistency for @type seems solvable if the restrictions in its definition were loosened?

Issue 526: precedence of @vocab for compaction too strong?apideferspec-design

This is related to #235: When I have the following document:

{
  "@context": {
    "@vocab"  : "http://vocab.getty.edu/",
    "a"     : "http://vocab.getty.edu/aaaaaaaaaat/"
  },
  "@id" : "http://vocab.getty.edu/aaaaaaaaaat/5001065997",
  "@type": "http://vocab.getty.edu/aaaaaaaaaat/datatype"
}

By point 3 of the spec, because http://vocab.getty.edu/aaaaaaaaaat/5001065997 contains the value of @vocab, it gets compacted as aaaaaaaaaat/5001065997 without even looking at the prefixes. I think this is not reasonable, in this case a:5001065997 would look much nicer IMO.

Issue 530: Losing Last Element in RDF Listapiquestion

We have web application that needs to be able to modify RDF lists from a triple store and propagate the changes back. To do this, we are utilizing jsonld-java to serialize the RDF into JSON-LD, modifying it in the web app, and then sending it back to be deserialized and stored in the triple store. Originally, we were using blank nodes like the ones shown in Turtle below.

<http://example.com> <http://example.com/property> _:a .
_:a a <http://www.w3.org/1999/02/22-rdf-syntax-ns#List> ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "a" ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> _:b .
_:b a <http://www.w3.org/1999/02/22-rdf-syntax-ns#List> ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "b" ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> _:c .
_:c a <http://www.w3.org/1999/02/22-rdf-syntax-ns#List> ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "c" ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> <http://www.w3.org/1999/02/22-rdf-syntax-ns#nil> .

However, we discovered that blank node lists are collapsed during serialization thus losing all the blank node IDs.

[ {
  "@id" : "http://example.com",
  "http://example.com/property" : [ {
    "@list" : [ {
      "@value" : "a"
    }, {
      "@value" : "b"
    }, {
      "@value" : "c"
    } ]
  } ]
} ]

With blank node IDs removed, we are no longer able to reference the existing RDF in the triple store to perform updates when the lists are modified in the web-app without much more complex logic. To avoid this, we skolemized the blank node IDs into IRIs.

<http://example.com> <http://example.com/property> <urn:a> .
<urn:a> a <http://www.w3.org/1999/02/22-rdf-syntax-ns#List> ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "a" ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> <urn:b> .
<urn:b> a <http://www.w3.org/1999/02/22-rdf-syntax-ns#List> ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "b" ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> <urn:c> .
<urn:c> a <http://www.w3.org/1999/02/22-rdf-syntax-ns#List> ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> "c" ;
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> <http://www.w3.org/1999/02/22-rdf-syntax-ns#nil> .

However, when serializing the skolemized triples, the IRI for the last element in the RDF list is hidden, in this case urn:c. This leads to the same problem we were having when using blank node IDs.

[ {
  "@id" : "http://example.com",
  "http://example.com/property" : [ {
    "@id" : "urn:a"
  } ]
}, {
  "@id" : "urn:a",
  "@type" : [ "http://www.w3.org/1999/02/22-rdf-syntax-ns#List" ],
  "http://www.w3.org/1999/02/22-rdf-syntax-ns#first" : [ {
    "@value" : "a"
  } ],
  "http://www.w3.org/1999/02/22-rdf-syntax-ns#rest" : [ {
    "@id" : "urn:b"
  } ]
}, {
  "@id" : "urn:b",
  "@type" : [ "http://www.w3.org/1999/02/22-rdf-syntax-ns#List" ],
  "http://www.w3.org/1999/02/22-rdf-syntax-ns#first" : [ {
    "@value" : "b"
  } ],
  "http://www.w3.org/1999/02/22-rdf-syntax-ns#rest" : [ {
    "@list" : [ {
      "@value" : "c"
    } ]
  } ]
} ]

Issue #277 seems to be the point where the implementation changed from serializing lists in the manner we expect to this new compact way. Is there any way we can get around this so that the last blank node of a list is not collapsed?

Issue 542: Feature request: Could framing return properties in the order listed by the frame? apideferframing

Currently it appears that properties are sorted into alphabetical order after any JSON-LD operation (compaction, framing).

In the context of framing, this is sometimes a nice feature, since it means that after framing multiple input JSON files, the JSON data is at least in a consistent order.

I understand that ordering is semantically meaningless, but as framing exists to turn the graph (which could correspond to multiple different trees) into a predictable JSON tree as a convenience for developers, it seems natural to me that if an explicit ordering is given in the frame, that the algorithm would respect that order rather than alphabetize. For example, if my data is:

{
  "@context": "http://schema.org/",
  "@id": "document",
  "b": "text",
  "a": "more text"

}

Under the frame:

{
  "@context": "http://schema.org/",
  "@id":  "document",
  "b": {},
  "a": {}
}

(example in playground)

the returned document reverses the order of b and a (to be alphabetical), and not the order given in the frame. Framing is a really elegant way to specify the nesting order, but it would be nice for framing to also be able to dictate the ordering, so that the output data file really follows the exact structure of the given frame.

Related issue: there is no way to indicate that referenced nodes should occur before they are references (excluding circular references), which can be useful in streaming files. Having control of the node order via the frame would also give a mechanism to address that.

Hope this makes sense and apologies if I'm missing something fundamental here that makes alphabetizing the node order the only logical thing to do; or if I've misunderstood the expected behavior.

Issue 548: Use version 2.0 instead of 1.1apideferspec-designsyntax

Comments at TPAC suggested that as our work is a breaking change (causing 1.0 processors that are not 1.1 compatible to intentionally break when they see "@version": 1.1), semantic versioning would suggest that we use a major release number, rather than a minor number.

This could impact a potential WG, which may want to make further changes, and then be in the place of using either 2.1 or 3.0, which is odd given that the previous recommendation is 1.0.

In some situations it is important/necessary to include the base direction of a text, alongside its language; see the “Requirements for Language and Direction Metadata in Data Formats” for further details. In practice, in a vanilla JSON, it would require something like:

"title": [ { "value": "Moby Dick", "lang": "en" },
           { "value": "موبي ديك", "lang": "ar"  "dir": "rtl"}
         ]

(the example comes from that document).

At this moment, I believe the only way you can reasonably express that in JSON-LD is via cheating a bit:

"title": [ { "@value": "Moby Dick", "@language": "en" },
           { "@value": "موبي ديك",  "@language": "ar"  "dir": "rtl"}
         ]

and making sure that the dir term is not defined in the relevant @context so that, when generating the RDF output, that term is simply ignored. But that also means that there is no round-tripping, that term will disappear after expansion.

The difficulty lies in the RDF layer, in fact; RDF does not have any means (alas!) to express text direction. On the other hand, this missing feature is a general I18N problem whenever JSON-LD is used (there were issues when developing the Web Annotation Model, these issues are popping up in the Web Publication work, etc.).

Here is what I would propose as a non-complete solution

  1. Let us introduce a @dir term, alongside @language. This means this term can be used in place of dir above, ie, it is a bona-fide part of a string representation, and would therefore be kept in the compaction/expansion steps, can also be used for framing.
  2. In JSON-LD 1.1, @dir is ignored when transforming into RDF. I.e., only the language tag would be used.
  3. We may initiate some work in the RDF community to solve this issue. There may be several ways, each of them require the RDF community to chime in
    3.1. Define a mechanism of "parametrized" standard datatypes that represent a (language,direction) pair. One would then get something like[] ex:title "موبي ديك"^^rdf:internationalText(ar,rtl) ;
    3.2. Go for a "generalized" RDF where strings can also appear as subjects (that has been a matter of dispute for a long time...). That would give the possibility to add such attribute to texts like directions
    3.3. Some other mechanisms that I cannot think about
  4. In a future JSON-LD 1.* the @dir value can be properly mapped onto an RDF representing the right choices (if such choices are worked out)

Cc: @BigBlueHat @r12a

Issue 595: Native support for schema:ListItemapideferspec-designsyntax

Per a suggestion by @danbri, we may want to add a container type, similar to @list for encoding schema:ItemList serializations, when the values are schema:ListItem and order is set through schema:position. ItemList can be used with text values as well, but this is already reasonably supported natively.

Markup might look like the following:

{
  "@context": {
    "@vocab": "http://schema.org/",
    "itemListElement": {"@container": "@listItem"}
  },
  "@type": "ItemList",
  "@url": "http://en.wikipedia.org/wiki/Billboard_200",
  "name": "Top music artists",
  "description": "The artists with the most cumulative weeks at number one according to Billboard 200",
  "itemListElement": [
    {"@type": "MusicGroup", "name": "Beatles"},
    {"@type": "MusicGroup", "name": "Elvis Presley"},
    {"@type": "MusicGroup", "name": "Michael Jackson"},
    {"@type": "MusicGroup", "name": "Garth Brooks" }
  ]

This would expand to the following:

[
  {
    "@id": "http://en.wikipedia.org/wiki/Billboard_200",
    "@type": ["http://schema.org/ItemList"],
    "http://schema.org/description": [{
      "@value": "The artists with the most cumulative weeks at number one according to Billboard 200"
    }],
    "http://schema.org/itemListElement": [{
      "@type": ["http://schema.org/ListItem"],
      "http://schema.org/item": [{
        "@type": ["http://schema.org/MusicGroup"],
        "http://schema.org/name": [{"@value": "Beatles"}]
      }],
      "http://schema.org/position": [{"@value": 1}]
    },  {
      "@type": ["http://schema.org/ListItem"],
      "http://schema.org/item": [{
        "@type": ["http://schema.org/MusicGroup"],
        "http://schema.org/name": [{"@value": "Elvis Presley"}]
      }],
      "http://schema.org/position": [{"@value": 2}]
    }, {
      "@type": ["http://schema.org/ListItem"],
      "http://schema.org/item": [{
        "@type": ["http://schema.org/MusicGroup"],
        "http://schema.org/name": [{"@value": "Michael Jackson"}]
      }],
      "http://schema.org/position": [{"@value": 3}]
    }, {
      "@type": ["http://schema.org/ListItem"],
      "http://schema.org/item": [{
        "@type": ["http://schema.org/MusicGroup"],
        "http://schema.org/name": [{"@value": "Garth Brooks"}]
      }],
      "http://schema.org/position": [{"@value": 3}]
    }
  ],
  "http://schema.org/name": [{"@value": "Top music artists"}]
}]

Otherwise, it works like @list.

When compacting, the processor will re-order items based on position, and ignore any nextItem or previousItem entries.

Expansion shows 1-base position, but could be 0-base as well. Note that specific position values are lost when compacting, and duplicate values may lead to undefined relative ordering.

Issue 589: JSON-LD version on playgroundplayground

During the last meeting it was resolved to have one playground for 1.0 and 1.1 processing. Some notes on that related to jsonld.js:

From an ease of site development viewpoint, I think we should just put the most recent jsonld.js on the playground and add a UI control to pick the processingMode API option. Due to practicalities of jsonld.js not having a full correct 1.0 only lib, it seems not worth the effort to try and deal with this any other way. There are edge cases where a 1.1 lib in 1.0 mode will produce different results than a 1.0 lib. My guess is that in practice this really doesn't matter. Or in any case, is not worth handling on the playground.

E. Acknowledgements §

This section is non-normative.

A large amount of thanks goes out to the JSON-LD Community Group participants who worked through many of the technical issues on the mailing list and the weekly telecons - of special mention are Niklas Lindström, François Daoust, Lin Clark, and Zdenko 'Denny' Vrandečić. The editors would like to thank Mark Birbeck, who provided a great deal of the initial push behind the JSON-LD work via his work on RDFj. The work of Dave Lehn and Mike Johnson are appreciated for reviewing, and performing several implementations of the specification. Ian Davis is thanked for his work on RDF/JSON. Thanks also to Nathan Rixham, Bradley P. Allen, Kingsley Idehen, Glenn McDonald, Alexandre Passant, Danny Ayers, Ted Thibodeau Jr., Olivier Grisel, Josh Mandel, Eric Prud'hommeaux, David Wood, Guus Schreiber, Pat Hayes, Sandro Hawke, and Richard Cyganiak for their input on the specification.

F. References §

F.1 Normative references §

[BCP47]
Tags for Identifying Languages. A. Phillips; M. Davis. IETF. September 2009. IETF Best Current Practice. URL: https://tools.ietf.org/html/bcp47
[IEEE-754-2008]
IEEE 754-2008 Standard for Floating-Point Arithmetic. Institute of Electrical and Electronics Engineers. 2008. URL: http://standards.ieee.org/findstds/standard/754-2008.html
[JSON-LD]
JSON-LD 1.0. Manu Sporny; Gregg Kellogg; Markus Lanthaler. W3C. 16 January 2014. W3C Recommendation. URL: https://www.w3.org/TR/json-ld/
[JSON-LD11CG]
JSON-LD 1.1. Gregg Kellogg. W3C. CG Final. URL: https://www.w3.org/2018/jsonld-cg-reports/json-ld/
[RDF-CONCEPTS]
Resource Description Framework (RDF): Concepts and Abstract Syntax. Graham Klyne; Jeremy Carroll. W3C. 10 February 2004. W3C Recommendation. URL: https://www.w3.org/TR/rdf-concepts/
[RDF11-MT]
RDF 1.1 Semantics. Patrick Hayes; Peter Patel-Schneider. W3C. 25 February 2014. W3C Recommendation. URL: https://www.w3.org/TR/rdf11-mt/
[RFC2119]
Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. IETF. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119
[RFC3986]
Uniform Resource Identifier (URI): Generic Syntax. T. Berners-Lee; R. Fielding; L. Masinter. IETF. January 2005. Internet Standard. URL: https://tools.ietf.org/html/rfc3986
[RFC3987]
Internationalized Resource Identifiers (IRIs). M. Duerst; M. Suignard. IETF. January 2005. Proposed Standard. URL: https://tools.ietf.org/html/rfc3987
[RFC5988]
Web Linking. M. Nottingham. IETF. October 2010. Proposed Standard. URL: https://tools.ietf.org/html/rfc5988
[RFC7159]
The JavaScript Object Notation (JSON) Data Interchange Format. T. Bray, Ed.. IETF. March 2014. Proposed Standard. URL: https://tools.ietf.org/html/rfc7159
[XMLSCHEMA11-2]
W3C XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes. David Peterson; Sandy Gao; Ashok Malhotra; Michael Sperberg-McQueen; Henry Thompson; Paul V. Biron et al. W3C. 5 April 2012. W3C Recommendation. URL: https://www.w3.org/TR/xmlschema11-2/

F.2 Informative references §

[ECMASCRIPT-6.0]
ECMA-262 6th Edition, The ECMAScript 2015 Language Specification. Allen Wirfs-Brock. Ecma International. June 2015. Standard. URL: http://www.ecma-international.org/ecma-262/6.0/index.html
[JSON-LD-API]
JSON-LD 1.0 Processing Algorithms and API. Markus Lanthaler; Gregg Kellogg; Manu Sporny. W3C. 16 January 2014. W3C Recommendation. URL: https://www.w3.org/TR/json-ld-api/
[JSON-LD-TESTS]
JSON-LD 1.1 Test Suite. Gregg Kellogg. Linking Data in JSON Community Group. URL: https://json-ld.org/test-suite/
[JSON-LD11CG-API]
JSON-LD 1.1 Processing Algorithms and API. Gregg Kellogg. W3C. CG Final. URL: https://www.w3.org/2018/jsonld-cg-reports/json-ld-api/
[JSON-LD11CG-FRAMING]
JSON-LD 1.1 Framing. Gregg Kellogg. W3C. CG Final. URL: https://www.w3.org/2018/jsonld-cg-reports/json-ld-framing/
[promises-guide]
Writing Promise-Using Specifications. Domenic Denicola. W3C. 16 February 2016. Finding of the W3C TAG. URL: https://www.w3.org/2001/tag/doc/promises-guide
[RDF-SCHEMA]
RDF Schema 1.1. Dan Brickley; Ramanathan Guha. W3C. 25 February 2014. W3C Recommendation. URL: https://www.w3.org/TR/rdf-schema/
[RDF11-CONCEPTS]
RDF 1.1 Concepts and Abstract Syntax. Richard Cyganiak; David Wood; Markus Lanthaler. W3C. 25 February 2014. W3C Recommendation. URL: https://www.w3.org/TR/rdf11-concepts/
[RFC6839]
Additional Media Type Structured Syntax Suffixes. T. Hansen; A. Melnikov. IETF. January 2013. Informational. URL: https://tools.ietf.org/html/rfc6839
[TURTLE]
RDF 1.1 Turtle. Eric Prud'hommeaux; Gavin Carothers. W3C. 25 February 2014. W3C Recommendation. URL: https://www.w3.org/TR/turtle/
[WEBIDL]
Web IDL. Cameron McCormack; Boris Zbarsky; Tobie Langel. W3C. 15 December 2016. W3C Editor's Draft. URL: https://heycam.github.io/webidl/