W3C

JSON-LD Syntax 1.0

A Context-based JSON Serialization for Linking Data

W3C Working Editor's Draft 12 July 30 August 2012

This version:
http://www.w3.org/TR/2012/WD-json-ld-syntax-20120712/ http://dvcs.w3.org/hg/json-ld/raw-file/default/spec/ED/json-ld-syntax/20120830/index.html
Latest published version:
http://www.w3.org/TR/json-ld-syntax/
Latest editor's draft:
http://dvcs.w3.org/hg/json-ld/raw-file/default/spec/latest/json-ld-syntax/index.html
Editors:
Manu Sporny , Digital Bazaar
Gregg Kellogg , Kellogg Associates
Markus Lanthaler , Graz University of Technology
Authors:
Manu Sporny , Digital Bazaar
Dave Longley , Digital Bazaar
Gregg Kellogg , Kellogg Associates
Markus Lanthaler , Graz University of Technology
Mark Birbeck , Sidewinder Labs Backplane Ltd.

This document is also available in this non-normative format: diff to previous version


Abstract

JSON has proven to be a highly useful object serialization and messaging format. In an attempt to harmonize the representation of Linked Data in JSON, this specification outlines a common JSON representation format for expressing directed graphs; mixing both Linked Data and non-Linked Data in a single document.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This document has been under development for over 18 months in the JSON for Linking Data Community Group. The document has recently been transferred to the RDF Working Group for review, improvement, and publication along the Recommendation track. While this is a First Public Working Draft publication, the The specification has undergone significant development, review, and changes during the course of the last 18 months and is more mature than the First Public Working Draft status implies. months.

There are currently five interoperable implementations of this specification. There is a fairly complete test suite and a live JSON-LD editor that is capable of demonstrating the features described in this document. While development on implementations, the test suite and the live editor will continue, they are believed to be mature enough to be integrated into a non-production system at this point in time with the expectation that they could be used in a production system within the next year.

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

This document was published by the RDF Working Group as a First Public Working an Editor's Draft. This document is intended to become a W3C Recommendation. If you wish to make comments regarding this document, please send them to public-rdf-comments@w3.org ( subscribe , archives ). All feedback is welcome.

Publication as a Working an Editor's Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy . W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy .

Table of Contents

1. Introduction

This section is non-normative.

JSON, as specified in [ RFC4627 ], is a simple language for representing data on the Web. Linked Data is a technique for creating a network of inter-connected data across different Web documents and Web sites. A document in this data network is typically identified using an IRI (Internationalized Resource Identifier). A software program can typically follow an IRI just like you follow a URL by putting it into your browser's location bar. By following IRIs, a software program can find more information about the document and the thing s that the document describes. These things may also be identified using IRI s. The IRI allows a software program to start at one document and follow links to other documents or things in order to learn more about all of the documents and things described on the Web.

JSON-LD is designed as a lightweight syntax that can be used to express Linked Data . It is primarily intended to be a way to use Linked Data in Javascript and other Web-based programming environments. It is also useful when building inter-operable Web services and when storing Linked Data in JSON-based document storage engines. It is practical and designed to be as simple as possible, utilizing the large number of JSON parsers and libraries available today.

The syntax does not necessarily require applications to change their JSON, but allows one to easily add meaning by simply adding or referencing a context. The syntax is designed to not disturb already deployed systems running on JSON, but provide a smooth upgrade path from JSON to JSON-LD. Finally, the format is intended to be easy to parse, efficient to generate, and only requires a very small memory footprint in order to operate.

1.1 How to Read this Document

This section is non-normative.

This document is a detailed specification for a serialization of Linked Data in JSON. The document is primarily intended for the following audiences:

This specification does not describe the programming interfaces for the JSON-LD Syntax. The specification that describes the programming interfaces for JSON-LD documents is the JSON-LD Application Programming Interface [ JSON-LD-API ].

To understand the basics in this specification you must first be familiar with JSON, which is detailed in [ RFC4627 ].

JSON [ RFC4627

] defines several terms which are 1.2 General Terminology

The following is an explanation of the general terminology used throughout in this document:

JSON object
An object structure is represented as a pair of curly brackets surrounding zero or more name-value pairs. A name is a string . A single colon comes after each name, separating the name from the value. A single comma separates a value from a following name. The names within an object should be unique.
array
In JSON, an array is an ordered sequence of zero or more values. An array is represented as square brackets surrounding zero or more values that are separated by commas. 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 specific markup is provided (see 4.9 Sets and Lists ).
string
A string is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes (if necessary). A character is represented as a single character string.
number
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.
true and false
Values that are used to express one of two possible boolean states.
null
The null value is used to make the JSON-LD processor "forget" any previously defined JSON key that is associated with the null value. If a previous definition doesn't exist, the entire key-value is ignored. If a previous definition of the key does exist, the previous definition is undefined.
subject node definition
A JSON object used to represent a subject node and one or more properties of that subject. node. A JSON object is a subject node definition if it does not contain they keys @value , @list or @set and it has one or more keys other than @id . A node definition may be spread among different parts of a document or even between different documents.
subject node reference
A JSON object used to reference a subject node having only the @id key.

2. Design Goals and Rationale

This section is non-normative.

A number of design goals were established before the creation of this markup language:

Simplicity
No extra processors or software libraries should be necessary to use JSON-LD in its most basic form. The language will provide developers with a very easy learning curve. Developers need only know JSON and two keywords ( @context and @id ) to use the basic functionality in JSON-LD.
Compatibility
The JSON-LD markup must be 100% compatible with JSON. This ensures that all of the standard JSON libraries work seamlessly with JSON-LD documents.
Expressiveness
The syntax must be able to express directed graphs, which have been proven to be able to express almost every real world data model.
Terseness
The JSON-LD syntax must be very terse and human readable, requiring as little effort as possible from the developer.
Zero Edits, most of the time
JSON-LD must provide a mechanism that allows developers to specify context in a way that is out-of-band. This allows organizations that have already deployed large JSON-based infrastructure to add meaning to their JSON documents in a way that is not disruptive to their day-to-day operations and is transparent to their current customers. At times, mapping JSON to a graph representation can become difficult. In these instances, rather than having JSON-LD support an esoteric use case, we chose not to support the use case and support a simplified syntax instead. So, while Zero Edits is a design goal, it is not always possible without adding great complexity to the language.
One-pass Processing
JSON-LD supports one-pass processing, which results in a very small memory footprint when processing documents. For example, to expand a JSON-LD document from a compacted form, only one pass is required over the data.
Linked Data-centric
The focus on Linked Data is placed at a much higher priority than the focus on the Semantic Web. One outcome of this ordering of priorities is an aggressively reduced focus on the Semantic Web stack (RDF [ RDF-CONCEPTS ], TURTLE [ TURTLE-TR ], triple stores, and SPARQL [ RDF-SPARQL-QUERY ]). While this may be off-putting to proponents of the Semantic Web, the audience for this specification are Web developers that want a gentler introduction and a simpler technology stack for using Linked Data in their Web applications. Semantic Web concepts, such as conversion to and from RDF, are fully supported by JSON-LD, but the implementation of these features are not elaborated upon in this specification. See B. Relationship to Other Linked Data Formats and Data Models for more information about how JSON-LD integrates into the more traditional Semantic Web stack.

3. Basic Concepts

This section is normative.

JSON-LD is designed to ensure that Linked Data concepts can be marked up in a way that is simple to understand and create by Web authors. In many cases, regular JSON markup can become Linked Data with the simple addition of a context . As more JSON-LD features are used, more semantics are added to the JSON markup.

3.1 Linking Linked Data

The following definition for Linked Data is the one that will be used for this specification.

  1. Linked Data is a set of documents, each containing a representation of a linked data graph .
  2. A linked data graph is an unordered labeled directed graph, where nodes are subject IRIs or Blank Nodes , or other values.
  3. A node having an outgoing edge must be an IRI or Blank Node .
  4. A node having an incoming edge must be an IRI , Blank Node , or value such as a number or string.
  5. A node may have both incoming and outgoing edges.
  6. An edge must be labeled with an absolute IRI , within the JSON-LD syntax, this label is called a property .
  7. IRIs used within a linked data graph should be dereferenceable to a Linked Data document describing the resource denoted by that IRI .
Note

A Linked Data document does not necessarily need to be expressed in JSON-LD. The notion of Linked Data is a concept independent of any given serialization format. In particular, any document based on an RDF serialization format is a Linked Data document.

This definition of Linked Data is entirely consistent with that in [ RDF-CONCEPTS ], although Linked Data may not be a valid RDF document, any RDF document is an expression of Linked Data .

Issue

An illustration of a linked data graph would probably help here.

Richard Cyganiak suggests that the data model is at odds with [ RDF-CONCEPTS ] and should be more closely aligned with it instead of creating new terminology.

Note that this definition is provisional, and may be reverted to something closer to the original depending on community feedback.

  1. Linked Data is a set of documents, each containing a representation of a linked data graph .
  2. A linked data graph is an unordered labeled directed graph, where nodes are subject s or object s, and edges are labeled using properties .
  3. A subject is any node in a linked data graph with at least one outgoing edge.
  4. A subject should be labeled with an IRI (an Internationalized Resource Identifier as described in [ RFC3987 ]).
  5. An object is a node in a linked data graph with at least one incoming edge.
  6. An object may be labeled with an IRI or a label that is not an IRI such as plain text, internationalized text, or a strictly-typed data value.
  7. A node may be a subject and an object at the same time.
  8. A property is the label on an edge in a linked data graph .
  9. A property should be an IRI .
  10. An IRI that is a label in a linked data graph should be dereferencable to a Linked Data document describing the labeled subject , , property or object . .
Issue 1
An illustration of a linked data graph would probably help here. Issue 2 EricP suggests that the definitions of subject and object, while being practical, are at odds with [ RDF-CONCEPTS ] use in their roles within a triple.
Note

JSON-LD allows properties to be BNodes, while RDF does not. When used as just JSON-LD, this is not unreasonable; it only becomes an issue (and could raise an exception) when transformed to RDF.

Note that the definition for Linked Data above is silent on the topic of unlabeled nodes . Nevertheless, this specification allows for the expression of unlabeled nodes , as most graph-based data sets on the Web contain a number of associated nodes that are not named and thus are not directly de-referenceable.

JSON-LD defines a mechanism to map JSON terms, i.e., keys and values, to IRIs. This does not mean that JSON-LD requires every key or value to be an IRI , but rather ensures that keys and values can be mapped to IRIs if the developer desires to transform their data into Linked Data . There are a few techniques that can ensure that developers will generate good Linked Data for the Web. JSON-LD formalizes those techniques.

We will be using the following JSON markup as the example for the rest of this section:

{
Example 1: Sample JSON object
{
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "depiction": "http://twitter.com/account/profile_image/manusporny"
}

3.1.1 3.2 Syntax Tokens and Keywords

JSON-LD specifies a number of syntax tokens and keywords that are a core part of the language:

@context
Used to define the short-hand names that are used throughout a JSON-LD document. These short-hand names are called term s and help developers to express specific identifiers in a compact manner. The @context keyword is described in detail in the section titled 3.3 The Context .
@graph
Used to explicitly label a linked data graph . This keyword is described in the section titled 4.11 Named Graphs .
@id
Used to uniquely identify things that are being described in the document. This keyword is described in the section titled Identifying the Subject 3.6 Node Identifiers .
@value
Used to specify the data that is associated with a particular property in the graph. This keyword is described in the sections titled 3.8 String Internationalization and 4.2 Typed Values .
@language
Used to specify the native language for a particular value or the default language of a JSON-LD document. This keyword is described in the section titled 3.8 String Internationalization .
@type
Used to set the data type of a subject node or typed value . This keyword is described in the section titled 4.2 Typed Values .
@container
Used to set the container of a particular value. This keyword is described in the section titled 4.9 Sets and Lists .
@list
Used to express an ordered set of data. This keyword is described in the section titled 4.9 Sets and Lists .
@set
Used to express an unordered set of data. This keyword is described in the section titled 4.9 Sets and Lists .
@vocab
Used to set the base IRI for all property IRIs affected by the active context . This keyword is described in section 3.5 IRIs .
:
The separator for JSON keys and values that use compact IRIs .

For the avoidance of doubt, all keys, keywords , and values in JSON-LD are case-sensitive.

3.1.2 3.3 The Context

In JSON-LD, a context is used to map term s, i.e., properties with associated values in an JSON document, to IRI s. A term is a short word that expands to an IRI . Term s may be defined as any valid JSON string other than a JSON-LD keyword . To avoid forward-compatibility issues, term s starting with an @ character should not be used as they might be used as keywords in future versions of JSON-LD. Furthermore, the use of empty terms ( "" ) is discouraged as not all programming languages are able to handle empty property names.

The Web uses IRIs for unambiguous identification. The idea is that these term s mean something that may be of use to other developers and that it is useful to give them an unambiguous identifier. That is, it is useful for term s to expand to IRIs so that developers don't accidentally step on each other's vocabulary terms and other resources. Furthermore, developers, and machines, are able to use this IRI (by plugging it directly into a web browser, for instance) to go to the term and get a definition of what the term means. This mechanism is analogous to the way we can use WordNet today to see the definition of words in the English language. Developers and machines need the same sort of definition of terms. IRIs provide a way to ensure that these terms are unambiguous. For example, the term name may map directly to the IRI http://xmlns.com/foaf/0.1/name . This allows JSON-LD documents to be constructed using the common JSON practice of simple name/value pairs while ensuring that the data is useful outside of the page, API or database in which it resides. The value of a term mapping must be either; 1) a simple string with the lexical form of an absolute IRI or 2) compact IRI , or 3) an JSON object containing an @id , @type , @language , or @container keyword (all other keywords are ignored by a JSON-LD processor).

These Linked Data term s are typically collected in a context document that would look something like this:

{
Example 2: Context definition
{
  "@context":
  {
    "name": "http://xmlns.com/foaf/0.1/name",
    "depiction":
    {
      "@id": "http://xmlns.com/foaf/0.1/depiction",
      "@type": "@id"
    },
    "homepage":
    {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"
    },
  }
}

Assuming that this context document can be retrieved at http://json-ld.org/contexts/person.jsonld , it can be referenced from a JSON-LD document by adding a single line. The JSON markup shown in the previous section could be changed as follows:

{
Example 3: Adding context reference to JSON document
{
  "@context": "http://json-ld.org/contexts/person.jsonld",
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "depiction": "http://twitter.com/account/profile_image/manusporny"
}

The additions above transform the previous JSON document into a JSON document with added semantics because the @context specifies how the name , homepage , and depiction terms map to IRIs . Mapping those keys to IRIs gives the data global context. If two developers use the same IRI to describe a property, they are more than likely expressing the same concept. This allows both developers to re-use each others' data without having to agree to how their data will interoperate on a site-by-site basis. Contexts may also contain type information for certain term s as well as other processing instructions for the JSON-LD processor.

Note

External JSON-LD context documents may contain extra information located outside of the @context key, such as documentation about the terms declared in the document. When importing a @context value from an external JSON-LD context document, any extra information contained outside of the @context value must be discarded.

Contexts may be specified in-line. This ensures that JSON-LD documents can be processed when a JSON-LD processor does not have access to the Web.

{
Example 4: In-line context definition
{
  "@context":
  {
    "name": "http://xmlns.com/foaf/0.1/name",
    "depiction":
    {
      "@id": "http://xmlns.com/foaf/0.1/depiction",
      "@type": "@id"
    },
    "homepage":
    {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"
    },
  },
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "depiction": "http://twitter.com/account/profile_image/manusporny"
}

Contexts may be used at any time a subject node definition is defined. A subject node definition may specify multiple contexts, using an array , which is processed in order. This is useful when an author would like to use an existing context and add application-specific terms to the existing context. Duplicate context term s must be overridden using a last-defined-overrides mechanism.

Example 5: Scoped contexts within node definitions
{
  "@context":
  {
    "name": "http://example.com/person#name",
    "details": "http://example.com/person#details"
  },
  "name": "Markus Lanthaler",
  ...
  "details":
  {
    "@context": {
      "name": "http://example.com/organization#name"
    },
    "name": "Graz University of Technology"
  }
}

In the example above, the name prefix is overridden in the more deeply nested details structure. Note that this is rarely a good authoring practice and is typically used when there exist legacy applications that depend on the specific structure of the JSON object .

Note

If a term is re-defined within a context, all previous rules associated with the previous definition are removed. A term defined in a previous context must be removed, if it is re-defined to null .

The set of contexts defined within a specific subject node definition are referred to as local context s. Setting the context to null effectively sets resets the local active context to the initial context (further explained in the JSON-LD API, Appendix A, Initial Context [ JSON-LD-API ] ). an empty context. The active context refers to the accumulation of local context s that are in scope at a specific point within the document. The following example specifies an external context and then layers a local context on top of the external context:

{
Example 6: Combining external and local contexts
{
  "@context": [
    "http://json-ld.org/contexts/person.jsonld",
    {
      "pic": "http://xmlns.com/foaf/0.1/depiction"
    }
  ],
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "pic": "http://twitter.com/account/profile_image/manusporny"
}
Note

To ensure the best possible performance, it is a best practice to put the context definition at the top of the JSON-LD document. If it isn't listed first, processors have to save each key-value pair until the context is processed. This creates a memory and complexity burden for certain types of low-memory footprint JSON-LD processors.

Note

The null value is processed in a special way in JSON-LD. Unless otherwise specified, a JSON-LD processor must act as if a key-value pair in the body of a JSON-LD document was never declared when the value equals null . If @value , @list , or @set is set to null in expanded form, then the entire JSON object is ignored. If @context is set to null , the active context is reset and when used within a context , it removes any definition associated with the key, unless otherwise specified.

3.1.3 3.4 From JSON to JSON-LD

If a set of term s such as, name , homepage , and depiction , are defined in a context , and that context is used to resolve the names in JSON objects , machines are able to automatically expand the terms to something meaningful and unambiguous, like this:

{
Example 7: Expanded terms
{
  "http://xmlns.com/foaf/0.1/name": "Manu Sporny",
  "http://xmlns.com/foaf/0.1/homepage": "http://manu.sporny.org"
  "http://xmlns.com/foaf/0.1/depiction": "http://twitter.com/account/profile_image/manusporny"
}

Doing this allows JSON to be unambiguously machine-readable without requiring developers to drastically change their workflow.

Note

The example above does not use the @id keyword to set the subject of identify the node being described above. This type of node is called an unlabeled node . It is advised that all nodes described in JSON-LD are given unique identifiers via the @id keyword unless the data is not intended to be linked to from other data sets.

A JSON object used to define property values is called a subject node definition . Subject Node definitions do not require an @id . Subject Node definitions that do not contain an @id are known as an unlabeled nodes .

3.2 3.5 IRIs

IRI IRIs s are fundamental to Linked Data as that is how most subject nodes s, s and all properties and many object s are identified. IRI s can be expressed in a variety of different ways in JSON-LD.

An IRI (an Internationalized Resource Identifier) is described in [ RFC3987 ]) and the use with JSON-LD conforms to the definition of IRI in [ RDF-CONCEPTS ].

  1. Except within a context definition, term s in the key position in a JSON object that have a mapping to an absolute or a vocabulary base IRI or another term in the active context are expanded to an IRI by JSON-LD processors.
  2. An IRI is generated for the string value specified using @id or @type .
  3. An IRI is generated for the string value of any key for which there are coercion rules in effect that identify the value as an @id .

IRIs may be represented as an absolute IRI , a relative IRI , a term , or a compact IRI . , or as a value relative to @vocab .

An absolute IRI is defined in [ RFC3987 ] containing a scheme along with path and optional query and fragment segments. A relative IRI is an IRI that is relative to some other absolute IRI . In JSON-LD all relative IRI s are resolved relative to the base IRI associated with the document (typically, the directory that contains the document or the document itself).

IRIs can be expressed directly in the key position like so:

{
Example 8: IRI as a key
{
...
  "http://xmlns.com/foaf/0.1/name": "Manu Sporny",
...
}

In the example above, the key http://xmlns.com/foaf/0.1/name is interpreted as an IRI because it contains a colon ( : ) and the 'http' prefix does not exist in the context.

Term expansion occurs for IRIs if the value matches a term defined within the active context :

{
Example 9: Term expansion from context definition
{
  "@context":
  {
    "name": "http://xmlns.com/foaf/0.1/name"
...
  },
  "name": "Manu Sporny",
  "status": "trollin'",
...
}

Term s are case sensitive, and must be matched using a case-sensitive comparison.

JSON keys that do not expand to an absolute IRI are ignored, or removed in some cases, by the [ JSON-LD-API ]. However, JSON keys that do not include a mapping in the context are still considered valid expressions in JSON-LD documents - the keys just don't have any machine-readable, semantic meaning.

Prefix es are expanded when the form of the value is a compact IRI represented as a prefix:suffix combination, and the prefix matches a term defined within the active context :

{
Example 10: Prefix expansion
{
  "@context":
  {
    "foaf": "http://xmlns.com/foaf/0.1/"
...
  },
  "foaf:name": "Manu Sporny",
...
}

foaf:name above will automatically expand out to the IRI http://xmlns.com/foaf/0.1/name . See 4.1 Compact IRIs for more details.

If the @vocab is set, all keys that do not match a term or a prefix are It is often common that all types and properties come from the same vocabulary. JSON-LD's @vocab keyword allows to set a base IRI to be used for all properties and types that that do not match a term , a prefix , or an absolute IRI (i.e., do not contain a colon). The @vocab mapping must have a value of a simple string with the lexical form of an absolute IRI .

Example 11: Vocabulary base IRI
{  "@context": {
    "@vocab": "http://xmlns.com/foaf/1.0/"
  },
  "@type": "Person",
  "name": "Manu Sporny",
}

An IRI is generated when a JSON object is used in the value position that contains an @id keyword:

{
Example 12: Expanded IRI definition
{
...
  "homepage": { "@id": "http://manu.sporny.org" }
...
}
Note

Specifying a JSON object with an @id key is used to identify that object node using an IRI . When the object has only the @id , it is called a subject node reference . This facility may also be used to link to another subject node definition using a mechanism called embedding , which is covered in the section titled 4.10 Embedding .

If type coercion rules are specified in the @context for a particular term or property IRI , an IRI is generated:

Example 13: Type coercion
{
  "@context":
  {
    ...
    "homepage":
    {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"
    }
    ...
  }
...
  "homepage": "http://manu.sporny.org/",
...
}

In the example above, even though the value http://manu.sporny.org/ is expressed as a JSON string , the type coercion rules will transform the value into an IRI when processed by a JSON-LD Processor.

3.3 3.6 Identifying the Subject Node Identifiers

To be able to externally reference nodes in a graph, it is important that each node has an unambiguous identifier. IRI s are a fundamental concept of Linked Data , and nodes should have a de-referencable identifier used to name and locate them. For nodes to be truly linked, de-referencing the identifier should result in a representation of that node (for example, using a URL to retrieve a web page). Associating an IRI with a node tells an application that the returned document contains a description of the node requested.

JSON-LD documents may also contain descriptions of other nodes, so it is necessary to be able to uniquely identify each node which may be externally referenced.

A subject The node of a JSON object is a node identified using the @id key. The subject is the first piece of information needed by the JSON-LD processor in order to create the (subject, property, object) tuple, also known as a triple. keyword :

{
Example 14: Identifying a node
{
  "@context":
  {
    ...
    "homepage":
    {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"
    }
    ...
  },
  "@id": "http://example.org/people#joebob",
  "homepage": "http://manu.sporny.org/",
...
}

The example above would set the subject to contains a node identified by the IRI http://example.org/people#joebob .

A JSON object used to define property values is called a subject node definition . Subject Node definitions do not require an @id . A subject node definition that does not contain an @id property defines properties of an unlabeled node . Node definitions may be spread among different parts of a document or even between different documents.

Note

To ensure the best possible performance, when possible, it is a best practice to put JSON-LD keyword s, such as @id and @context before other key-value pairs in a JSON object . However, keys in a JSON object are not ordered, so processors must not depend on key ordering. If keywords are not listed first, processors have to save each key-value pair until at least the @context and the @id are processed. Not specifying those keywords first creates a memory and complexity burden for low-memory footprint processors, forcing them to use more memory and computing cycles than necessary.

3.4 3.7 Specifying the Type

The type of a particular subject node can be specified using the @type keyword . Specifying the type in this way will generate a triple of the form (subject, type, type- IRI ). To be considered Linked Data , types must be uniquely identified by an IRI .

{
Example 15: Specifying the type for a node
{
...
  "@id": "http://example.org/people#joebob",
  "@type": "http://xmlns.com/foaf/0.1/Person",
...
}

A node can be assigned more than one type by using the following markup pattern:

Example 16: Specifying multiple types for a node
{
...
  "@id": "http://example.org/places#BrewEats",
  "@type": ["http://schema.org/Restaurant", "http://schema.org/Brewery"]
...
}

3.5 3.8 String Internationalization

At times, it is important to annotate a string with its language. In JSON-LD this is possible in a variety of ways. Firstly, it is possible to define a default language for a JSON-LD document by setting the @language key in the @context or in a term definition:

{
Example 17: String Internationalization
{
  "@context":
  {
    ...
    "@language": "ja"
  },
  "name": "花澄",
  "occupation": "科学者"
}

The example above would associate the ja language code with the two string s 花澄 and 科学者 . Languages must be well-formed language tags according to [ BCP47 ].

It is possible to override the default language by using the expanded form of a value:

{
Example 18: Expanded value with language
{
  "@context": {
    ...
    "@language": "ja"
  },
  "name": "花澄",
  "occupation": {
    "@value": "Scientist",
    "@language": "en"
  }
}

It is also possible to override the default language or specify a plain value by omitting the @language tag or setting it to null when expressing the expanded value:

{
Example 19: Expanded value to remove language
{
  "@context": {
    ...
    "@language": "ja"
  },
  "name": {
    "@value": "Frank"
  },
  "occupation":  {
    "@value": "Ninja",
    "@language": "en"
  },
  "speciality": "手裏剣"
}
Note

Please note that language associations must only be applied to plain literal string s. That is, typed value s or values that are subject to type coercion 4.6 Type Coercion won't be language tagged.

To clear the default language for a subtree, @language can be set to null in a local context as follows:

{
Example 20: Clearing default language
{
  "@context": {
    ...
    "@language": "ja"
  },
  "name": "花澄",
  "details": {
    "@context": {
      "@language": null
    },
    "occupation": "Ninja"
  }
}
Note

JSON-LD allows one to associate language information with term s. See 4.5 Expanded Term Definition for more details.

3.6 3.9 JSON-LD Syntax

A JSON-LD document is first, and foremost, a JSON document (as defined in [ RFC5988 RFC4627 ]), and any syntactically correct JSON document must be processed by a conforming JSON-LD processor. However, JSON-LD describes a specific syntax to use for expressing Linked Data. This includes the use of specific keywords, as identified in 3.2 Syntax Tokens and Keywords for expressing subject node definitions , values, and the context . See Appendix A A. JSON-LD Grammar for authoring guidelines and a BNF description of JSON-LD.

4. Advanced Concepts

This section is normative.

JSON-LD has a number of features that provide functionality above and beyond the core functionality described above. The following section describes this advanced functionality in more detail.

4.1 Compact IRIs

Term s in Linked Data documents may draw from a number of different vocabularies . At times, declaring every single term that a document uses can require the developer to declare tens, if not hundreds of potential vocabulary term s that are used across an application. This is a concern for at least two reasons: the first is the cognitive load on the developer of remembering all of the term s, and the second is the serialized size of the context if it is specified inline. In order to address these issues, the concept of a compact IRI is introduced.

A compact IRI is a way of expressing an IRI using a prefix and suffix separated by a colon ( : ) which is similar to the CURIE Syntax in [ RDFA-CORE ]. The prefix is a term taken from the active context and is a short string identifying a particular IRI in a JSON-LD document. For example, the prefix foaf may be used as a short hand for the Friend-of-a-Friend vocabulary, which is identified using the IRI http://xmlns.com/foaf/0.1/ . A developer may append any of the FOAF vocabulary terms to the end of the prefix to specify a short-hand version of the absolute IRI for the vocabulary term. For example, foaf:name would be expanded out to the IRI http://xmlns.com/foaf/0.1/name . Instead of having to remember and type out the entire IRI , the developer can instead use the prefix in their JSON-LD markup.

Terms are interpreted as compact IRI s if they contain at least one colon and the first colon is not followed by two slashes ( // , as in http://example.com ). To generate the full IRI , the value is first split into a prefix and suffix at the first occurrence of a colon ( : ). If the active context contains a term mapping for prefix , an IRI is generated by prepending the mapped prefix to the (possibly empty) suffix using textual concatenation. If no prefix mapping is defined, the value is interpreted as an absolute IRI . If the prefix is an underscore ( _ ), the IRI remains unchanged. This effectively means that every term containing a colon will be interpreted by a JSON-LD processor as an IRI .

Consider the following example:

{
Example 21: Compact IRIs
{
  "@context":
  {
    "dc": "http://purl.org/dc/elements/1.1/",
    "ex": "http://example.org/vocab#"
  },
  "@id": "http://example.org/library",
  "@type": "ex:Library",
  "ex:contains":
  {
    "@id": "http://example.org/library/the-republic",
    "@type": "ex:Book",
    "dc:creator": "Plato",
    "dc:title": "The Republic",
    "ex:contains":
    {
      "@id": "http://example.org/library/the-republic#introduction",
      "@type": "ex:Chapter",
      "dc:description": "An introductory chapter on The Republic.",
      "dc:title": "The Introduction"
    }
  }
}

In this example, two different vocabularies are referred to using prefixes. Those prefixes are then used as type and property values using the compact IRI prefix:suffix notation.

It's also possible to use compact IRIs within the context as shown in the following example:

{
Example 22: Using vocabularies
{
  "@context":
  {
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "foaf": "http://xmlns.com/foaf/0.1/",
    "foaf:homepage": { "@type": "@id" },
    "picture": { "@id": "foaf:depiction", "@type": "@id" }
  },
  "@id": "http://me.markus-lanthaler.com/",
  "@type": "foaf:Person",
  "foaf:name": "Markus Lanthaler",
  "foaf:homepage": "http://www.markus-lanthaler.com/",
  "picture": "http://twitter.com/account/profile_image/markuslanthaler"
}

4.2 Typed Values

A value with an associated type, also known as a typed value , is indicated by associating a value with an IRI which indicates the value's type. Typed values may be expressed in JSON-LD in two three ways:

  1. By utilizing the @type keyword when defining a term within a @context section.
  2. By utilizing the expanded form for specifying objects. values.
  3. By using a native JSON type such as number , true , or false .

The first example uses the @type keyword to associate a type with a particular term in the @context :

{
Example 23: Expanded term definition with type coercion
{
  "@context":
  {
    "modified":
    {
      "@id": "http://purl.org/dc/terms/modified",
      "@type": "http://www.w3.org/2001/XMLSchema#dateTime"
    }
  },
...
  "modified": "2010-05-29T14:17:39+02:00",
...
}

The modified key's value above is automatically type coerced to a datetime value because of the information specified in the @context .

The second example uses the expanded form of setting the type information in the body of a JSON-LD document:

{
Example 24: Expanded value with type
{
  "@context":
  {
    "modified":
    {
      "@id": "http://purl.org/dc/terms/modified"
    }
  },
...
  "modified":
  {
    "@value": "2010-05-29T14:17:39+02:00",
    "@type": "http://www.w3.org/2001/XMLSchema#dateTime"
  }
...
}

Both examples above would generate an object with the value of 2010-05-29T14:17:39+02:00 and with the type of http://www.w3.org/2001/XMLSchema#dateTime . Note that it is also possible to use a term or a compact IRI to express the value of a type.

Note

The @type keyword is also used to associate a type with a subject node . Although the same keyword is used in both places, the The concept of an object node type and a value type are different. This is similar to object-oriented programming languages where both scalar and structured types use the same class inheritance mechanism, even though scalar types and structured types are inherently different.

Example 25: Example demonstrating the context-sensitivity for @type
{
...
  "@id": "http://example.org/posts#TripToWestVirginia",
  "@type": "http://schema.org/BlogPosting",
  "modified":
  {
    "@value": "2010-05-29T14:17:39+02:00",
    "@type": "http://www.w3.org/2001/XMLSchema#dateTime"
  }
...
}

The first use of @type associates a node type ( http://schema.org/BlogPosting ) with the node , which is expressed using the @id keyword . The second use of @type associates a value type ( http://www.w3.org/2001/XMLSchema#dateTime ) with the value expressed using the @value keyword . As a general rule, when @value and @type are used in the same JSON object , the @type keyword is expressing a value type . Otherwise, the @type keyword is expressing a node type .

4.3 External Contexts Language-tagged Strings

Authors may choose to declare JSON-LD context s in external documents to promote re-use of contexts as well as reduce the size of JSON-LD documents. In order to use an external context, A string with an author must specify associated language, also known as a language-tagged string , is indicated by associating a string with an IRI language code as defined in [ BCP47 to a valid ]. Language-tagged strings may be expressed in JSON-LD document. The referenced document must have in four ways:

  1. By defining a top-level subject definition . The value of any global language using the @context @language key keyword within that object is substituted for a @context section.
  2. By utilizing the IRI @language keyword when defining a term within a @context section.
  3. By utilizing the referencing document to have the same effect as if expanded form for specifying values.
  4. By utilizing the @container keyword with a value were specified inline of @language when defining a term within the referencing document. a @context section. This usage pattern is called a language map .

The following first example demonstrates uses the use of an external context: { , "name": "Manu Sporny", "homepage": "http://manu.sporny.org/", "depiction": "http://twitter.com/account/profile_image/manusporny" } Authors may also import multiple contexts or @language keyword to associate a combination of external and local contexts by specifying type with a list of contexts: particular term in the @context :

{
Example 26: Expanded term definition with language coercion
{
  "@context":
  [
    "http://json-ld.org/contexts/person.jsonld",
    {
      "foaf": "http://xmlns.com/foaf/0.1/"
    },
    "http://json-ld.org/contexts/event.jsonld"
  ],
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "foaf:depiction": "http://twitter.com/account/profile_image/manusporny",
  "celebrates":

  {
    "@type": "Event",
    "description": "International Talk Like a Pirate Day",
    "date": "R/2011-09-19"
  }

    "title":
    {
      "@id": "http://purl.org/dc/terms/title",
      "@language": "en"
    }
  },
...
  "title": "JSON-LD Syntax",
...

}

Each context in a list will be evaluated in-order. Duplicate mappings among the context s must be overwritten on a last-defined-overrides basis. The context list must modified contain either de-referenceable IRI s or JSON object s that conform key's value above is automatically language coerced to a English value because of the context syntax as described information specified in this document. the @context .

An author may nest contexts within subject definitions , with The second example uses the more deeply nested contexts overriding expanded form of setting the values language information in previously defined contexts: the body of a JSON-LD document:

{ "@context": { "name": "http://example.com/person#name", "details": "http://example.com/person#details" }, "": "Markus Lanthaler", ... "details":
Example 27: Expanded value with language
{
  "@context":

  {
    "@context": {
      "name": "http://example.com/organization#name"
    },
    "": "Graz University of Technology"
  }

    "title":
    {
      "@id": "http://purl.org/dc/terms/title"
    }
  },
...
  "title":
  {
    "@value": "JSON-LD Syntax",
    "@language": "en"
  }
...

}

In the example above, Both examples above would generate the value name JSON-LD Syntax prefix is overridden in tagged with the more deeply nested language details en structure. Note that this is rarely a good authoring practice and ; which is typically used when the JSON object has legacy applications using the structure of [ BCP47 ] code for the object. English language.

External JSON-LD context documents may contain extra information located outside of the @context key, Systems that support multiple languages often need to express data values in each language. Typically, such as documentation about systems also try to ensure that developers have a programatically easy way to navigate the prefixes datastructures for the language-specific data. In this case, language map declared s may be utilized.

Example 28: Language map expressing a property in three languages
{
  "@context":
  {
    "title":
    {
      "@id": "http://purl.org/dc/terms/title"
      "@container": "@language"
    }
  },
...
  "title":
  {
    "en": "JSON-LD Syntax",
    "ru": "JSON-LD Синтаксис",
    "ja": "JSON-LDの構文"
  }
...
}

In the example above, the title is expressed in three languages; English, Russian, and Japanese. To access the document. When importing data above in a @context value from an external JSON-LD context document, any extra information contained outside of programming language supporting dot-notation accessors for object properties, a developer may use the @context property.language value must be discarded. It is also recommended that a human-readable document is served as well pattern. For example, to explain access the correct usage Japanese version of the JSON-LD context document. title, a developer would use the following code snippet: obj.title.ja .

4.4 Referencing Contexts from JSON Documents

Ordinary JSON documents can be transformed into JSON-LD documents by referencing to an external JSON-LD context in an HTTP Link Header. Doing this allows JSON to be unambiguously machine-readable without requiring developers to drastically change their workflow and provides an upgrade path for existing infrastructure without breaking existing clients that rely on the application/json media type.

In order to use an external context with an ordinary JSON document, an author must specify an IRI to a valid JSON-LD document in an HTTP Link Header [ RFC5988 ] using the describedby link relation. The referenced document must have a top-level subject node definition . The @context subtree within that object is added to the top-level subject node definition of the referencing document. If an array is at the top-level of the referencing document and its items are subject node definitions , the @context subtree is added to all array items. All extra information located outside of the @context subtree in the referenced document must be discarded.

The following example demonstrates the use of an external context with an ordinary JSON document:

GET /ordinary-json-document.json HTTP/1.1
Example 29: Specifing context through HTTP header
GET /ordinary-json-document.json HTTP/1.1
Host: example.com
Accept: application/ld+json,application/json,*/*;q=0.1
====================================
HTTP/1.0 200 OK
...
Content-Type: application/json
Link: <http://json-ld.org/contexts/person.jsonld>; rel="describedby"; type="application/ld+json"
{
  "name": "Markus Lanthaler",
  "homepage": "http://www.markus-lanthaler.com/",
  "depiction": "http://twitter.com/account/profile_image/markuslanthaler"
}
Note

JSON-LD documents served with the application/ld+json media type must have all context information, including references to external contexts, within the body of the document.

4.5 Expanded Term Definition

Within a context definition, term s may be defined using an expanded notation to allow for additional information associated with the term to be specified (see also 4.6 Type Coercion and 4.9 Sets and Lists ).

Instead of using a string representation of an IRI , the IRI may be specified using a JSON object having an @id key. The value of the @id key must be either a term , a compact IRI , or an absolute IRI . Such an object is called a subject node reference .

{
Example 30: Expanded term definition
{
  "@context":
  {
    "foaf": { "@id": "http://xmlns.com/foaf/0.1/" },
    "name": { "@id": "http://xmlns.com/foaf/0.1/name" },
    "homepage": { "@id": "foaf:homepage" },
    "depiction": { "@id": "foaf:depiction" }
  },
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "depiction": "http://twitter.com/account/profile_image/manusporny"
}

This allows additional information to be associated with the term. This may be used for 4.6 Type Coercion , 4.9 Sets and Lists ), or to associate language information with a term as shown in the following example:

{
Example 31: Expanded term definition with language
{
  "@context": {
    ...
    "ex": "http://example.com/",
    "@language": "ja",
    "name": { "@id": "ex:name", "@language": null },
    "occupation": { "@id": "ex:occupation" },
    "occupation_en": { "@id": "ex:occupation", "@language": "en" },
    "occupation_cs": { "@id": "ex:occupation", "@language": "cs" }
  },
  "name": "Yagyū Muneyoshi",
  "occupation": "忍者",
  "occupation_en": "Ninja",
  "occupation_cs": "Nindža",
  ...
}

The example above would associate 忍者 with the specified default language code ja , Ninja with the language code en , and Nindža with the language code cs . The value of name , Yagyū Muneyoshi wouldn't be associated with any language code since @language was reset to null in the expanded term definition.

Expanded terms may also be defined using compact IRIs or absolute IRIs as keys. If the definition does not include an @id key, the expanded IRI is determined by performing expansion of the key within the current active context. This mechanism is mainly used to associate type or language information with a compact IRI or an absolute IRI .

Note

While it is possible to define a compact IRI , or an absolute IRI to expand to some other unrelated IRI (for example, foaf:name expanding to http://example.org/unrelated#species ), such usage is strongly discouraged.

4.6 Type Coercion

JSON-LD supports the coercion of values to particular data types. Type coercion allows someone deploying JSON-LD to coerce the incoming or outgoing values to the proper data type based on a mapping of data type IRI s to term s. Using type coercion, value representation is preserved without requiring the data type to be specified with each piece of data.

Type coercion is specified within an expanded term definition 4.5 Expanded Term Definition using the @type key. The value of this key represents a type IRI and must take the form of a term , compact IRI , absolute IRI , or the keyword @id . Specifying @id indicates that within the body of a JSON-LD document, a string value of a term coerced to @id is to be interpreted as an IRI .

Terms or compact IRIs used as the value of a @type key may be defined within the same context. This means that one may specify a term like xsd and then use xsd:integer within the same context definition - the JSON-LD processor will be able to determine the proper expansion for xsd:integer .

The example below demonstrates how a JSON-LD author can coerce values to typed value s, IRIs and lists.

{
Example 32: Expanded term definition with types
{
  "@context":
  {
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "http://xmlns.com/foaf/0.1/name",
    "age":
    {
      "@id": "http://xmlns.com/foaf/0.1/age",
      "@type": "xsd:integer"
    },
    "homepage":
    {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id",
      "@container": "@list"
    }
  },
  "name": "John Smith",
  "age": "41",
  "homepage":
  [
    "http://personal.example.org/",
    "http://work.example.com/jsmith/"
  ]
}

The example above would generate the following Turtle:

@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
Example 33
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
[ foaf:name "John Smith";
  foaf:age  "41"^^xsd:integer;
  foaf:homepage ( <http://personal.example.org/> <http://work.example.com/jsmith/> )
]
.

Terms may also be defined using absolute IRIs or compact IRIs . This allows coercion rules to be applied to keys which are not represented as a simple term . For example:

{
Example 34: Term definition with absolute IRI
{
  "@context":
  {
    "foaf": "http://xmlns.com/foaf/0.1/",
    "foaf:age":
    {
      "@type": "xsd:integer"
    },
    "foaf:homepage":
    {
      "@type": "@id"
    }
  },
  "foaf:name": "John Smith",
  "foaf:age": "41",
  "foaf:homepage":
  [
    "http://personal.example.org/",
    "http://work.example.com/jsmith/"
  ]
}

In this case the @id definition is optional, but if it does exist, the compact IRI or IRI is treated as a term (not a prefix:suffix construct) so that the actual definition of a prefix becomes unnecessary.

Note

Keys in the context are treated as terms for the purpose of expansion and value coercion. At times, this may result in multiple representations for the same expanded IRI . For example, one could specify that dog and cat both expanded to http://example.com/vocab#animal . Doing this could be useful for establishing different type coercion or language specification rules. It also allows a compact IRI (or even an absolute IRI ) to be defined as something else entirely. For example, one could specify that the term http://example.org/zoo should expand to http://example.org/river , but this usage is discouraged because it would lead to a great deal of confusion among developers attempting to understand the JSON-LD document.

Type coercion is performed using the unexpanded value of the key, which must have an exact match for an entry in the active context .

4.7 Property Generators

At times, an author may find that they need to express the same value for multiple properties. The simplest approach to accomplish this goal would be to do the following:

Example 35: Verbose expression of multiple properties with the same value
{
  "@context":
  {
    "title1": "http://purl.org/dc/terms/title",    "title2": "http://schema.org/name",    "title3": "http://www.w3.org/2000/01/rdf-schema#label"
  },
  "@id": "http://example.com/book",
  "title1": "The Count of Monte Cristo",  "title2": "The Count of Monte Cristo",  "title3": "The Count of Monte Cristo"
}

Unfortunately, the approach above produces redundant data and would become a publishing burden for large data sets. In these situations, the author may use a property generator to express a term once, but have the JSON-LD processor expand the single statement into multiple statements. This method can be accomplished by using the following markup pattern:

Example 36: Generating multiple properties using a single term
{
  "@context":
  {
    "title": { "@id": ["http://purl.org/dc/terms/title",
                       "http://schema.org/name",
                       "http://www.w3.org/2000/01/rdf-schema#label"] },
  },
  "@id": "http://example.com/book",
  "title": "The Count of Monte Cristo"
}

While the term above is only used once outside of the @context , a JSON-LD processor will internally transform the document above into the following set of statements:

Example 37
<http://example.com/book>
  <http://purl.org/dc/terms/title>
    "The Count of Monte Cristo" .
<http://example.com/book>
  <http://schema.org/name>
    "The Count of Monte Cristo" .
<http://example.com/book>
  <http://www.w3.org/2000/01/rdf-schema#label>
"The
Count
of
Monte
Cristo"
.

4.8 IRI Expansion Within a Context

In general, normal IRI expansion rules apply anywhere an IRI is expected (see 3.5 IRIs ). Within a context definition, this can mean that terms defined within the context may also be used within that context as long as there are no circular dependencies. For example, it is common to use the xsd namespace when defining typed value s:

{
Example 38: IRI expansion within context
{
  "@context":
  {
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "http://xmlns.com/foaf/0.1/name",
    "age":
    {
      "@id": "http://xmlns.com/foaf/0.1/age",
      "@type": "xsd:integer"
    },
    "homepage":
    {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"
    }
  },
  ...
}

In this example, the xsd term is defined and used as a prefix for the @type coercion of the age property.

Term s may also be used when defining the IRI of another term :

{
Example 39
{
  "@context":
  {
    "foaf": "http://xmlns.com/foaf/0.1/",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "foaf:name",
    "age":
    {
      "@id": "foaf:age",
      "@type": "xsd:integer"
    },
    "homepage":
    {
      "@id": "foaf:homepage",
      "@type": "@id"
    }
  },
  ...
}

Compact IRIs and IRIs may be used on the left-hand side of a term definition.

{
Example 40
{
  "@context":
  {
    "foaf": "http://xmlns.com/foaf/0.1/",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "foaf:name",
    "foaf:age":
    {
      "@type": "xsd:integer"
    },
    "foaf:homepage":
    {
      "@type": "@id"
    }
  },
  ...
}

In this example, the compact IRI form is used in two different ways. In the first approach, foaf:age declares both the IRI for the term (using short-form) as well as the @type associated with the term . In the second approach, only the @type associated with the term is specified. The JSON-LD processor will derive the full IRI for foaf:homepage by looking up the foaf prefix in the context .

Absolute IRIs may also be used in the key position in a context :

{
Example 41
{
  "@context":
  {
    "foaf": "http://xmlns.com/foaf/0.1/",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "foaf:name",
    "foaf:age":
    {
      "@id": "foaf:age",
      "@type": "xsd:integer"
    },
    "http://xmlns.com/foaf/0.1/homepage":
    {
      "@type": "@id"
    }
  },
  ...
}

In order for the absolute IRI to match above, the absolute IRI must also be used in the JSON-LD document. Also note that foaf:homepage will not use the { "@type": "@id" } declaration because foaf:homepage is not the same as http://xmlns.com/foaf/0.1/homepage . That is, a JSON-LD processor will use direct string comparison when looking up term s in a context before it applies the prefix lookup mechanism.

The only exception for using terms in the context is that they must not be used in a circular manner. That is, a definition of term-1 must not depend on the definition of term-2 if term-2 also depends on term-1 . For example, the following context definition is illegal:

{
Example 42
{
  "@context":
  {
    "term1": "term2:foo",
    "term2": "term1:bar"
  },
  ...
}

4.8 4.9 Sets and Lists

A JSON-LD author can express multiple values in a compact way by using array s. Since graphs do not describe ordering for links between nodes, arrays in JSON-LD do not provide an ordering of the listed objects contained elements by default. This is exactly the opposite from regular JSON arrays, which are ordered by default. For example, consider the following simple document:

{
Example 43
{
...
  "@id": "http://example.org/people#joebob",
  "nick": [ "joe", "bob", "jaybee" ],
...
}

The markup shown above would result in three triples being generated, each relating the subject node to an individual object , value, with no inherent order:

<http://example.org/people#joebob> <http://xmlns.com/foaf/0.1/nick> "joe" . <http://example.org/people#joebob> <http://xmlns.com/foaf/0.1/nick> "bob" .
Issue

Including an illustration might be better.

Example 44
<http://example.org/people#joebob> <http://xmlns.com/foaf/0.1/nick> "joe" .
<http://example.org/people#joebob> <http://xmlns.com/foaf/0.1/nick> "bob" .

<http://example.org/people#joebob>
   <http://xmlns.com/foaf/0.1/nick>

<http://xmlns.com/foaf/0.1/nick>

"jaybee"
.

Multiple values may also be expressed using the expanded form:

{
Example 45
{
  "@id": "http://example.org/articles/8",
  "dc:title": 
  [
    {
      "@value": "Das Kapital",
      "@language": "de"
    },
    {
      "@value": "Capital",
      "@language": "en"
    }
  ]
}

The markup shown above would generate the following triples, again with no inherent order:

<http://example.org/articles/8> <http://purl.org/dc/terms/title> "Das Kapital"@de .
Issue

Including an illustration might be better.

Example 46
<http://example.org/articles/8> <http://purl.org/dc/terms/title> "Das Kapital"@de .
<http://example.org/articles/8>
   <http://purl.org/dc/terms/title>

<http://purl.org/dc/terms/title>

"Capital"@en
.

As the notion of ordered collections is rather important in data modeling, it is useful to have specific language support. In JSON-LD, a list may be represented using the @list keyword as follows:

{
Example 47
{
...
  "@id": "http://example.org/people#joebob",
  "foaf:nick":
  {
    "@list": [ "joe", "bob", "jaybee" ]
  },
...
}

This describes the use of this array as being ordered, and order is maintained when processing a document. If every use of a given multi-valued property is a list, this may be abbreviated by setting @container to @list in the context :

{
Example 48
{
  "@context":
  {
    ...
    "nick":
    {
      "@id": "http://xmlns.com/foaf/0.1/nick",
      "@container": "@list"
    }
  },
...
  "@id": "http://example.org/people#joebob",
  "nick": [ "joe", "bob", "jaybee" ],
...
}
Note

List of lists are not allowed in this version of JSON-LD. If a list of lists is detected, a JSON-LD processor will throw an exception. This decision was made due to the extreme amount of added complexity when processing lists of lists.

Similarly to @list , there exists the keyword @set to describe unordered sets. While its use in the body of a JSON-LD document represents just syntactic sugar that must be optimized away when processing the document, it is very helpful when used within the context of a document. Values of terms associated with a @set or @list container are always represented in the form of an array - even if there is just a single value that would otherwise be optimized to a non-array form in a compacted document 4.15 Compact Document Form . This makes post-processing of the data easier as the data is always in array form, even if the array only contains a single value.

Note

The use of @container in the body of a JSON-LD document, i.e., outside @context must be ignored by JSON-LD processors.

4.9 4.10 Embedding

Object embedding Embedding is a JSON-LD feature that allows an author to use subject node definitions as property values. This is a commonly used mechanism for creating a parent-child relationship between two subject node s.

The example shows two subjects nodes related by a property from the first subject: node:

{
Example 49
{
...
  "name": "Manu Sporny",
  "knows":
  {
    "@type": "Person",
    "name": "Gregg Kellogg",
  }
...
}

A subject node definition , like the one used above, may be used in any value position in the body of a JSON-LD document.

4.10 4.11 Named Graphs

The @graph keyword is used to express a set of JSON-LD subject node definition s that may not be directly related to one another through a property. The mechanism may also be used where embedding is not desirable to the application. For example:

{
Example 50
{
  "@context": ...,
  "@graph":
  [
    {
      "@id": "http://manu.sporny.org/i/public",
      "@type": "foaf:Person",
      "name": "Manu Sporny",
      "knows": "http://greggkellogg.net/foaf#me"
    },
    {
      "@id": "http://greggkellogg.net/foaf#me",
      "@type": "foaf:Person",
      "name": "Gregg Kellogg",
      "knows": "http://manu.sporny.org/i/public"
    }
  ]
}

In this case, embedding doesn't work as each subject node definition references the other. Using the @graph keyword allows multiple resources to be defined within an array , and allows the use of a shared context . When used in a JSON object that is not otherwise a subject node definition , this describes resources in the default graph . This is equivalent to using multiple subject node definitions in array and defining the @context within each subject node definition :

Example 51
[
  {
    "@context": ...,
    "@id": "http://manu.sporny.org/i/public",
    "@type": "foaf:Person",
    "name": "Manu Sporny",
    "knows": "http://greggkellogg.net/foaf#me"
  },
  {
    "@context": ...,
    "@id": "http://greggkellogg.net/foaf#me",
    "@type": "foaf:Person",
    "name": "Gregg Kellogg",
    "knows": "http://manu.sporny.org/i/public"
  }

]

JSON-LD allows you to name things on the Web by assigning an @id to them, which is typically an IRI . This notion extends to the ability to identify graphs in the same manner. A developer may name data expressed using the @graph keyword by pairing it with an @id keyword . This enables the developer to make statements about a linked data graph itself, rather than just a single subject node .

{
Example 52
{
  "@context": ...,
  "@id": "http://example.org/graphs/73",
  "asOf": { "@value": "2012-04-09", "@type": "xsd:date" },
  "@graph":
  [
    {
      "@id": "http://manu.sporny.org/i/public",
      "@type": "foaf:Person",
      "name": "Manu Sporny",
      "knows": "http://greggkellogg.net/foaf#me"
    },
    {
      "@id": "http://greggkellogg.net/foaf#me",
      "@type": "foaf:Person",
      "name": "Gregg Kellogg",
      "knows": "http://manu.sporny.org/i/public"
    }
  ]
}

The example above expresses a named linked data graph that is identified by the IRI http://example.org/graphs/73 . That graph is composed of the statements about Manu and Gregg. Meta-data about the graph itself is also expressed via the asOf property, which specifies when the information was retrieved from the Web.

Issue 3

These examples could all have TriG definitions of their RDF results, but that would involve adding RDF earlier in the document.

4.11 4.12 Identifying Unlabeled Nodes

At times, it becomes necessary to be able to express information without being able to specify the subject. node. Typically, this type of node is called an unlabeled node or a blank node (see [ RDF-CONCEPTS ] Section 3.4: Blank Nodes ). In JSON-LD, unlabeled node identifiers are automatically created if a subject node is not specified using the @id keyword . However, authors may provide identifiers for unlabeled nodes by using the special _ (underscore) prefix . This allows one to reference the node locally within the document, but makes it impossible to reference the node from an external document. The unlabeled node identifier is scoped to the document in which it is used.

{
Example 53
{
...
  "@id": "_:foo",
...
}

The example above would set the subject node to _:foo , which can then be used elsewhere in the JSON-LD document to refer back to the unlabeled node . If a developer finds that they refer to the unlabeled node more than once, they should consider naming the node using a de-referenceable IRI so that it can be referenced also from other documents.

4.12 4.13 Aliasing Keywords

Each of the JSON-LD keywords , except for @context , may be aliased to application-specific keywords. This feature allows legacy JSON content to be utilized by JSON-LD by re-using JSON keys that already exist in legacy documents. This feature also allows developers to design domain-specific implementations using only the JSON-LD context .

{
Example 54
{
  "@context":
  {
     "url": "@id",
     "a": "@type",
     "name": "http://schema.org/name"
  },
  "url": "http://example.com/about#gregg",
  "a": "http://schema.org/Person",
  "name": "Gregg Kellogg"
}

In the example above, the @id and @type keywords have been given the aliases url and a , respectively.

4.13 4.14 Expanded Document Form

The JSON-LD API [ JSON-LD-API ] defines an method for expanding a JSON-LD document. Expansion is the process of taking a JSON-LD document and applying a @context such that all IRIs, types, and values are expanded so that the @context is no longer necessary.

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

{
Example 55
{
   "@context":
   {
      "name": "http://xmlns.com/foaf/0.1/name",
      "homepage": {
        "@id": "http://xmlns.com/foaf/0.1/homepage",
        "@type", "@id"

        "@type": "@id"

      }
   },
   "name": "Manu Sporny",
   "homepage": "http://manu.sporny.org/"
}

Running the JSON-LD Expansion algorithm against the JSON-LD input document provided above would result in the following output:

[
Example 56
[
  {
    "http://xmlns.com/foaf/0.1/name": [
      { "@value": "Manu Sporny" }
    ],
    "http://xmlns.com/foaf/0.1/homepage": [
      { "@id": "http://manu.sporny.org/" }
    ]
  }
]

Expanded document form is useful when an application has to process input data in a deterministic form. It has been optimized to ensure that the code that developers have to write is minimized compared to the code that would have to be written to operate on compact document form 4.15 Compact Document Form .

4.14 4.15 Compact Document Form

The JSON-LD API [ JSON-LD-API ] defines a method for compacting a JSON-LD document. Compaction is the process of taking a JSON-LD document and applying a context such that the most compact form of the document is generated. JSON is typically expressed in a very compact, key-value format. That is, full IRIs are rarely used as keys. At times, a JSON-LD document may be received that is not in its most compact form. JSON-LD, via the API, provides a way to compact a JSON-LD document.

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

[
Example 57
[
  {
    "http://xmlns.com/foaf/0.1/name": [ "Manu Sporny" ],
    "http://xmlns.com/foaf/0.1/homepage": [
      {
       "@id": "http://manu.sporny.org/"
      }
    ]
  }
]

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

{
Example 58
{
  "@context": {
    "name": "http://xmlns.com/foaf/0.1/name",
    "homepage": {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"
    }
  }
}

Running the JSON-LD Compaction algorithm given the context supplied above against the JSON-LD input document provided above would result in the following output:

{
Example 59
{
  "@context": {
    "name": "http://xmlns.com/foaf/0.1/name",
    "homepage": {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"
    }
  },
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/"
}

The compaction algorithm enables a developer to map any document into an application-specific compacted form by first expanding the document 4.14 Expanded Document Form . While the context provided above mapped http://xmlns.com/foaf/0.1/name to name , it could have also mapped it to any arbitrary string provided by the developer. This powerful mechanism, along with another JSON-LD API technique called framing , allows the developer to re-shape the incoming JSON data into a format that is optimized for their application.

A. JSON-LD Authoring Guidelines Grammar

Since the JSON-LD syntax This section is normative

This section is an attempt to formalize a subset of normative grammar for JSON-LD.

This appendix restates the JSON syntax, it follows that all valid syntactic conventions described in the previous sections more formally.

A JSON-LD processor should attempt to process non-conforming JSON-LD documents are valid JSON documents. It also means that an invalid JSON Conformance violations must be reported through a callback mechanism defined in [ JSON-LD-API ].

For a JSON-LD document can never to be conforming, it must be a valid JSON document as described in [ RFC4627 ].

JSON-LD document. Furthermore, JSON-LD places introduces a number of restrictions on keywords of the JSON syntax in order to define form ' @ ' followed by a set of authoring guidelines that are used to express well-formed one or more lower case alphabetic characters ( @[a-z]+ ). JSON-LD documents. At times, even if these guidelines are violated, documents should not define terms beginning with ' @ '. (See 3.2 Syntax Tokens and Keywords for a complete definition of JSON-LD processor will do its best to recover from the mistake and will deterministically transform the author's markup into well-formed JSON-LD. keywords).

Issue 4 Note

The final details of the guidelines are still being discussed ( ISSUE-114 JSON-LD context allows keywords ), as well as to be aliased within the best mechanism active context . Whenever a keyword is discussed, this is also understood to express these restrictions. EBNF doesn't quite capture what these guidelines are attempting apply to do - which is strongly express what constitutes a well-formed JSON-LD document. an alias for that keyword For example, if the time being, active context defines the term id as an alias for @id , that alias may be legitimately used as a simple list of plain English guidelines substitution for @id . Note that keyword aliases are provided. Issue 5 Per Andy S's comment , consider making this a normative syntax definition along with EBNF. not expanded during context processing.

A JSON-LD document is composed of either a a single subject node definition or an a JSON array containing a set of subject one or more node definitions . The value of @id must be a term ,

Example 60: Simple node definition
{
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "depiction": "http://twitter.com/account/profile_image/manusporny"
}
Example 61: Array of node definitions
[
  {
    "name": "Manu Sporny",
    "homepage": "http://manu.sporny.org/",
    "depiction": "http://twitter.com/account/profile_image/manusporny"
  }, {
    "name": "Gregg Kellogg",
    "homepage": "http://greggkellogg.net/",
    "depiction": "http://twitter.com/account/profile_image/gkellogg"
  }
]

A.1 Node Definition

A node definition is a compact JSON object containing one or more key/value pairs. Keys are IRI , or an s, compact IRI . s, term s defined within the active context , or one of the following keywords:

If the node definition contains the @context keyword key, it's value must be one of the following:

Example 62: Node definition with external context
{
  "@context": "http://json-ld.org/contexts/person.jsonld",
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "depiction": "http://twitter.com/account/profile_image/manusporny"
}

See 3.6 Node Identifiers , 4.1 Compact IRIs , and 4.12 Identifying Unlabeled Nodes for further discussion on @id values.

If the node definition contains the keys used in a @context @id key, it's value must be a null , an string having the lexical form of IRI , compact IRI (including unlabeled node ), or a JSON object . For each value that is a JSON object term that is associated with a key defined in a @context : the active context expanding into an @id and IRI or an unlabeled node .

Example 63: Node definition with @id
{
  "@context": "http://json-ld.org/contexts/person.jsonld",
  "@id": "http://manu.sporny.org/i/public",
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "depiction": "http://twitter.com/account/profile_image/manusporny"
}

If the node definition contains the @type key, it's value must be an either a string having the lexical form of absolute IRI , compact IRI , a term defined in the active context expanding into an absolute IRI , or null an array of any of these.

Note

A JSON-LD processor should process non-conforming documents having @container @type values including node definition or node reference entries but must be associated with a discard everything except for the value of either the @set @id or @list . key.

Example 64: Node definition with @type
{
  "@context": "http://json-ld.org/contexts/person.jsonld",
  "@id": "http://manu.sporny.org/i/public",
  "@type": "Person",
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "depiction": "http://twitter.com/account/profile_image/manusporny"
}

See 3.7 Specifying the Type for further discussion on @language @type values.

If the node definition contains the @graph key, it's value must be a string expressed in [ BCP47 node definition ] or an array of zero or more node definitions . If the node definition contains an null . Any @id keyword, its value is used as the label of a named graph.

Note

As a special case, if the JSON object contains no keys other property must than @graph and @context , and the JSON object is the root of the JSON-LD document, the JSON object is not treated as a node definition ; this is used as a way of defining node definitions that may not form a connected graph. This allows a context to be ignored defined which is shared by a all of the constituent node definitions .

Example 65: Multiple node definitions with a single context using @graph
{
  "@context": ...,
  "@graph":
  [
    {
      "@id": "http://manu.sporny.org/i/public",
      "@type": "foaf:Person",
      "name": "Manu Sporny",
      "knows": "http://greggkellogg.net/foaf#me"
    },
    {
      "@id": "http://greggkellogg.net/foaf#me",
      "@type": "foaf:Person",
      "name": "Gregg Kellogg",
      "knows": "http://manu.sporny.org/i/public"
    }
  ]
}

See 4.11 Named Graphs for further discussion on @graph values.

A JSON-LD processor and document must not contain any other keyword or alias expanding to any other keyword.

Other keys must expand to an absolute IRI using the active context . The values associated with these keys may be preserved in compaction and framing. any of the following:

A.2 Node Reference

A JSON object containing a only the @set @id key must (or alias) is a node reference and not have any other keys. a node definition .

Example 66: Explicit node reference
{
  "@context": ...,
  "@graph": [
    {
      "@id": "http://example.org/library",
      "@type": "ex:Library",
      "ex:contains": {"@id": "http://example.org/library/the-republic"}
    }, {
      "@id": "http://example.org/library/the-republic",
      "@type": "ex:Book",
      "dc:creator": "Plato",
      "dc:title": "The Republic",
      "ex:contains": {"@id": "http://example.org/library/the-republic#introduction"}
    }, {
      "@id": "http://example.org/library/the-republic#introduction",
      "@type": "ex:Chapter",
      "dc:description": "An introductory chapter on The Republic.",
      "dc:title": "The Introduction"
    }
  ]
}
}

A.3 Language Map

A JSON object language map containing may be used as a term value within a node definition if the term is defined with @list @container key set to @language .

The keys of a language map must not have be a [ BCP47 ] string with an associated value that is any other keys. of the following types:

We had also discussed values other than strings, such as those that might represent a more reified version of a value with other properties, such as is described using SKOS-XL .

Example 67: Language map expressing a property in three languages
{
  "@context":
  {
    "title":
    {
      "@id": "http://purl.org/dc/terms/title"
      "@container": "@language"
    }
  },
...
  "title":
  {
    "en": "JSON-LD Syntax",
    "ru": "JSON-LD Синтаксис",
    "ja": "JSON-LDの構文"
  }
...
}

A.4 Expanded Values

An expanded value is a JSON object that contains a containing the @value key: key, or an alias for the @value value key. It may have a also contain the @language @type or @type @language property and keys, or their respective keyword aliases. An expanded value must not have any contain keys other properties. It than @value , @language , and @type . An expanded value must not contain both the @language and @type keys at the same time. keys.

The value of the @value key key, or its alias, must be either a string , number , true , or false .

If an expanded value contains a number. @language key, it must not contain any other key except @value . The value of the @language key must be null or a string have the lexical form described in [ BCP47 ] format. ], or be null .

If an expanded value contains a @type key, it must not contain any other key except @value . The value of @type must be null , a term , a compact IRI , an absolute IRI , or null .

See 4.2 Typed Values and 4.3 Language-tagged Strings for a further discussion of expanded values .

A.5 List and Set Values

A list is a JSON object having only the @list keyword . Its value must be an array of any of the following:

A set is a JSON object having only the @set keyword . Its value must be an array containing a combination of any of the allowed values. following:

See 4.9 Sets and Lists for a further discussion of List and Set Values.

A.6 Context Definition

A context definition is a JSON object containing one or more key/value pairs. Keys are non-keyword strings or the body @language or @vocab keywords . A context definition should not contain any keys having the lexical form of keyword other than @language or @vocab .

If the context definition has a JSON-LD document, @language key, the value must have the lexical form described in [ BCP47 ] or be null .

If the context definition has a @vocab key, the value must have the lexical form of absolute IRI or be null .

Other keys are term definitions. Their values must be either a string , or a JSON object having the form of an expanded term definition (see 4.5 Expanded Term Definition ).

An expanded term definition is composed of zero or more keys from @id , @type , @language or @container . An expanded term definition must not be contain any other keys. All values associated with @id . This must expand to an absolute IRI .

If the term definition is not a compact IRI or absolute IRI , the expanded term definition must include the @id key.

If the expanded term definition contains the @id keyword , it must be a string having the lexical form of IRI , compact IRI , a term defined in contrast to the use defining context definition or the active context , or an array composed of any of the previous allowed values.

If the expanded term definition contains the @type keyword , it must be a string having the lexical form of absolute IRI , compact IRI , or a term defined in the defining context definition or the active context .

If the expanded term definition contains the @context @language keyword , the value must have the lexical form described in [ BCP47 ] or be null .

If the expanded term definition contains the @container keyword , the value must be either @list , where this @set , @language , or be null . If the value is allowed. @language , when the term is used outside of the @context , the associated value must be a JSON object whose keys are string s that are [ BCP47 ] language identifiers. The values associated with each [ BCP47 ] language string must be a string or an array of string s.

See 3.3 The Context and 4.5 Expanded Term Definition for a further discussion of contexts.

Example 68: Context definition with simple terms, expanded term definitions and @language
{
  "@language": "en",
  "xsd": "http://www.w3.org/2001/XMLSchema#",
  "foaf": "http://xmlns.com/foaf/0.1/",
  "name": "foaf:name",
  "depiction": {"@id": "foaf:depiction", "@type": "@id"},
  "modified": {"@id": "http://purl.org/dc/terms/modified", "@type": "xsd:dateTime"},
  "homepage": {"@id": "foaf:homepage", "@type": "@id", "@container": "@list"}
}

B. Relationship to other RDF Other Linked Data Formats and Data Models

This section is non-normative.

Issue 6

The intent of the Working Group and the Editors of this specification is to eventually align terminology used in this document with the terminology used in the RDF Concepts document [ RDF-CONCEPTS ] to the extent to which it makes sense to do so. In general, if there is an analogue to terminology used in this document in the RDF Concepts document, the preference is to use the terminology in the RDF Concepts document.

JSON-LD is a specification for representing Linked Data in JSON. A common way of working with Linked Data is through RDF , the Resource Description Framework. RDF can be expressed using JSON-LD by associating JSON-LD concepts such as @id and @type with the equivalent IRI s in RDF. Further information about RDF may be found in the [ RDF-PRIMER ].

The JSON-LD markup examples below demonstrate how JSON-LD can be used to express semantic data marked up in other languages and data models such as RDF, Turtle, RDFa, Microformats, and Microdata. These sections are merely provided as evidence that JSON-LD is very flexible in what it can express across different Linked Data approaches. Further information on transforming JSON-LD into RDF are detailed in the [ JSON-LD-API ].

B.1 RDF

This section is non-normative.

The RDF data model, as outlined in [ RDF-CONCEPTS ], is an abstract syntax for representing a directed graph of information. JSON-LD is capable of serializing any RDF graph, and performing full RDF to JSON-LD to RDF round-tripping. A complete description of how JSON-LD maps to RDF and algorithms detailing how one can convert from RDF to JSON-LD and from JSON-LD to RDF are included in the JSON-LD API [ JSON-LD-API ] specification.

B.2 Turtle

The following are examples of converting RDF expressed in [ TURTLE-TR ] into JSON-LD.

B.2.1 Prefix definitions

This section is non-normative.

The JSON-LD context has direct equivalents for the Turtle @prefix declaration:

@prefix foaf: <http://xmlns.com/foaf/0.1/> .
Example 69
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
<http://manu.sporny.org/i/public> a foaf:Person;
  foaf:name "Manu Sporny";
foaf:homepage
<http://manu.sporny.org/>
.
{
Example 70
{
  "@context":
  {
    "foaf": "http://xmlns.com/foaf/0.1/"
  },
  "@id": "http://manu.sporny.org/i/public",
  "@type": "foaf:Person",
  "foaf:name": "Manu Sporny",
  "foaf:homepage": { "@id": "http://manu.sporny.org/" }
}
Note

JSON-LD has no equivalent for the Turtle @base declaration. Instead, authors may use a prefix definition to resolve relative IRI s:

{ "@context": { "foaf": "http://xmlns.com/foaf/0.1/" }, "@id": , "@type": "foaf:Person", "foaf:name": "Manu Sporny", "foaf:homepage": { "@id": } }

B.2.2 Embedding

Both Turtle and JSON-LD allow embedding of objects, embedding, although Turtle only allows embedding of objects which use unlabeled node identifiers. nodes .

@prefix foaf: <http://xmlns.com/foaf/0.1/> .
Example 71
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
<http://manu.sporny.org/i/public>
  a foaf:Person;
  foaf:name "Manu Sporny";
foaf:knows
[
a
foaf:Person;
foaf:name
"Gregg
Kellogg"
]
.
{
Example 72
{
  "@context":
  {
    "foaf": "http://xmlns.com/foaf/0.1/"
  },
  "@id": "http://manu.sporny.org/i/public",
  "@type": "foaf:Person",
  "foaf:name": "Manu Sporny",
  "foaf:knows":
  {
    "@type": "foaf:Person",
    "foaf:name": "Gregg Kellogg"
  }
}

B.2.3 Lists

Both JSON-LD and Turtle can represent sequential lists of values.

@prefix foaf: <http://xmlns.com/foaf/0.1/> .
Example 73
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
<http://example.org/people#joebob> a foaf:Person;
  foaf:name "Joe Bob";
foaf:nick
(
"joe"
"bob"
"jaybee"
)
.
{
Example 74
{
  "@context":
  {
    "foaf": "http://xmlns.com/foaf/0.1/"
  },
  "@id": "http://example.org/people#joebob",
  "@type": "foaf:Person",
  "foaf:name": "Joe Bob",
  "foaf:nick":
  {
    "@list": [ "joe", "bob", "jaybee" ]
  }
}

B.3 RDFa

The following example describes three people with their respective names and homepages.

>
Example 75
<div prefix="foaf: http://xmlns.com/foaf/0.1/">
   <ul>
      <li typeof="foaf:Person">
        <a rel="foaf:homepage" href="http://example.com/bob/" property="foaf:name" >Bob</a>
      </li>
      <li typeof="foaf:Person">
        <a rel="foaf:homepage" href="http://example.com/eve/" property="foaf:name" >Eve</a>
      </li>
      <li typeof="foaf:Person">
        <a rel="foaf:homepage" href="http://example.com/manu/" property="foaf:name" >Manu</a>
      </li>
   </ul>
</div>

An example JSON-LD implementation using a single context is described below.

{
Example 76
{
  "@context":
  {
    "foaf": "http://xmlns.com/foaf/0.1/"
  },
  "@graph":
  [
    {
      "@type": "foaf:Person",
      "foaf:homepage": "http://example.com/bob/",
      "foaf:name": "Bob"
    },
    {
      "@type": "foaf:Person",
      "foaf:homepage": "http://example.com/eve/",
      "foaf:name": "Eve"
    },
    {
      "@type": "foaf:Person",
      "foaf:homepage": "http://example.com/manu/",
      "foaf:name": "Manu"
    }
  ]
}

B.4 Microformats

The following example uses a simple Microformats hCard example to express how the Microformat is represented in JSON-LD.

<div class="vcard">
Example 77
<div class="vcard">
 <a class="url fn" href="http://tantek.com/">Tantek Çelik</a>
</div>

The representation of the hCard expresses the Microformat terms in the context and uses them directly for the url and fn properties. Also note that the Microformat to JSON-LD processor has generated the proper URL type for http://tantek.com/ .

{
Example 78
{
  "@context":
  {
    "vcard": "http://microformats.org/profile/hcard#vcard",
    "url":
    {
      "@id": "http://microformats.org/profile/hcard#url",
      "@type": "@id"
    },
    "fn": "http://microformats.org/profile/hcard#fn"
  },
  "@type": "vcard",
  "url": "http://tantek.com/",
  "fn": "Tantek Çelik"
}

B.5 Microdata

The microdata example below expresses book information as a microdata Work item.

<dl itemscope
Example 79
<dl itemscope
    itemtype="http://purl.org/vocab/frbr/core#Work"
    itemid="http://purl.oreilly.com/works/45U8QJGZSQKDH8N">
 <dt>Title</dt>
 <dd><cite itemprop="http://purl.org/dc/terms/title">Just a Geek</cite></dd>
 <dt>By</dt>
 <dd><span itemprop="http://purl.org/dc/terms/creator">Wil Wheaton</span></dd>
 <dt>Format</dt>
 <dd itemprop="http://purl.org/vocab/frbr/core#realization"
     itemscope
     itemtype="http://purl.org/vocab/frbr/core#Expression"
     itemid="http://purl.oreilly.com/products/9780596007683.BOOK">
  <link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/BOOK">
  Print
 </dd>
 <dd itemprop="http://purl.org/vocab/frbr/core#realization"
     itemscope
     itemtype="http://purl.org/vocab/frbr/core#Expression"
     itemid="http://purl.oreilly.com/products/9780596802189.EBOOK">
  <link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/EBOOK">
  Ebook
 </dd>
</dl>

Note that the JSON-LD representation of the Microdata information stays true to the desires of the Microdata community to avoid contexts and instead refer to items by their full IRI .

[
Example 80
[
  {
    "@id": "http://purl.oreilly.com/works/45U8QJGZSQKDH8N",
    "@type": "http://purl.org/vocab/frbr/core#Work",
    "http://purl.org/dc/terms/title": "Just a Geek",
    "http://purl.org/dc/terms/creator": "Whil Wheaton",
    "http://purl.org/vocab/frbr/core#realization":
    [
      "http://purl.oreilly.com/products/9780596007683.BOOK",
      "http://purl.oreilly.com/products/9780596802189.EBOOK"
    ]
  },
  {
    "@id": "http://purl.oreilly.com/products/9780596007683.BOOK",
    "@type": "http://purl.org/vocab/frbr/core#Expression",
    "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/BOOK"
  },
  {
    "@id": "http://purl.oreilly.com/products/9780596802189.EBOOK",
    "@type": "http://purl.org/vocab/frbr/core#Expression",
    "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/EBOOK"
  }
]

C. IANA Considerations

This section is non-normative.

This section is included merely for standards community review and will be submitted to the Internet Engineering Steering Group if this specification becomes a W3C Recommendation.

application/ld+json

Type name:
application
Subtype name:
ld+json
Required parameters:
None
Optional parameters:
form
Determines the serialization form for the JSON-LD document. The only valid value at the moment is expanded . If no form is specified in an HTTP request header to an HTTP server, the server may choose any form. If no form is specified in an HTTP response, the form must not be assumed to take any particular form.
Encoding considerations:
The same as the application/json MIME media type.
Security considerations:
Since JSON-LD is intended to be a pure data exchange format for directed graphs, the serialization should not be passed through a code execution mechanism such as JavaScript's eval() function. It is recommended that a conforming parser does not attempt to directly evaluate the JSON-LD serialization and instead purely parse the input into a language-native data structure.
Interoperability considerations:
Not Applicable
Published specification:
The JSON-LD specification.
Applications that use this media type:
Any programming environment that requires the exchange of directed graphs. Implementations of JSON-LD have been created for JavaScript, Python, Ruby, PHP and C++.
Additional information:
Magic number(s):
Not Applicable
File extension(s):
.jsonld
Macintosh file type code(s):
TEXT
Person & email address to contact for further information:
Manu Sporny <msporny@digitalbazaar.com>
Intended usage:
Common
Restrictions on usage:
None
Author(s):
Manu Sporny, Gregg Kellogg, Markus Lanthaler, Dave Longley
Change controller:
W3C

Fragment identifiers used with application/ld+json resources may identify a node in the linked data graph expressed in the resource. This idiom, which is also used in RDF [ RDF-CONCEPTS ], gives a simple way to "mint" new, document-local IRIs to label nodes and therefore contributes considerably to the expressive power of JSON-LD.

D. 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, 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, RDFj. The work of Dave Lehn and Mike Johnson who reviewed, provided feedback, are appreciated for reviewing, and performed performing several implementations of the specification, and specification. Ian Davis, who created Davis is thanked for this work on RDF/JSON. Thanks also to Nath 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.

E. References

E.1 Normative references

[BCP47]
A. Phillips; M. Davis. Tags for Identifying Languages September 2009. IETF Best Current Practice. URL: http://tools.ietf.org/html/bcp47
[RDF-CONCEPTS]
RDF 1.1 Concepts and Abstract Syntax Richard Cyganiak, David Wood, Editors. World Wide Web Consortium (work in progress). 30 May 2012. Editor's Draft. This edition of the JSON-LD Syntax specification is http://www.w3.org/TR/2011/WD-rdf11-concepts-20110830/. The latest edition of the JSON-LD Syntax is available at http://www.w3.org/TR/rdf11-concepts/
[RFC3987]
M. Dürst; M. Suignard. Internationalized Resource Identifiers (IRIs). January 2005. Internet RFC 3987. URL: http://www.ietf.org/rfc/rfc3987.txt
[RFC4627]
D. Crockford. The application/json Media Type for JavaScript Object Notation (JSON) July 2006. Internet RFC 4627. URL: http://www.ietf.org/rfc/rfc4627.txt
[RFC5988]
Web Linking M. Nottingham. Editor. October 2010. IETF Standard. URL: http://tools.ietf.org/rfc/rfc5988.txt

E.2 Informative references

[JSON-LD-API]
The JSON-LD API 1.0 Manu Sporny, Gregg Kellogg, Dave Longley, Markus Lanthaler, Editors. World Wide Web Consortium (work in progress). 24 May 2012. Editor's Draft. This edition of the JSON-LD Syntax specification is http://json-ld.org/spec/ED/json-ld-api/20120524/. The latest edition of the JSON-LD Syntax is available at http://json-ld.org/spec/latest/json-ld-api/
[RDF-PRIMER]
Frank Manola; Eric Miller. RDF Primer. 10 February 2004. W3C Recommendation. URL: http://www.w3.org/TR/2004/REC-rdf-primer-20040210/
[RDF-SPARQL-QUERY]
Andy Seaborne; Eric Prud'hommeaux. SPARQL Query Language for RDF. 15 January 2008. W3C Recommendation. URL: http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115
[RDFA-CORE]
Shane McCarron; et al.