JSON-LD Framing allows developers to query by example and force a specific tree layout to a JSON-LD document.
This document is an experimental work in progress.
A JSON-LD document is a representation of a directed graph. A single directed graph can have many different serializations, each expressing exactly the same information. Developers typically work with trees, represented as JSON objects. While mapping a graph to a tree can be done, the layout of the end result must be specified in advance. A Frame can be used by a developer on a JSON-LD document to specify a deterministic layout for a graph.
This document is a detailed specification for a serialization of Linked Data in JSON. The document is primarily intended for the following audiences:
There are a number of ways that one may participate in the development of this specification:
There is one class of products that can claim conformance to this specification: JSON-LD Processors.
A conforming JSON-LD Processor is a system which can perform the Framing operation in a manner consistent with the algorithms defined in this specification.
JSON-LD Processors MUST NOT attempt to correct malformed IRIs or language tags; however, they MAY issue validation warnings. IRIs are not modified other than conversion between relative and absolute IRIs.
The algorithms in this specification are generally written with more concern for clarity than efficiency. Thus, JSON-LD Processors MAY implement the algorithms given in this specification in any way desired, so long as the end result is indistinguishable from the result that would be obtained by the specification's algorithms.
Implementers can partially check their level of conformance to this specification by successfully passing the test cases of the JSON-LD test suite [[JSON-LD-TESTS]]. Note, however, that passing all the tests in the test suite does not imply complete conformance to this specification. It only implies that the implementation conforms to aspects tested by the test suite.
All algorithms described in this section are intended to operate on language-native data structures. That is, the serialization to a text-based JSON document isn't required as input or output to any of these algorithms.
Reference to JSON data structures are interpreted using their abstract representation for the purpose of describing algorithms.
This specification adds a number of keywords to the ones defined in the [[!JSON-LD]] specification:
@embedas the following:
@embednor object embed flag is not specified.
nullshould be returned, which would otherwise be removed when Compacting.
All JSON-LD tokens and keywords are case-sensitive.
Framing is the process of taking a JSON-LD document, which expresses a graph of information, and applying a specific graph layout (called a Frame).
Framing makes use of the Node Map Generation algorithm to place each object defined in the JSON-LD document into a map of flattened subjects, allowing them to be operated upon by the Framing algorithm.
A valid JSON-LD Frame is a superset of a valid JSON-LD document, allowing additional content, which is preserved through expansion. The Grammar defined in [[JSON-LD]] is extended as follows:
Additionally, values of the
@embed key MUST only be one of
the following keyword values, or an array containing only one of
Otherwise, an invalid @embed value error has been detected and processing is aborted.
@defaultMAY include the value
@null, or an array containing only
@null, in addition to other values allowed in the grammar for values of keys expanding to absolute IRIs. Processors MUST preserve this value when expanding. All other key/value pairs of a default object MUST be ignored.
@typemay also be an empty JSON object, or an array containing only an empty JSON object. Processors MUST preserve this value when expanding.
The framing algorithm takes an JSON-LD input (expanded input), which MUST be a JSON-LD document in expanded form, an input frame (expanded frame), which MUST be a JSON-LD frame in expanded form, a context (context), and a number of options and produces JSON-LD output.
If an error is detected in the expanded frame, a processor MUST generate a JsonLdFramingError with code set to invalid frame. Need more specifics as to what constitutes a valid frame.
The recursive algorithm operates with a framing state (state),
created initially using
the object embed flag set to
the explicit inclusion flag set to
the require all flag set to
and the omit default flag set to
along with map of flattened subjects
set to the
@merged property of the result of performing the
Node Map Generation algorithm on
subjectStack set to an empty array,
link set to an empty dictionary.
Also initialize results as an empty array.
Processors MAY use other runtime options to set different framing state defaults for values of state.
Invoke the recursive algorithm using framing state (state),
the keys from the map of flattened subjects as subjects,
expanded frame (frame), result as parent, and
null as active property.
The recursive algorithm adds elements to parent either by appending
the element to parent, if it is an array, or by appending it
to an array associated with active property in parent, if it is a dictionary.
Note that if parent is an array, active property MUST be
and if it is a dictionary, it MUST NOT be
The following series of steps is the recursive portion of the framing algorithm:
@typeproperty including any IRI from the corresponding
@typeproperty in frame.
@typeproperty and frame has a
@typeproperty containing only an empty dictionary.
falseand both node and frame contain common non-keyword properties of any value. Having any value might not be adequate, as contained nodes might have other matching criteria that could fail to match.
trueand all the non-keyword properties in frame exist in node with any value, or properties missing in node each have a property in frame which has a dictionary value containing only the key
@defaultwith any value.
Can we remove sorting, or make it subject to a processing flag? In general, sorting is a performance problem for JSON-LD, and inhibits stream processing.
@idand id and add output to link associated with id.
@linkand id is in link, node already exists in results. Add the associated node object from link to parent and do not perform additional processing for this node.
@neveror if a circular reference would be created by an embed, add output to parent and do not perform additional processing for this node.
@last, remove any existing embedded node from parent. Requires sorting of subjects. We could consider
@sample, to embed just the first matched node. With sorting, we could also consider
true, processors MUST NOT add any values for property to output, and the following steps are skipped.
@list, then each listitem in the list is processed in sequence and added to a new list dictionary in output:
@idfrom listitem as the sole member of a new subjects array, the first value from
@listin frame as frame, list as parent, and
@listas active property. Could this use the list array, and
nullfor active property?
@idfrom item as the sole member of a new subjects array, the first value from property in frame as frame, output as parent, and property as active property.
@omitDefaultwith a value of
true, or does not contain
@omitDefaultand the value of the omit default flag is
@preserveand a value that is a copy of the value of
@defaultin frame if it exists, or the string
@reverse, then for each reverse property and sub frame that are the values of
@reverseproperty in output with a new dictionary reverse dict as its value.
nullas active property, and the array value of reverse property in reverse dict as parent.
Using result from the recursive algorithm, set compacted results to the result of using the
method using results, context, and
If compacted results does not have a top-level
@graph keyword, or if its value is
not an array, modify compacted results to place the non
of compacted results into a dictionary contained within the array value of
Recursively, replace all key-value pairs in compacted results
where the key is
@preserve with the value from the key-pair.
If the value from the key-pair is
@null, replace the value with
If, after replacement, an array contains only the value null remove the value, leaving
an empty array.
Return compacted results.
To support the specifics of framing, the Expansion Algorithm is extended to support free-floating nodes. A free-floating node is a node reference which is not used as an object.
When run in the json-ld-framing-1.1-expand-frame processing mode, the algorithm is modified as follows:
@requireAll), set expanded value to the result of performing the Expansion Algorithm recursively, passing active context, active property, and value for element.
This API provides a clean mechanism that enables developers to convert JSON-LD data into a a variety of output formats that are easier to work with in various programming languages. If a JSON-LD API is provided in a programming environment, the entirety of the following API MUST be implemented.
The JSON-LD Processor interface is the high-level programming structure that developers use to access the JSON-LD transformation methods. The definition below is an experimental extension of the interface defined in the [[JSON-LD-API]].
The JsonLdProcessor interface
input using frame
according to the steps in the Framing
expandmethod using frame and options with
processingModeset to "json-ld-framing-1.1-expand-frame".
@contextfrom frame, if it exists, or to a new empty context, otherwise.
input; either in the form of an JSON object or as IRI.
JSON-LD Framing extends the error interface and codes defined in [[JSON-LD-API]].
@embedis not one recognized for the object embed flag.
This section describes datatype definitions used within the JSON-LD API.
The JsonLdContext type is used to refer to a value that that may be a JSON object, a string representing an IRI, or an array of JSON objects and strings.
See JsonLdOptions definition in [[!JSON-LD-API]].
The JsonLdOptions type is used to convert a set of options to an interface method.
See JsonLdOptions definition in [[!JSON-LD-API]].
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/jsonMIME media type.
eval()function. It is RECOMMENDED that a conforming parser does not attempt to directly evaluate the JSON-LD frame and instead purely parse the input into a language-native data structure.
Fragment identifiers have no meaning with application/frame-ld+json resources.
The following is a list of open issues being worked on for the next release.
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. The work of Dave Lehn and Mike Johnson are appreciated for reviewing, and performing several implementations of the specification. Ian Davis is thanked for this work on RDF/JSON. Thanks also to Nathan Rixham, Bradley P. Allen, Kingsley Idehen, Glenn McDonald, Alexandre Passant, Danny Ayers, Ted Thibodeau Jr., Olivier Grisel, Josh Mandel, Eric Prud'hommeaux, David Wood, Guus Schreiber, Pat Hayes, Sandro Hawke, and Richard Cyganiak for their input on the specification.