JSON-LD 1.1 (original) (raw)
Abstract
JSON is a useful data serialization and messaging format. This specification defines JSON-LD 1.1, a JSON-based format to serialize Linked Data. The syntax is designed to easily integrate into deployed systems that already use JSON, and provides a smooth upgrade path from JSON to JSON-LD. It is primarily intended to be a way to use Linked Data in Web-based programming environments, to build interoperable Web services, and to store Linked Data in JSON-based storage engines.
This specification describes a superset of the features defined inJSON-LD 1.0 [JSON-LD10] and, except where noted, documents created using the 1.0 version of this specification remain compatible with JSON-LD 1.1.
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 theW3C technical reports index at https://www.w3.org/TR/.
This document has been developed by theJSON-LD Working Group and was derived from the JSON-LD Community Group's Final Report.
There is alive JSON-LD playground that is capable of demonstrating the features described in this document.
This specification is intended to supersede the JSON-LD 1.0 [JSON-LD10] specification.
This document was published by the JSON-LD Working Group as a Recommendation.
GitHub Issues are preferred for discussion of this specification. Alternatively, you can send comments to our mailing list. Please send them topublic-json-ld-wg@w3.org (archives).
Please see the Working Group'simplementation report.
This document has been reviewed by W3C Members, by software developers, and by other W3C groups and interested parties, and is endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited from another document. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.
This document was produced by a group operating under theW3C Patent Policy.W3C maintains apublic 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 containsEssential Claim(s) must disclose the information in accordance withsection 6 of the W3C Patent Policy.
This document is governed by the1 March 2019 W3C Process Document.
Set of Documents
This document is one of three JSON-LD 1.1 Recommendations produced by theJSON-LD Working Group:
Table of Contents
- 1. Introduction
- 2. Conformance
- 3. Basic Concepts
- 4. Advanced Concepts
- 4.1 Advanced Context Usage
- 4.1.1 JSON-LD 1.1 Processing Mode
- 4.1.2 Default Vocabulary
- 4.1.3 Base IRI
- 4.1.4 Using the Document Base for the Default Vocabulary
- 4.1.5 Compact IRIs
- 4.1.6 Aliasing Keywords
- 4.1.7 IRI Expansion within a Context
- 4.1.8 Scoped Contexts
- 4.1.9 Context Propagation
- 4.1.10 Imported Contexts
- 4.1.11 Protected Term Definitions
- 4.2 Describing Values
- 4.3 Value Ordering
- 4.4 Nested Properties
- 4.5 Embedding
- 4.6 Indexed Values
- 4.7 Included Nodes
- 4.8 Reverse Properties
- 4.9 Named Graphs
- 4.10 Loading Documents
- 4.1 Advanced Context Usage
- 5. Forms of JSON-LD
- 6. Modifying Behavior with Link Relationships
- 7. Embedding JSON-LD in HTML Documents
- 8. Data Model
- 9. JSON-LD Grammar
- 10. Relationship to RDF
- 10.1 Serializing/Deserializing RDF
- 10.2 The rdf:JSON Datatype
- 10.3 The i18n Namespace
- 10.4 The rdf:CompoundLiteral class and the rdf:language and rdf:direction properties
- 11. Security Considerations
- 12. Privacy Considerations
- 13. Internationalization Considerations
- A. Image Descriptions
- A.1 Linked Data Dataset
- B. Relationship to Other Linked Data Formats
- B.1 Turtle
- B.2 RDFa
- B.3 Microdata
- C. IANA Considerations
- C.1 Examples
- D. Open Issues
- E. Changes since 1.0 Recommendation of 16 January 2014
- F. Changes since JSON-LD Community Group Final Report
- G. Changes since Candidate Release of 12 December 2019
- H. Changes since Proposed Recommendation Release of 7 May 2020
- I. Acknowledgements
- J. References
- J.1 Normative references
- J.2 Informative references
1. Introduction
This section is non-normative.
Linked Data [LINKED-DATA] is a way to create a network of standards-based machine interpretable data across different documents and Web sites. It allows an application to start at one piece of Linked Data, and follow embedded links to other pieces of Linked Data that are hosted on different sites across the Web.
JSON-LD is a lightweight syntax to serialize Linked Data in JSON [RFC8259]. Its design allows existing JSON to be interpreted as Linked Data with minimal changes. JSON-LD is primarily intended to be a way to use Linked Data in Web-based programming environments, to build interoperable Web services, and to store Linked Data in JSON-based storage engines. Since JSON-LD is 100% compatible with JSON, the large number of JSON parsers and libraries available today can be reused. In addition to all the features JSON provides, JSON-LD introduces:
- a universal identifier mechanism for JSON objects via the use of IRIs,
- a way to disambiguate keys shared among different JSON documents by mapping them to IRIs via a context,
- a mechanism in which a value in a JSON object may refer to a resource on a different site on the Web,
- the ability to annotate strings with their language,
- a way to associate datatypes with values such as dates and times,
- and a facility to express one or more directed graphs, such as a social network, in a single document.
JSON-LD is designed to be usable directly as JSON, with no knowledge of RDF [RDF11-CONCEPTS]. It is also designed to be usable as RDF in conjunction with other Linked Data technologies like SPARQL [SPARQL11-OVERVIEW]. Developers who require any of the facilities listed above or need to serialize an RDF graph or Dataset in a JSON-based syntax will find JSON-LD of interest. People intending to use JSON-LD with RDF tools will find it can be used as another RDF syntax, as with [Turtle] and [TriG]. Complete details of how JSON-LD relates to RDF are in section § 10. Relationship to RDF.
The syntax is designed to not disturb already deployed systems running on JSON, but provide a smooth upgrade path from JSON to JSON-LD. Since the shape of such data varies wildly, JSON-LD features mechanisms to reshape documents into a deterministic structure which simplifies their processing.
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:
- Software developers who want to encode Linked Data in a variety of programming languages that can use JSON
- Software developers who want to convert existing JSON to JSON-LD
- Software developers who want to understand the design decisions and language syntax for JSON-LD
- Software developers who want to implement processors and APIs for JSON-LD
- Software developers who want to generate or consume Linked Data, an RDF graph, or an RDF Dataset in a JSON syntax
A companion document, the JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API], specifies how to work with JSON-LD at a higher level by providing a standard library interface for common JSON-LD operations.
To understand the basics in this specification you must first be familiar withJSON, which is detailed in [RFC8259].
This document almost exclusively uses the term IRI (Internationalized Resource Indicator) when discussing hyperlinks. Many Web developers are more familiar with the URL (Uniform Resource Locator) terminology. The document also uses, albeit rarely, the URI (Uniform Resource Indicator) terminology. While these terms are often used interchangeably among technical communities, they do have important distinctions from one another and the specification goes to great lengths to try and use the proper terminology at all times.
This document can highlight changes since the JSON-LD 1.0 version. Select to changes.
1.2 Contributing
This section is non-normative.
There are a number of ways that one may participate in the development of this specification:
- Technical discussion typically occurs on the working group mailing list:public-json-ld-wg@w3.org
- The working group uses #json-ld IRC channel is available for real-time discussion on irc.w3.org.
- The #json-ld IRC channel is also available for real-time discussion on irc.freenode.net.
1.3 Typographical conventions
This section is non-normative.
The following typographic conventions are used in this specification:
markup
Markup (elements, attributes, properties), machine processable values (string, characters, media types), property name, or a file name is in red-orange monospace font.
variable
A variable in pseudo-code or in an algorithm description is in italics.
definition
A definition of a term, to be used elsewhere in this or other specifications, is in bold and italics.
A reference to a definition in this document is underlined and is also an active link to the definition itself.
A references to a definition in this document, when the reference itself is also a markup, is underlined, red-orange monospace font, and is also an active link to the definition itself.
external definition reference
A reference to a definition in another document is underlined, in italics, and is also an active link to the definition itself.
markup external definition reference
A reference to a definition in another document, when the reference itself is also a markup, is underlined, in italics red-orange monospace font, and is also an active link to the definition itself.
hyperlink
A hyperlink is underlined and in blue.
[reference]
A document reference (normative or informative) is enclosed in square brackets and links to the references section.
Changes from Recommendation
Sections or phrases changed from the previous Recommendation may be highlighted using a control in § 1.1 How to Read this Document.
Note
Notes are in light green boxes with a green left border and with a "Note" header in green. Notes are always informative.
Examples are in light khaki boxes, with khaki left border, and with a numbered "Example" header in khaki. Examples are always informative. The content of the example is in monospace font and may be syntax colored.
Examples may have tabbed navigation buttons to show the results of transforming an example into other representations.
1.4 Terminology
This section is non-normative.
This document uses the following terms as defined in external specifications and defines terms specific to JSON-LD.
Terms imported from Other Specifications
Terms imported from ECMAScript Language Specification [ECMASCRIPT], The JavaScript Object Notation (JSON) Data Interchange Format [RFC8259], Infra Standard [INFRA], and Web IDL [WEBIDL]
In the JSON serialization, an array structure is represented as square brackets surrounding zero or more values. Values are separated by commas. In the internal representation, a list (also called an array) is an ordered collection of zero or more values. While JSON-LD uses the same array representation as JSON, the collection is unordered by default. While order is preserved in regular JSON arrays, it is not in regular JSON-LD arrays unless specifically defined (see the Sets and Lists section of JSON-LD 1.1.
The values true and false that are used to express one of two possible states.
In the JSON serialization, an object structure is represented as a pair of curly brackets surrounding zero or more name/value pairs (or members). 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. In JSON-LD the names in an object must be unique.
In the internal representation a JSON object is described as amap (see [INFRA]), composed of entries with key/value pairs.
In the Application Programming Interface, a map is described using a [WEBIDL] record.
The use of the null value within JSON-LD is used to ignore or reset values. A map entry in the @context where the value, or the @id of the value, is null, explicitly decouples a term's association with an IRI. A map entry in the body of a JSON-LD document whose value is null has the same meaning as if the map entry was not defined. If @value, @list, or @set is set to null in expanded form, then the entire JSON object is ignored.
In the JSON serialization, a number is similar to that used in most programming languages, except that the octal and hexadecimal formats are not used and that leading zeros are not allowed. In the internal representation, a number is equivalent to either a long or double, depending on if the number has a non-zero fractional part (see [WEBIDL]).
A scalar is either a string, number, true, or false.
A string is a sequence of zero or more Unicode (UTF-8) characters, wrapped in double quotes, using backslash escapes (if necessary). A character is represented as a single character string.
Terms imported from Internationalized Resource Identifiers (IRIs) [RFC3987]
The absolute form of an IRI containing a scheme along with a path and optional query and fragment segments.
Denotes the common usage of an Internationalized Resource Identifier. An IRI reference may be absolute orrelative. However, the "IRI" that results from such a reference only includes absolute IRIs; any relative IRI references are resolved to their absolute form.
A relative IRI reference is an IRI reference that is relative to some other IRI, typically the base IRI of the document. Note that properties, values of @type, and values of terms defined to be vocabulary relative are resolved relative to the vocabulary mapping, not the base IRI.
Terms imported from RDF 1.1 Concepts and Abstract Syntax [RDF11-CONCEPTS], RDF Schema 1.1 [RDF-SCHEMA], and Linked Data Design Issues [LINKED-DATA]
The base IRI is an IRI established in the context, or is based on the JSON-LD document location. The base IRI is used to turn relative IRI references into IRIs.
A node in a graph that is neither an IRI, nor a literal. A blank node does not contain a de-referenceable identifier because it is either ephemeral in nature or does not contain information that needs to be linked to from outside of the linked data graph. In JSON-LD, a blank node is assigned an identifier starting with the prefix _:.
A blank node identifier is a string that can be used as an identifier for a blank node within the scope of a JSON-LD document. Blank node identifiers begin with _:.
A dataset representing a collection of RDF graphs including exactly one default graph and zero or more named graphs.
A datatype IRI is an IRI identifying a datatype that determines how the lexical form maps to aliteral value.
The default graph of a dataset is an RDF graph having no name, which may be empty.
The IRI or blank node identifying a named graph.
A language-tagged string consists of a string and a non-empty language tag as defined by [BCP47]. The language tag must be well-formed according to section 2.2.9 Classes of Conformance of [BCP47].Processors may normalize language tags to lowercase.
A set of documents, each containing a representation of a linked data graph or dataset.
A list is an ordered sequence of IRIs, blank nodes, and literals.
An object expressed as a value such as a string or number. Implicitly or explicitly includes a datatype IRI and, if the datatype is rdf:langString, an optional language tag.
A named graph is a linked data graph that is identified by an IRI or blank node.
A node in an RDF graph, either the subject and object of at least one triple. Note that a node can play both roles (subject and object) in a graph, even in the same triple.
An object is a node in a linked data graph with at least one incoming edge.
The name of a directed-arc in a linked data graph. Every property is directional and is labeled with an IRI or a blank node identifier. Whenever possible, a property should be labeled with an IRI.
Note
The use of blank node identifiers to label properties is obsolete, and may be removed in a future version of JSON-LD.
Also, see predicate in [RDF11-CONCEPTS].
A labeled directed graph, i.e., a set of nodes connected by directed-arcs. Also called linked data graph.
A resource denoted by an IRI, a blank node or literal representing something in the world (the "universe of discourse").
A subject is a node in a linked data graph with at least one outgoing edge, related to an object node through a property.
A component of an RDF graph including a subject, predicate, and object, which represents a node-arc-node segment of an RDF graph.
JSON-LD Specific Term Definitions
active context
A context that is used to resolve terms while the processing algorithm is running.
base direction
The base direction is the direction used when a string does not have a direction associated with it directly. It can be set in the context using the @direction key whose value must be one of the strings "ltr", "rtl", or null. See the Context Definitions section of JSON-LD 1.1 for a normative description.
compact IRI
A compact IRI has the form of prefix:suffix and is used as a way of expressing an IRI without needing to define separate term definitions for each IRI contained within a common vocabulary identified by prefix.
context
A set of rules for interpreting a JSON-LD document as described in the The Context section of JSON-LD 1.1, and normatively specified in the Context Definitions section of JSON-LD 1.1.
default language
The default language is the language used when a string does not have a language associated with it directly. It can be set in the context using the @language key whose value must be a string representing a [BCP47] language code or null. See the Context Definitions section of JSON-LD 1.1 for a normative description.
default object
A default object is a map that has a @default key.
embedded context
An embedded context is a context which appears as the @context entry of one of the following: a node object, a value object, a graph object, a list object, a set object, the value of a nested properties, or the value of an expanded term definition. Its value may be a map for a context definition, as an IRI, or as an array combining either of the above.
expanded term definition
An expanded term definition is a term definition where the value is a map containing one or more keyword keys to define the associated IRI, if this is a reverse property, the type associated with string values, and a container mapping. See the Expanded Term Definition section of JSON-LD 1.1 for a normative description.
A JSON-LD document, which describes the form for transforming another JSON-LD document using matching and embedding rules. A frame document allows additional keywords and certain map entries to describe the matching and transforming process.
A frame object is a map element within a frame which represents a specific portion of the frame matching either a node object or a value object in the input. See the Frame Objects section of JSON-LD 1.1 for a normative description.
graph object
A graph object represents a named graph as the value of a map entry within a node object. When expanded, a graph object must have an @graph entry, and may also have @id, and @index entries. A simple graph object is a graph object which does not have an @id entry. Note that node objects may have a @graph entry, but are not considered graph objects if they include any other entries. A top-level object consisting of @graph is also not a graph object. Note that a node object may also represent a named graph it it includes other properties. See the Graph Objects section of JSON-LD 1.1 for a normative description.
id map
An id map is a map value of a term defined with @container set to @id. The values of the id map must be node objects, and its keys are interpreted as IRIs representing the @id of the associated node object. If a value in the id map contains a key expanding to @id, its value must be equivalent to the referencing key in the id map. See the Id Maps section of JSON-LD 1.1 for a normative description.
implicitly named graph
A named graph created from the value of a map entry having an expanded term definition where @container is set to @graph.
included block
An included block is an entry in a node object where the key is either @included or an alias of @included and the value is one or more node objects. See the Included Blocks section of JSON-LD 1.1 for a normative description.
index map
An index map is a map value of a term defined with @container set to @index, whose values must be any of the following types:string,number,true,false,null,node object,value object,list object,set object, or an array of zero or more of the above possibilities. See the Index Maps section in JSON-LD 1.1 for a formal description.
JSON literal
A JSON literal is a literal where the associated datatype IRI is rdf:JSON. In the value object representation, the value of @type is @json. JSON literals represent values which are valid JSON [RFC8259]. See the The rdf:JSON Datatype section in JSON-LD 1.1 for a normative description.
JSON-LD document
A JSON-LD document is a serialization of an RDF dataset. See the JSON-LD Grammar section in JSON-LD 1.1 for a formal description.
JSON-LD internal representation
The JSON-LD internal representation is the result of transforming a JSON syntactic structure into the core data structures suitable for direct processing:arrays, maps, strings, numbers, booleans, and null.
A JSON-LD Processor is a system which can perform the algorithms defined in JSON-LD 1.1 Processing Algorithms and API. See the Conformance section in JSON-LD 1.1 API for a formal description.
JSON-LD value
A JSON-LD value is a string, a number,true or false, a typed value, or a language-tagged string. It represents an RDF literal.
keyword
A string that is specific to JSON-LD, described in the Syntax Tokens and Keywords section of JSON-LD 1.1, and normatively specified in the Keywords section of JSON-LD 1.1,
language map
An language map is a map value of a term defined with @container set to @language, whose keys must be strings representing [BCP47] language codes and the values must be any of the following types:null,string, or an array of zero or more of the above possibilities. See the Language Maps section of JSON-LD 1.1 for a normative description.
list object
A list object is a map that has a @list key. It may also have an @index key, but no other entries. See the Lists and Sets section of JSON-LD 1.1 for a normative description.
local context
A context that is specified with a map, specified via the @context keyword.
nested property
A nested property is a key in a node object whose value is a map containing entries which are treated as if they were values of the node object. The nested property itself is semantically meaningless and used only to create a sub-structure within a node object. See the Property Nesting section of JSON-LD 1.1 for a normative description.
node object
A node object represents zero or more properties of a node in the graph serialized by the JSON-LD document. A map is a node object if it exists outside of the JSON-LD context and:
- it does not contain the
@value,@list, or@setkeywords, or - it is not the top-most map in the JSON-LD document consisting of no other entries than
@graphand@context. The entries of a node object whose keys are not keywords are also called properties of the node object. See the Node Objects section of JSON-LD 1.1 for a normative description.
node reference
A node object used to reference a node having only the @id key.
prefix
A prefix is the first component of a compact IRI which comes from a term that maps to a string that, when prepended to the suffix of the compact IRI, results in an IRI.
processing mode
The processing mode defines how a JSON-LD document is processed. By default, all documents are assumed to be conformant with this specification. By defining a different version using the @version entry in a context, publishers can ensure that processors conformant with JSON-LD 1.0 [JSON-LD10] will not accidentally process JSON-LD 1.1 documents, possibly creating a different output. The API provides an option for setting the processing mode to json-ld-1.0, which will prevent JSON-LD 1.1 features from being activated, or error if @version entry in a context is explicitly set to 1.1. This specification extends JSON-LD 1.0 via the json-ld-1.1 processing mode.
scoped context
A scoped context is part of an expanded term definition using the@context entry. It has the same form as an embedded context. When the term is used as a type, it defines a type-scoped context, when used as a property it defines a property-scoped context.
set object
A set object is a map that has an @set entry. It may also have an @index key, but no other entries. See the Lists and Sets section of JSON-LD 1.1 for a normative description.
term
A term is a short word defined in a context that may be expanded to an IRI. See the Terms section of JSON-LD 1.1 for a normative description.
term definition
A term definition is an entry in a context, where the key defines a term which may be used within a map as a key, type, or elsewhere that a string is interpreted as a vocabulary item. Its value is either a string (simple term definition), expanding to an IRI, or a map (expanded term definition).
type map
A type map is a map value of a term defined with @container set to @type, whose keys are interpreted as IRIs representing the @type of the associated node object; the value must be a node object, or array of node objects. If the value contains a term expanding to @type, its values are merged with the map value when expanding. See the Type Maps section of JSON-LD 1.1 for a normative description.
typed value
A typed value consists of a value, which is a string, and a type, which is an IRI.
value object
A value object is a map that has an @value entry. See the Value Objects section of JSON-LD 1.1 for a normative description.
vocabulary mapping
The vocabulary mapping is set in the context using the @vocab key whose value must be an IRI, a compact IRI, a term, or null. See the Context Definitions section of JSON-LD 1.1 for a normative description.
1.5 Design Goals and Rationale
This section is non-normative.
JSON-LD satisfies the following design goals:
Simplicity
No extra processors or software libraries are necessary to use JSON-LD in its most basic form. The language provides developers with a very easy learning curve. Developers not concerned with Linked Data only need to understand JSON, and know to include but ignore the @context property, to use the basic functionality in JSON-LD.
Compatibility
A JSON-LD document is always a valid JSON document. This ensures that all of the standard JSON libraries work seamlessly with JSON-LD documents.
Expressiveness
The syntax serializes labeled directed graphs. This ensures that almost every real world data model can be expressed.
Terseness
The JSON-LD syntax is very terse and human readable, requiring as little effort as possible from the developer.
Zero Edits, most of the time
JSON-LD ensures a smooth and simple transition from existing JSON-based systems. In many cases, zero edits to the JSON document and the addition of one line to the HTTP response should suffice (see § 6.1 Interpreting JSON as JSON-LD). This allows organizations that have already deployed large JSON-based infrastructure to use JSON-LD's features in a way that is not disruptive to their day-to-day operations and is transparent to their current customers. However, there are times where mapping JSON to a graph representation is a complex undertaking. In these instances, rather than extending JSON-LD to support esoteric use cases, we chose not to support the use case. While Zero Edits is a design goal, it is not always possible without adding great complexity to the language. JSON-LD focuses on simplicity when possible.
Usable as RDF
JSON-LD is usable by developers as idiomatic JSON, with no need to understand RDF [RDF11-CONCEPTS]. JSON-LD is also usable as RDF, so people intending to use JSON-LD with RDF tools will find it can be used like any other RDF syntax. Complete details of how JSON-LD relates to RDF are in section§ 10. Relationship to RDF.
1.6 Data Model Overview
This section is non-normative.
Generally speaking, the data model described by a JSON-LD document is a labeled, directed graph. The graph contains nodes, which are connected by directed-arcs. A node is either a resource with properties, or the data values of those properties includingstrings, numbers, typed values (like dates and times) and IRIs.
Within a directed graph, nodes are resources, and may be unnamed, i.e., not identified by an IRI; which are called blank nodes, and may be identified using a blank node identifier. These identifiers may be required to represent a fully connected graph using a tree structure, such as JSON, but otherwise have no intrinsic meaning. Literal values, such as strings and numbers, are also considered resources, and JSON-LD distinguishes between node objects and value objects to distinguish between the different kinds of resource.
This simple data model is incredibly flexible and powerful, capable of modeling almost any kind of data. For a deeper explanation of the data model, see section § 8. Data Model.
Developers who are familiar with Linked Data technologies will recognize the data model as the RDF Data Model. To dive deeper into how JSON-LD and RDF are related, see section § 10. Relationship to RDF.
At the surface level, a JSON-LD document is simplyJSON, detailed in [RFC8259]. For the purpose of describing the core data structures, this is limited to arrays, maps (the parsed version of a JSON Object),strings, numbers, booleans, and null,called the JSON-LD internal representation. This allows surface syntaxes other than JSON to be manipulated using the same algorithms, when the syntax maps to equivalent core data structures.
1.7 Syntax Tokens and Keywords
This section is non-normative.
JSON-LD specifies a number of syntax tokens and keywords that are a core part of the language. A normative description of the keywords is given in § 9.16 Keywords.
:
The separator for JSON keys and values that use compact IRIs.
@base
Used to set the base IRI against which to resolve those relative IRI references which are otherwise interpreted relative to the document. This keyword is described in § 4.1.3 Base IRI.
@container
Used to set the default container type for a term. This keyword is described in the following sections:
- § 4.3 Value Ordering,
- § 4.6.1 Data Indexing,
- § 4.6.2 Language Indexing,
- § 4.6.3 Node Identifier Indexing,
- § 4.6.4 Node Type Indexing
- § 4.9 Named Graphs,
- § 4.9.3 Named Graph Indexing, and
- § 4.9.2 Named Graph Data Indexing
@context
Used to define the short-hand names that are used throughout a JSON-LD document. These short-hand names are called terms and help developers to express specific identifiers in a compact manner. The@context keyword is described in detail in§ 3.1 The Context.
@direction
Used to set the base direction of a JSON-LD value, which are not typed values (e.g. strings, or language-tagged strings). This keyword is described in§ 4.2.4 String Internationalization.
@graph
Used to express a graph. This keyword is described in § 4.9 Named Graphs.
@id
Used to uniquely identify node objects that are being described in the document with IRIs orblank node identifiers. This keyword is described in § 3.3 Node Identifiers. A node reference is a node object containing only the @id property, which may represent a reference to a node object found elsewhere in the document.
@import
Used in a context definition to load an external context within which the containing context definition is merged. This can be useful to add JSON-LD 1.1 features to JSON-LD 1.0 contexts.
@included
Used in a top-level node object to define an included block, for including secondary node objects within another node object.
@index
Used to specify that a container is used to index information and that processing should continue deeper into a JSON data structure. This keyword is described in § 4.6.1 Data Indexing.
@json
Used as the @type value of a JSON literal. This keyword is described in § 4.2.2 JSON Literals.
@language
Used to specify the language for a particular string value or the default language of a JSON-LD document. This keyword is described in§ 4.2.4 String Internationalization.
@list
Used to express an ordered set of data. This keyword is described in § 4.3.1 Lists.
@nest
Used to define a property of a node object that groups together properties of that node, but is not an edge in the graph.
@none
Used as an index value in an index map, id map, language map, type map, or elsewhere where a map is used to index into other values, when the indexed node does not have the feature being indexed.
@prefix
With the value true, allows this term to be used to construct a compact IRI when compacting. With the value false prevents the term from being used to construct a compact IRI. Also determines if the term will be considered when expanding compact IRIs.
@propagate
Used in a context definition to change the scope of that context. By default, it is true, meaning that contexts propagate across node objects (other than for type-scoped contexts, which default to false). Setting this to false causes term definitions created within that context to be removed when entering a new node object.
@protected
Used to prevent term definitions of a context to be overridden by other contexts. This keyword is described in § 4.1.11 Protected Term Definitions.
@reverse
Used to express reverse properties. This keyword is described in§ 4.8 Reverse Properties.
@set
Used to express an unordered set of data and to ensure that values are always represented as arrays. This keyword is described in§ 4.3.2 Sets.
@type
Used to set the type of a node or the datatype of a typed value. This keyword is described further in § 3.5 Specifying the Type and § 4.2.1 Typed Values.
Note
The use of @type to define a type for bothnode objects and value objects addresses the basic need to type data, be it a literal value or a more complicated resource. Experts may find the overloaded use of the @type keyword for both purposes concerning, but should note that Web developer usage of this feature over multiple years has not resulted in its misuse due to the far less frequent use of @type to express typed literal values.
@value
Used to specify the data that is associated with a particularproperty in the graph. This keyword is described in§ 4.2.4 String Internationalization and§ 4.2.1 Typed Values.
@version
Used in a context definition to set the processing mode. New features since JSON-LD 1.0 [JSON-LD10] described in this specification are not available when processing mode has been explicitly set tojson-ld-1.0.
Note
Within a context definition @version takes the specific value 1.1, not"json-ld-1.1", as a JSON-LD 1.0 processor may accept a string value for @version, but will reject a numeric value.
Note
The use of 1.1 for the value of @version is intended to cause a JSON-LD 1.0 processor to stop processing. Although it is clearly meant to be related to JSON-LD 1.1, it does not otherwise adhere to the requirements for Semantic Versioning.
@vocab
Used to expand properties and values in @type with a common prefixIRI. This keyword is described in § 4.1.2 Default Vocabulary.
All keys, keywords, and values in JSON-LD are case-sensitive.
2. Conformance
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words MAY, MUST, MUST NOT, RECOMMENDED, SHOULD, and SHOULD NOT in this document are to be interpreted as described inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
A JSON-LD document complies with this specification if it follows the normative statements in appendix § 9. JSON-LD Grammar. JSON documents can be interpreted as JSON-LD by following the normative statements in§ 6.1 Interpreting JSON as JSON-LD. For convenience, normative statements for documents are often phrased as statements on the properties of the document.
This specification makes use of the following namespace prefixes:
| Prefix | IRI |
|---|---|
| dc11 | http://purl.org/dc/elements/1.1/ |
| dcterms | http://purl.org/dc/terms/ |
| cred | https://w3id.org/credentials# |
| foaf | http://xmlns.com/foaf/0.1/ |
| geojson | https://purl.org/geojson/vocab# |
| prov | http://www.w3.org/ns/prov# |
| i18n | https://www.w3.org/ns/i18n# |
| rdf | http://www.w3.org/1999/02/22-rdf-syntax-ns# |
| schema | http://schema.org/ |
| skos | http://www.w3.org/2004/02/skos/core# |
| xsd | http://www.w3.org/2001/XMLSchema# |
These are used within this document as part of a compact IRI as a shorthand for the resulting IRI, such as dcterms:title used to represent http://purl.org/dc/terms/title.
3. Basic Concepts
This section is non-normative.
JSON [RFC8259] is a lightweight, language-independent data interchange format. It is easy to parse and easy to generate. However, it is difficult to integrate JSON from different sources as the data may contain keys that conflict with other data sources. Furthermore, JSON has no built-in support for hyperlinks, which are a fundamental building block on the Web. Let's start by looking at an example that we will be using for the rest of this section:
: Sample JSON document
{
"name": "Manu Sporny",
"homepage": "http://manu.sporny.org/",
"image": "http://manu.sporny.org/images/manu.png"
}It's obvious to humans that the data is about a person whosename is "Manu Sporny" and that the homepage property contains the URL of that person's homepage. A machine doesn't have such an intuitive understanding and sometimes, even for humans, it is difficult to resolve ambiguities in such representations. This problem can be solved by using unambiguous identifiers to denote the different concepts instead of tokens such as "name", "homepage", etc.
Linked Data, and the Web in general, uses IRIs (Internationalized Resource Identifiers as described in [RFC3987]) for unambiguous identification. The idea is to use IRIs to assign unambiguous identifiers to data that may be of use to other developers. It is useful for terms, like name and homepage, to expand to IRIs so that developers don't accidentally step on each other's terms. Furthermore, developers and machines are able to use this IRI (by using a web browser, for instance) to go to the term and get a definition of what the term means. This process is known as IRI dereferencing.
Leveraging the popular schema.org vocabulary, the example above could be unambiguously expressed as follows:
In the example above, every property is unambiguously identified by an IRI and all values representing IRIs are explicitly marked as such by the@id keyword. While this is a valid JSON-LD document that is very specific about its data, the document is also overly verbose and difficult to work with for human developers. To address this issue, JSON-LD introduces the notion of a context as described in the next section.
This section only covers the most basic features of JSON-LD. More advanced features, including typed values, indexed values, and named graphs, can be found in § 4. Advanced Concepts.
3.1 The Context
This section is non-normative.
When two people communicate with one another, the conversation takes place in a shared environment, typically called "the context of the conversation". This shared context allows the individuals to use shortcut terms, like the first name of a mutual friend, to communicate more quickly but without losing accuracy. A context in JSON-LD works in the same way. It allows two applications to use shortcut terms to communicate with one another more efficiently, but without losing accuracy.
Simply speaking, a context is used to map terms to IRIs.Terms are case sensitive and most valid strings that are not reserved JSON-LD keywords can be used as a term.Exceptions are the empty string "" and strings that have the form of a keyword (i.e., starting with "@" followed exclusively by one or more ALPHA characters (see [RFC5234])), which must not be used as terms. Strings that have the form of an IRI (e.g., containing a ":") should not be used as terms.
For the sample document in the previous section, a context would look something like this:
: Context for the sample document in the previous section
{ "@context": { "name": "http://schema.org/name",
"image": {
"@id": "http://schema.org/image",
"@type": "@id"
},
"homepage": {
"@id": "http://schema.org/url",
"@type": "@id"
}} }
As the context above shows, the value of a term definition can either be a simple string, mapping the term to an IRI, or a map.
A context is introduced using an entry with the key @context and may appear within a node object or a value object.
When an entry with a term key has a map value, the map is called an expanded term definition. The example above specifies that the values of image and homepage, if they are strings, are to be interpreted asIRIs. Expanded term definitions also allow terms to be used for index maps and to specify whether array values are to be interpreted as sets or lists.Expanded term definitions may be defined using IRIs orcompact IRIs as keys, which is mainly used to associate type or language information with anIRIs or compact IRI.
Contexts can either be directly embedded into the document (an embedded context) or be referenced using a URL. Assuming the context document in the previous example can be retrieved at https://json-ld.org/contexts/person.jsonld, it can be referenced by adding a single line and allows a JSON-LD document to be expressed much more concisely as shown in the example below:
The referenced context not only specifies how the terms map toIRIs in the Schema.org vocabulary but also specifies that string values associated with the homepage and image property can be interpreted as an IRI ("@type": "@id", see § 3.2 IRIs for more details). This information allows developers to re-use each other's data without having to agree to how their data will interoperate on a site-by-site basis. 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. Information contained outside of the @context value is ignored when the document is used as an external JSON-LD context document.
A remote context may also be referenced using a relative URL, which is resolved relative to the location of the document containing the reference. For example, if a document were located at http://example.org/document.jsonld and contained a relative reference to context.jsonld, the referenced context document would be found relative at http://example.org/context.jsonld.
: Loading a relative context
{ "@context": "context.jsonld", "name": "Manu Sporny", "homepage": "http://manu.sporny.org/", "image": "http://manu.sporny.org/images/manu.png" }
Note
Resolution of relative references to context URLs also applies to remote context documents, as they may themselves contain references to other contexts.
JSON documents can be interpreted as JSON-LD without having to be modified by referencing a context via an HTTP Link Header as described in § 6.1 Interpreting JSON as JSON-LD. It is also possible to apply a custom context using the JSON-LD 1.1 API [JSON-LD11-API].
In JSON-LD documents,contexts may also be specified inline. This has the advantage that documents can be processed even in the absence of a connection to the Web. Ultimately, this is a modeling decision and different use cases may require different handling. See Security Considerations in § C. IANA Considerations for a discussion on using remote contexts.
This section only covers the most basic features of the JSON-LD Context. The Context can also be used to help interpret other more complex JSON data structures, such as indexed values,ordered values, andnested properties. More advanced features related to the JSON-LD Context are covered in§ 4. Advanced Concepts.
3.2 IRIs
This section is non-normative.
IRIs (Internationalized Resource Identifiers [RFC3987]) are fundamental to Linked Data as that is how mostnodes and properties are identified. In JSON-LD, IRIs may be represented as an IRI reference. An IRI is defined in [RFC3987] as containing a_scheme_ along with path and optional query and_fragment_ segments. A relative IRI reference is an IRI that is relative to some other IRI. In JSON-LD, with exceptions that are as described below, all relative IRI references are resolved relative to the base IRI.
Note
As noted in § 1.1 How to Read this Document, IRIs can often be confused with URLs (Uniform Resource Locators), the primary distinction is that a URL locates a resource on the web, an IRI identifies a resource. While it is a good practice for resource identifiers to be dereferenceable, sometimes this is not practical. In particular, note the [URN] scheme for Uniform Resource Names, such as UUID. An example UUID is urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6.
A string is interpreted as an IRI when it is the value of a map entry with the key @id:
: Values of @id are interpreted as IRI
{
"homepage": { "@id": "http://example.com/" }
}
Values that are interpreted as IRIs, can also be expressed as relative IRI references. For example, assuming that the following document is located athttp://example.com/about/, the relative IRI reference ../ would expand to http://example.com/ (for more information on where relative IRI references can be used, please refer to section § 9. JSON-LD Grammar).
: IRIs can be relative
{
"homepage": { "@id": "../" }
}
IRIs can be expressed directly in the key position like so:
{
"http://schema.org/name": "Manu Sporny" }
In the example above, the key http://schema.org/name is interpreted as an IRI.
Term-to-IRI expansion occurs if the key matches a term defined within the active context:
JSON keys that do not expand to an IRI, such as status in the example above, are not Linked Data and thus ignored when processed.
If type coercion rules are specified in the @context for a particular term or property IRI, an IRI is generated:
In the example above, since the value http://manu.sporny.org/ is expressed as a JSON string, the type coercion rules will transform the value into an IRI when processing the data. See § 4.2.3 Type Coercion for more details about this feature.
In summary, IRIs can be expressed in a variety of different ways in JSON-LD:
- Map entries that have a key mapping to a term in the active context expand to an IRI (only applies outside of the context definition).
- An IRI is generated for the string value specified using
@idor@type. - An IRI is generated for the string value of any key for which there are coercion rules that contain an
@typekey that is set to a value of@idor@vocab.
This section only covers the most basic features associated with IRIs in JSON-LD. More advanced features related to IRIs are covered in section § 4. Advanced Concepts.
3.3 Node Identifiers
This section is non-normative.
To be able to externally reference nodes in an RDF graph, it is important thatnodes have an identifier. IRIs are a fundamental concept of Linked Data, fornodes to be truly linked, dereferencing the identifier should result in a representation of that node. This may allow an application to retrieve further information about anode.
In JSON-LD, a node is identified using the @id keyword:
The example above contains a node object identified by the IRI http://me.markus-lanthaler.com/.
This section only covers the most basic features associated with node identifiers in JSON-LD. More advanced features related to node identifiers are covered in section § 4. Advanced Concepts.
3.4 Uses of JSON Objects
This section is non-normative.
As a syntax, JSON has only a limited number of syntactic elements:
- Numbers, which describe literal numeric values,
- Strings, which may describe literal string values, or be used as the keys in a JSON object.
- Boolean
trueandfalse, which describe literal boolean values, null, which describes the absence of a value,- Arrays, which describe an ordered set of values of any type, and
- JSON objects, which provide a set of map entries, relating keys with values.
The JSON-LD data model allows for a richer set of resources, based on the RDF data model. The data model is described more fully in § 8. Data Model. JSON-LD uses JSON objects to describe various resources, along with the relationships between these resources:
Node objects are used to define nodes in the linked data graph which may have both incoming and outgoing edges. Node objects are principle structure for defining resources having properties. See § 9.2 Node Objects for the normative definition.
Value objects are used for describing literal nodes in a linked data graph which may have only incoming edges. In JSON, some literal nodes may be described without the use of a JSON object (e.g., numbers, strings, and boolean values), but in the expanded form, all literal nodes are described using value objects. See § 4.2 Describing Values for more information, and § 9.5 Value Objects for the normative definition.
List Objects are a special kind of JSON-LD maps, distinct from node objects and value objects, used to express ordered values by wrapping an array in a map under the key @list.Set Objects exist for uniformity, and are equivalent to the array value of the @set key. See § 4.3.1 Lists and § 4.3.2 Sets for more detail.
Map Objects
JSON-LD uses various forms of maps as ways to more easily access values of a property.
Allows multiple values differing in their associated language to be indexed by language tag. See § 4.6.2 Language Indexing for more information, and § 9.8 Language Maps for the normative definition.
Allows multiple values (node objects or value objects) to be indexed by an associated @index. See § 4.6.1 Data Indexing for more information, and § 9.9 Index Maps for the normative definition.
Allows multiple node objects to be indexed by an associated @id. See § 4.6.3 Node Identifier Indexing for more information, and § 9.11 Id Maps for the normative definition.
Allows multiple node objects to be indexed by an associated @type. See § 4.6.4 Node Type Indexing for more information, and § 9.12 Type Maps for the normative definition.
Named Graph Indexing
Allows multiple named graphs to be indexed by an associated graph name. See § 4.9.3 Named Graph Indexing for more information.
A graph object is much like a node object, except that it defines a named graph. See § 4.9 Named Graphs for more information, and § 9.4 Graph Objects for the normative definition. A node object may also describe a named graph, in addition to other properties defined on the node. The notable difference is that a graph object only describes a named graph.
A Context Definition uses the JSON object form, but is not itself data in a linked data graph. A Context Definition also may contain expanded term definitions, which are also represented using JSON objects. See § 3.1 The Context,§ 4.1 Advanced Context Usage for more information, and § 9.15 Context Definitions for the normative definition.
3.5 Specifying the Type
This section is non-normative.
In Linked Data, it is common to specify the type of a graph node; in many cases, this can be inferred based on the properties used within a given node object, or the property for which a node is a value. For example, in the schema.org vocabulary, the givenName property is associated with a Person. Therefore, one may reason that if a node object contains the property givenName, that the type is a Person; making this explicit with @type helps to clarify the association.
The type of a particular node can be specified using the @type keyword. In Linked Data, types are uniquely identified with an IRI.
A node can be assigned more than one type by using an array:
The value of a @type key may also be a term defined in the active context:
In addition to setting the type of nodes,@type can also be used to set the type of a value to create a typed value. This use of @type is similar to that used to define the type of a node object, but value objects are restricted to having just a single type. The use of @type to create typed values is discussed more fully in § 4.2.1 Typed Values.
Typed values can also be defined implicitly, by specifying@type in an expanded term definition. This is covered more fully in § 4.2.3 Type Coercion.
4. Advanced Concepts
This section is non-normative.
JSON-LD has a number of features that provide functionality above and beyond the core functionality described above. JSON can be used to express data using such structures, and the features described in this section can be used to interpret a variety of different JSON structures as Linked Data. A JSON-LD processor will make use of provided and embedded contexts to interpret property values in a number of different idiomatic ways.
Describing values
One pattern in JSON is for the value of a property to be a string. Often times, this string actually represents some other typed value, for example an IRI, a date, or a string in some specific language. See § 4.2 Describing Values for details on how to describe such value typing.
Value ordering
In JSON, a property with an array value implies an implicit order; arrays in JSON-LD do not convey any ordering of the contained elements by default, unless defined using embedded structures or through a context definition. See § 4.3 Value Ordering for a further discussion.
Property nesting
Another JSON idiom often found in APIs is to use an intermediate object to group together related properties of an object; in JSON-LD these are referred to as nested properties and are described in § 4.4 Nested Properties.
Referencing objects
Linked Data is all about describing the relationships between different resources. Sometimes these relationships are between resources defined in different documents described on the web, sometimes the resources are described within the same document.
In this case, a document residing at http://manu.sporny.org/about may contain the example above, and reference another document athttps://greggkellogg.net/foaf which could include a similar representation.
A common idiom found in JSON usage is objects being specified as the value of other objects, called object embedding in JSON-LD; for example, a friend specified as an object value of a Person:
See § 4.5 Embedding details these relationships.
Indexed values
Another common idiom in JSON is to use an intermediate object to represent property values via indexing. JSON-LD allows data to be indexed in a number of different ways, as detailed in § 4.6 Indexed Values.
Reverse Properties
JSON-LD serializes directed graphs. That means that every property points from a node to another node or value. However, in some cases, it is desirable to serialize in the reverse direction, as detailed in § 4.8 Reverse Properties.
The following sections describe such advanced functionality in more detail.
4.1 Advanced Context Usage
This section is non-normative.
Section § 3.1 The Context introduced the basics of what makes JSON-LD work. This section expands on the basic principles of thecontext and demonstrates how more advanced use cases can be achieved using JSON-LD.
In general, contexts may be used any time amap is defined. The only time that one cannot express a context is as a direct child of another context definition (other than as part of an expanded term definition). For example, a JSON-LD document may have the form of an array composed of one or more node objects, which use a context definition in each top-level node object:
The outer array is standard for a document inexpanded document form and flattened document form, and may be necessary when describing a disconnected graph, where nodes may not reference each other. In such cases, using a top-level map with a @graph property can be useful for saving the repetition of @context. See § 4.5 Embedding for more.
Duplicate context terms are overridden using a most-recently-defined-wins mechanism.
In the example above, the name term is overridden in the more deeply nested details structure, which uses its own embedded context. Note that this is rarely a good authoring practice and is typically used when working with legacy applications that depend on a specific structure of themap. If a term is redefined within a context, all previous rules associated with the previous definition are removed. If a term is redefined to null, the term is effectively removed from the list ofterms defined in the active context.
Multiple contexts may be combined using an array, which is processed in order. The set of contexts defined within a specific map are referred to as local contexts. Theactive context refers to the accumulation oflocal contexts that are in scope at a specific point within the document. Setting a local context to null effectively resets the active context to an empty context, without term definitions, default language, or other things defined within previous contexts. The following example specifies an external context and then layers an embedded context on top of the external context:
In JSON-LD 1.1, there are other mechanisms for introducing contexts, including scoped contexts and imported contexts, and there are new ways of protecting term definitions, so there are cases where the last defined inline context is not necessarily one which defines the scope of terms. See § 4.1.8 Scoped Contexts,§ 4.1.9 Context Propagation,§ 4.1.10 Imported Contexts, and§ 4.1.11 Protected Term Definitions for further information.
Note
When possible, the context definition should be put at the top of a JSON-LD document. This makes the document easier to read and might make streaming parsers more efficient. Documents that do not have thecontext at the top are still conformant JSON-LD.
Note
To avoid forward-compatibility issues, terms starting with an @ characterfollowed exclusively by one or more ALPHA characters (see [RFC5234]) are to be avoided as they might be used as keyword in future versions of JSON-LD. Terms starting with an @ character that are notJSON-LD 1.1 keywords are treated as any other term, i.e., they are ignored unless mapped to an IRI. Furthermore, the use of empty terms ("") is not allowed as not all programming languages are able to handle empty JSON keys.
4.1.1 JSON-LD 1.1 Processing Mode
This section is non-normative.
New features defined in JSON-LD 1.1 are available unless the processing mode is set to json-ld-1.0. This may be set through an API option. The processing mode may be explicitly set to json-ld-1.1 using the @version entry in a context set to the value 1.1 as a number, or through an API option. Explicitly setting the processing mode to json-ld-1.1 will prohibit JSON-LD 1.0 processors from incorrectly processing a JSON-LD 1.1 document.
: Setting @version in context
{ "@context": { "@version": 1.1 } }
The first context encountered when processing a document which contains @version determines the processing mode, unless it is defined explicitly through an API option. This means that if "@version": 1.1 is encountered after processing a context without @version, the former will be interpreted as having had "@version": 1.1 defined within it.
Note
Setting the processing mode explicitly to json-ld-1.1 is RECOMMENDED to prevent a JSON-LD 1.0 processor from incorrectly processing a JSON-LD 1.1 document and producing different results.
4.1.2 Default Vocabulary
This section is non-normative.
At times, all properties and types may come from the same vocabulary. JSON-LD's@vocab keyword allows an author to set a common prefix which is used as the vocabulary mapping and is used for all properties and types that do not match a term and are neither an IRI nor a compact IRI (i.e., they do not contain a colon).
If @vocab is used but certain keys in anmap should not be expanded using the vocabulary IRI, a term can be explicitly set to null in the context. For instance, in the example below the databaseId entry would not expand to anIRI causing the property to be dropped when expanding.
Since JSON-LD 1.1, the vocabulary mapping in a local context can be set to a relative IRI reference, which is concatenated to any vocabulary mapping in the active context (see § 4.1.4 Using the Document Base for the Default Vocabulary for how this applies if there is no vocabulary mapping in the active context).
The following example illustrates the affect of expanding a property using a relative IRI reference, which is shown in the Expanded (Result) tab below.
Note
The grammar for @vocab, as defined in § 9.15 Context Definitions allows the value to be a term or compact IRI. Note that terms used in the value of @vocab must be in scope at the time the context is introduced, otherwise there would be a circular dependency between @vocab and other terms defined in the same context.
4.1.3 Base IRI
This section is non-normative.
JSON-LD allows IRIs to be specified in a relative form which is resolved against the document base accordingsection 5.1 Establishing a Base URI of [RFC3986]. The base IRI may be explicitly set with a context using the @base keyword.
For example, if a JSON-LD document was retrieved from http://example.com/document.jsonld,relative IRI references would resolve against that IRI:
: Use a relative IRI reference as node identifier
{ "@context": { "label": "http://www.w3.org/2000/01/rdf-schema#label" }, "@id": "", "label": "Just a simple document" }
This document uses an empty @id, which resolves to the document base. However, if the document is moved to a different location, the IRI would change. To prevent this without having to use an IRI, a context may define an @base mapping, to overwrite the base IRI for the document.
Setting @base to null will preventrelative IRI references from being expanded toIRIs.
Please note that the @base will be ignored if used in external contexts.
4.1.4 Using the Document Base for the Default Vocabulary
This section is non-normative.
In some cases, vocabulary terms are defined directly within the document itself, rather than in an external vocabulary. Since JSON-LD 1.1, the vocabulary mapping in a local context can be set to a relative IRI reference, which is, if there is no vocabulary mapping in scope, resolved against the base IRI. This causes terms which are expanded relative to the vocabulary, such as the keys of node objects, to be based on the base IRI to create IRIs.
: Using "#" as the vocabulary mapping
{ "@context": { "@version": 1.1, "@base": "http://example/document", "@vocab": "#" }, "@id": "http://example.org/places#BrewEats", "@type": "Restaurant", "name": "Brew Eats"
}
If this document were located at http://example/document, it would expand as follows:
4.1.5 Compact IRIs
This section is non-normative.
A compact IRI is a way of expressing an IRI using a prefix and suffix separated by a colon (:). The prefix is a term taken from theactive 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 shorthand 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 IRI for the vocabulary term. For example,foaf:name would be expanded to the IRI http://xmlns.com/foaf/0.1/name.
In the example above, foaf:name expands to the IRI http://xmlns.com/foaf/0.1/name and foaf:Person expands to http://xmlns.com/foaf/0.1/Person.
Prefixes are expanded when the form of the value is a compact IRI represented as a prefix:suffix combination, the prefix matches a term defined within theactive context, and the suffix does not begin with two slashes (//). The compact IRI is expanded by concatenating the IRI mapped to the prefix to the (possibly empty)suffix. If the prefix is not defined in the active context, or the suffix begins with two slashes (such as in http://example.com), the value is interpreted as IRI instead. If the prefix is an underscore (_), the value is interpreted as blank node identifier instead.
It's also possible to use compact IRIs within the context as shown in the following example:
When operating explicitly with the processing mode for JSON-LD 1.0 compatibility, terms may be chosen as compact IRI prefixes when compacting only if a simple term definition is used where the value ends with a URI gen-delim character (e.g, /,# and others, see [RFC3986]).
In JSON-LD 1.1, terms may be chosen as compact IRI prefixes when expanding or compacting only if a simple term definition is used where the value ends with a URI gen-delim character, or if their expanded term definition contains a @prefix entry with the value true. If a simple term definition does not end with a URI gen-delim character, or a expanded term definition contains a @prefix entry with the value false, the term will not be used for either expanding compact IRIs or compacting IRIs to compact IRIs.
Note
The term selection behavior for 1.0 processors was changed as a result of an errata against JSON-LD 1.0 reported here. This does not affect the behavior of processing existing JSON-LD documents, but creates a slight change when compacting documents using Compact IRIs.
The behavior when compacting can be illustrated by considering the following input document in expanded form:
: Expanded document used to illustrate compact IRI creation
[{
"http://example.com/vocab/property": [{"@value": "property"}],
"http://example.com/vocab/propertyOne": [{"@value": "propertyOne"}]
}]Using the following context in the 1.0 processing mode will now select the term vocab rather than_property_, even though the IRI associated with_property_ captures more of the original IRI.
: Compact IRI generation context (1.0)
{
"@context": {
"vocab": "http://example.com/vocab/",
"property": "http://example.com/vocab/property"
}
}Compacting using the previous context with the above expanded input document results in the following compacted result:
In the original [JSON-LD10], the term selection algorithm would have selected property, creating the Compact IRI property:One. The original behavior can be made explicit using @prefix:
: Compact IRI generation context (1.1)
{
"@context": {
"@version": 1.1,
"vocab": "http://example.com/vocab/",
"property": {
"@id": "http://example.com/vocab/property",
"@prefix": true
}
}
}In this case, the property term would not normally be usable as a prefix, both because it is defined with an expanded term definition, and because its @id does not end in agen-delim character. Adding"@prefix": true allows it to be used as the prefix portion of the compact IRI property:One.
4.1.6 Aliasing Keywords
This section is non-normative.
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.
In the example above, the @id and @type keywords have been given the aliasesurl and a, respectively.
Other than for @type, properties ofexpanded term definitions where the term is a keyword result in an error.Unless the processing mode is set to json-ld-1.0, there is also an exception for @type; see § 4.3.3 Using @set with @type for further details and usage examples.
Unless the processing mode is set to json-ld-1.0, aliases of keywords are either simple term definitions, where the value is a keyword, or a expanded term definitions with an @id entry and optionally an @protected entry; no other entries are allowed. There is also an exception for aliases of @type, as indicated above. See § 4.1.11 Protected Term Definitions for further details of using @protected.
Since keywords cannot be redefined, they can also not be aliased to other keywords.
Note
Aliased keywords may not be used within a context, itself.
See § 9.16 Keywords for a normative definition of all keywords.
4.1.7 IRI Expansion within a Context
This section is non-normative.
In general, normal IRI expansion rules apply anywhere an IRI is expected (see § 3.2 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 values:
: IRI expansion within a 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.
Terms may also be used when defining the IRI of anotherterm:
: Using a term to define the IRI of another term within a context
{ "@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 aterm definition.
: Using a compact IRI as a term
{ "@context": { "foaf": "http://xmlns.com/foaf/0.1/", "xsd": "http://www.w3.org/2001/XMLSchema#", "name": "foaf:name", "foaf:age": { "@id": "http://xmlns.com/foaf/0.1/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 theIRI 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 full IRI forfoaf:homepage is determined by looking up the foaf prefix in thecontext.
Warning
If a compact IRI is used as a term, it must expand to the value that compact IRI would have on its own when expanded. This represents a change to the original 1.0 algorithm to prevent terms from expanding to a different IRI, which could lead to undesired results.
: Illegal Aliasing of a compact IRI to a different IRI
{ "@context": { "foaf": "http://xmlns.com/foaf/0.1/", "xsd": "http://www.w3.org/2001/XMLSchema#", "name": "foaf:name", "foaf:age": { "@id": "http://xmlns.com/foaf/0.1/age", "@type": "xsd:integer" }, "foaf:homepage": { "@id": "http://schema.org/url", "@type": "@id" } } }
IRIs may also be used in the key position in a context:
: Associating context definitions with IRIs
{ "@context": { "foaf": "http://xmlns.com/foaf/0.1/", "xsd": "http://www.w3.org/2001/XMLSchema#", "name": "foaf:name", "foaf:age": { "@id": "http://xmlns.com/foaf/0.1/age", "@type": "xsd:integer" }, "http://xmlns.com/foaf/0.1/homepage": { "@type": "@id" } } }
In order for the IRI to match above, the IRI needs to be used in the JSON-LD document. Also note that foaf:homepage will not use the { "@type": "@id" } declaration becausefoaf:homepage is not the same as http://xmlns.com/foaf/0.1/homepage. That is, terms are looked up in a context using direct string comparison before the prefix lookup mechanism is applied.
Warning
Neither an IRI reference nor a compact IRI may expand to some other unrelated IRI. This represents a change to the original 1.0 algorithm which allowed this behavior but discouraged it.
The only other exception for using terms in the context is that circular definitions are not allowed. That is, a definition of term1 cannot depend on the definition of term2 if term2 also depends on_term1_. For example, the following context definition is illegal:
: Illegal circular definition of terms within a context
{ "@context": { "term1": "term2:foo", "term2": "term1:bar" } }
4.1.8 Scoped Contexts
This section is non-normative.
An expanded term definition can include a @context property, which defines a context (a scoped context) forvalues of properties defined using that term. When used for a property, this is called a property-scoped context. This allows values to use term definitions, the base IRI,vocabulary mappings or the default language which are different from thenode object they are contained in, as if thecontext was specified within the value itself.
In this case, the social profile is defined using the schema.org vocabulary, but interest is imported from FOAF, and is used to define a node describing one of Manu's interests where those properties now come from the FOAF vocabulary.
Expanding this document, uses a combination of terms defined in the outer context, and those defined specifically for that term in a property-scoped context.
Scoping can also be performed using a term used as a value of @type:
Scoping on @type is useful when common properties are used to relate things of different types, where the vocabularies in use within different entities calls for different context scoping. For example,hasPart/partOf may be common terms used in a document, but mean different things depending on the context. A type-scoped context is only in effect for the node object on which the type is used; the previous in-scope contexts are placed back into effect when traversing into another node object. As described further in § 4.1.9 Context Propagation, this may be controlled using the @propagate keyword.
Note
Any property-scoped or local contexts that were introduced in the node object would still be in effect when traversing into another node object.
When expanding, each value of @type is considered (ordering them lexicographically) where that value is also a term in the active context having its own type-scoped context. If so, that the scoped context is applied to the active context.
Note
The values of @type are unordered, so if multiple types are listed, the order that type-scoped contexts are applied is based on lexicographical ordering.
For example, consider the following semantically equivalent examples. The first example, shows how properties and types can define their own scoped contexts, which are included when expanding.
: Expansion using embedded and scoped contexts
{
"@context": {
"@version": 1.1,
"@vocab": "http://example.com/vocab/",
"property": {
"@id": "http://example.com/vocab/property",
"@context": {
"term1": "http://example.com/vocab/term1"
↑ Scoped context for "property" defines term1
}
},
"Type1": {
"@id": "http://example.com/vocab/Type1",
"@context": {
"term3": "http://example.com/vocab/term3"
↑ Scoped context for "Type1" defines term3
}
},
"Type2": {
"@id": "http://example.com/vocab/Type2",
"@context": {
"term4": "http://example.com/vocab/term4"
↑ Scoped context for "Type2" defines term4
}
}
},
"property": {
"@context": {
"term2": "http://example.com/vocab/term2"
↑ Embedded context defines term2
},
"@type": ["Type2", "Type1"],
"term1": "a",
"term2": "b",
"term3": "c",
"term4": "d"
}
}Contexts are processed depending on how they are defined. A property-scoped context is processed first, followed by any embedded context, followed lastly by the type-scoped contexts, in the appropriate order. The previous example is logically equivalent to the following:
: Expansion using embedded and scoped contexts (embedding equivalent)
{
"@context": {
"@vocab": "http://example.com/vocab/",
"property": "http://example.com/vocab/property",
"Type1": "http://example.com/vocab/Type1",
"Type2": "http://example.com/vocab/Type2"
},
"property": {
"@context": [{
"term1": "http://example.com/vocab/term1"
↑ Previously scoped context for "property" defines term1
}, {
"term2": "http://example.com/vocab/term2"
↑ Embedded context defines term2
}, {
"term3": "http://example.com/vocab/term3"
↑ Previously scoped context for "Type1" defines term3
}, {
"term4": "http://example.com/vocab/term4"
↑ Previously scoped context for "Type2" defines term4
}],
"@type": ["Type2", "Type1"],
"term1": "a",
"term2": "b",
"term3": "c",
"term4": "d"
}
}Note
If a term defines a scoped context, and then that term is later redefined, the association of the context defined in the earlierexpanded term definition is lost within the scope of that redefinition. This is consistent withterm definitions of a term overriding previous term definitions from earlier less deeply nested definitions, as discussed in§ 4.1 Advanced Context Usage.
Note
Scoped Contexts are a new feature in JSON-LD 1.1.
4.1.9 Context Propagation
This section is non-normative.
Once introduced, contexts remain in effect until a subsequentcontext removes it by setting @context to null, or by redefining terms, with the exception of type-scoped contexts, which limit the effect of that context until the next node object is entered. This behavior can be changed using the @propagate keyword.
The following example illustrates how terms defined in a context with @propagate set to false are effectively removed when descending into new node object.
4.1.10 Imported Contexts
This section is non-normative.
JSON-LD 1.0 included mechanisms for modifying the context that is in effect. This included the capability to load and process a remotecontext and then apply further changes to it via new contexts.
However, with the introduction of JSON-LD 1.1, it is also desirable to be able to load a remote context, in particular an existing JSON-LD 1.0 context, and apply JSON-LD 1.1 features to it prior to processing.
By using the @import keyword in a context, another remotecontext, referred to as an imported context, can be loaded and modified prior to processing. The modifications are expressed in thecontext that includes the @import keyword, referred to as the wrapping context. Once an imported context is loaded, the contents of the wrapping context are merged into it prior to processing. The merge operation will cause each key-value pair in the wrapping context to be added to the loaded imported context, with the wrapping context key-value pairs taking precedence.
By enabling existing contexts to be reused and edited inline prior to processing, context-wide keywords can be applied to adjust all term definitions in the imported context. Similarly, term definitions can be replaced prior to processing, enabling adjustments that, for instance, ensure term definitions match previously protected terms or that they include additional type coercion information.
The following examples illustrate how @import can be used to express a type-scoped context that loads an imported context and sets @propagate to true, as a technique for making other similar modifications.
Suppose there was a context that could be referenced remotely via the URL https://json-ld.org/contexts/remote-context.jsonld:
: A remote context to be imported in a type-scoped context
{ "@context": { "Type1": "http://example.com/vocab/Type1", "Type2": "http://example.com/vocab/Type2", "term1": "http://example.com/vocab#term1", "term2": "http://example.com/vocab#term2" } }
A wrapping context could be used to source it and modify it:
: Sourcing a context in a type-scoped context and setting it to propagate
{ "@context": { "@version": 1.1, "MyType": { "@id": "http://example.com/vocab#MyType", "@context": { "@version": 1.1, "@import": "https://json-ld.org/contexts/remote-context.jsonld", "@propagate": true } } } }
The effect would be the same as if the entire imported context had been copied into the type-scoped context:
: Result of sourcing a context in a type-scoped context and setting it to propagate
{ "@context": { "@version": 1.1, "MyType": { "@id": "http://example.com/vocab#MyType", "@context": { "@version": 1.1, "Type1": "http://example.com/vocab/Type1", "Type2": "http://example.com/vocab/Type2", "term1": "http://example.com/vocab#term1", "term2": "http://example.com/vocab#term2", "@propagate": true } } } }
Similarly, the wrapping context may replace term definitions or set other context-wide keywords that may affect how the importedcontext term definitions will be processed:
: Sourcing a context to modify @vocab and a term definition
{ "@context": { "@version": 1.1, "@import": "https://json-ld.org/contexts/remote-context.jsonld", "@vocab": "http://example.org/vocab#",
"term1": {
"@id": "http://example.org/vocab#term1",
"@type": "http://www.w3.org/2001/XMLSchema#integer"
}} }
Again, the effect would be the same as if the entire imported context had been copied into the context:
: Result of sourcing a context to modify @vocab and a term definition
{ "@context": { "@version": 1.1, "Type1": "http://example.com/vocab/Type1", "Type2": "http://example.com/vocab/Type2", "term1": { "@id": "http://example.org/vocab#term1", "@type": "http://www.w3.org/2001/XMLSchema#integer" },
"term2": "http://example.com/vocab#term2",
"@vocab": "http://example.org/vocab#"} }
The result of loading imported contexts must becontext definition, not an IRI or an array. Additionally, the imported context cannot include an @import entry.
4.1.11 Protected Term Definitions
This section is non-normative.
JSON-LD is used in many specifications as the specified data format. However, there is also a desire to allow some JSON-LD contents to be processed as plain JSON, without using any of the JSON-LD algorithms. Because JSON-LD is very flexible, some terms from the original format may be locally overridden through the use of embedded contexts, and take a different meaning for JSON-LD based implementations. On the other hand, "plain JSON" implementations may not be able to interpret these embedded contexts, and hence will still interpret those terms with their original meaning. To prevent this divergence of interpretation, JSON-LD 1.1 allows term definitions to be protected.
A protected term definition is a term definition with an entry @protected set to true. It generally prevents further contexts from overriding this term definition, either through a new definition of the same term, or through clearing the context with "@context": null. Such attempts will raise an error and abort the processing (except in some specific situations describedbelow).
: A protected term definition can generally not be overridden
{
"@context": [
{
"@version": 1.1,
"Person": "http://xmlns.com/foaf/0.1/Person",
"knows": "http://xmlns.com/foaf/0.1/knows",
"name": {
"@id": "http://xmlns.com/foaf/0.1/name",
"@protected": true
}
},
{
– this attempt will fail with an error
"name": "http://schema.org/name"
}
],
"@type": "Person",
"name": "Manu Sporny",
"knows": {
"@context": [
– this attempt would also fail with an error
null,
"http://schema.org/"
],
"name": "Gregg Kellogg"
}
}When all or most term definitions of a context need to be protected, it is possible to add an entry @protected set to true to the context itself. It has the same effect as protecting each of its term definitions individually. Exceptions can be made by adding an entry @protected set to false in some term definitions.
While protected terms can in general not be overridden, there are two exceptions to this rule. The first exception is that a context is allowed to redefine a protected term if the new definition is identical to the protected term definition (modulo the @protected flag). The rationale is that the new definition does not violate the protection, as it does not change the semantics of the protected term. This is useful for widespread term definitions, such as aliasing @type to type, which may occur (including in a protected form) in several contexts.
The second exception is that a property-scoped context is not affected by protection, and can therefore override protected terms, either with a new term definition, or by clearing the context with "@context": null.
The rationale is that "plain JSON" implementations, relying on a given specification, will only traverse properties defined by that specification.Scoped contexts belonging to the specified properties are part of the specification, so the "plain JSON" implementations are expected to be aware of the change of semantics they induce.Scoped contexts belonging to other properties apply to parts of the document that "plain JSON" implementations will ignore. In both cases, there is therefore no risk of diverging interpretations between JSON-LD-aware implementations and "plain JSON" implementations, so overriding is permitted.
Note
By preventing terms from being overridden, protection also prevents any adaptation of a term (e.g., defining a more precise datatype, restricting the term's use to lists, etc.). This kind of adaptation is frequent with some general purpose contexts, for which protection would therefore hinder their usability. As a consequence, context publishers should use this feature with care.
Note
Protected term definitions are a new feature in JSON-LD 1.1.
4.2 Describing Values
This section is non-normative.
Values are leaf nodes in a graph associated with scalar values such asstrings, dates, times, and other such atomic values.
4.2.1 Typed Values
This section is non-normative.
A value with an associated type, also known as atyped 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 three ways:
- By utilizing the
@typekeyword when defining a term within an@contextsection. - By utilizing a value object.
- By using a native JSON type such as number,
true, orfalse.
The first example uses the @type keyword to associate a type with a particular term in the @context:
The modified key's value above is automatically interpreted as a_dateTime_ value because of the information specified in the@context. The example tabs show how a JSON-LD processor will interpret the data.
The second example uses the expanded form of setting the type information in the body of a JSON-LD document:
Both examples above would generate the value2010-05-29T14:17:39+02:00 with the typehttp://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 node. The concept of a node type and a value type are distinct. For more on adding types to nodes, see § 3.5 Specifying the Type.
Note
When expanding, an @type defined within a term definition can be associated with a string value to create an expanded value object, which is described in § 4.2.3 Type Coercion. Type coercion only takes place on string values, not for values which are maps, such as node objects and value objects in their expanded form.
A node type specifies the type of thing that is being described, like a person, place, event, or web page. Avalue type specifies the data type of a particular value, such as an integer, a floating point number, or a date.
: Example demonstrating the context-sensitivity for @type
{
"@id": "http://example.org/posts#TripToWestVirginia",
"@type": "http://schema.org/BlogPosting",
"http://purl.org/dc/terms/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 map, the @type keyword is expressing a value type. Otherwise, the @type keyword is expressing anode type. The example above expresses the following data:
4.2.2 JSON Literals
This section is non-normative.
At times, it is useful to include JSON within JSON-LD that is not interpreted as JSON-LD. Generally, a JSON-LD processor will ignore properties which don't map to IRIs, but this causes them to be excluded when performing various algorithmic transformations. But, when the data that is being described is, itself, JSON, it's important that it survives algorithmic transformations.
Warning
JSON-LD is intended to allow native JSON to be interpreted through the use of a context. The use of JSON literals creates blobs of data which are not available for interpretation. It is for use only in the rare cases that JSON cannot be represented as JSON-LD.
When a term is defined with @type set to @json, a JSON-LD processor will treat the value as a JSON literal, rather than interpreting it further as JSON-LD. In the expanded document form, such JSON will become the value of @value within a value object having "@type": "@json".
When transformed into RDF, the JSON literal will have a lexical form based on a specific serialization of the JSON, as described in Compaction algorithm of [JSON-LD11-API] and the JSON datatype.
The following example shows an example of a JSON Literal contained as the value of a property. Note that the RDF results use a canonicalized form of the JSON to ensure interoperability between different processors. JSON canonicalization is described in Data Round Tripping in [JSON-LD11-API].
Note
Generally, when a JSON-LD processor encounters null, the associated entry or value is removed. However, null is a valid JSON token; when used as the value of a JSON literal, a null value will be preserved.
4.2.3 Type Coercion
This section is non-normative.
JSON-LD supports the coercion of string values to particular data types. Type coercion allows someone deploying JSON-LD to use string property values and have those values be interpreted as typed valuesby associating an IRI with the value in the expanded value object representation. Using type coercion, string value representation can be used without requiring the data type to be specified explicitly with each piece of data.
Type coercion is specified within an expanded term definition using the @type key. The value of this key expands to an IRI. Alternatively, the keyword @id or @vocab may be used as value to indicate that within the body of a JSON-LD document, a string value of aterm coerced to @id or @vocab is to be interpreted as anIRI. The difference between @id and @vocab is how values are expanded to IRIs. @vocab first tries to expand the value by interpreting it as term. If no matching term is found in theactive context, it tries to expand it as an IRI or a compact IRI if there's a colon in the value; otherwise, it will expand the value using theactive context's vocabulary mapping, if present. Values coerced to @id in contrast are expanded as an IRI or a compact IRI if a colon is present; otherwise, they are interpreted as relative IRI references.
Note
The ability to coerce a value using a term definition is distinct from setting one or more types on a node object, as the former does not result in new data being added to the graph, while the latter manages node types through adding additional relationships to the graph.
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 aterm like xsd and then use xsd:integer within the same context definition.
The example below demonstrates how a JSON-LD author can coerce values totyped values and IRIs.
It is important to note that terms are only used in expansion for vocabulary-relative positions, such as for keys and values of map entries. Values of @id are considered to be document-relative, and do not use term definitions for expansion. For example, consider the following:
The unexpected result is that "barney" expands to both http://example1.com/barney and http://example2.com/barney, depending where it is encountered. String values interpreted as IRIs because of the associated term definitions are typically considered to be document-relative. In some cases, it makes sense to interpret these relative to the vocabulary, prescribed using "@type": "@vocab" in the term definition, though this can lead to unexpected consequences such as these.
In the previous example, "barney" appears twice, once as the value of @id, which is always interpreted as a document-relative IRI, and once as the value of "fred", which is defined to be vocabulary-relative, thus the different expanded values.
For more on this see § 4.1.2 Default Vocabulary.
A variation on the previous example using "@type": "@id" instead of @vocab illustrates the behavior of interpreting "barney" relative to the document:
Note
The triple ex1:fred ex2:knows ex1:barney . is emitted twice, but exists only once in an output dataset, as it is a duplicate triple.
Terms may also be defined using IRIs or compact IRIs. This allows coercion rules to be applied to keys which are not represented as a simple term. For example:
In this case the @id definition in the term definition is optional. If it does exist, the IRI or compact IRI representing the term will always be expanded to IRI defined by the @id key—regardless of whether a prefix is defined or not.
Type coercion is always performed using the unexpanded value of the key. In the example above, that means that type coercion is done looking for foaf:age in the active context and not for the corresponding, expandedIRI http://xmlns.com/foaf/0.1/age.
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.
4.2.4 String Internationalization
This section is non-normative.
At times, it is important to annotate a string with its language. In JSON-LD this is possible in a variety of ways. First, it is possible to define a default language for a JSON-LD document by setting the @language key in the context:
The example above would associate the ja language tag with the two strings 花澄 and 科学者 Languages tags are defined in [BCP47]. The default language applies to allstring values that are not type coerced.
To clear the default language for a subtree, @language can be set to null in an intervening context, such as a scoped context as follows:
: Clearing default language
{ "@context": {
"@version": 1.1,
"@vocab": "http://example.com/",
"@language": "ja",
"details": {
"@context": {
"@language": null
}
}}, "name": "花澄", "details": {"occupation": "Ninja"} }
Second, it is possible to associate a language with a specific term using an expanded term definition:
: Expanded term definition with language
{ "@context": {
"ex": "http://example.com/vocab/",
"@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 tag ja, Ninja with the language tagen, and Nindža with the language tag cs. The value of name, Yagyū Muneyoshi wouldn't be associated with any language tag since @language was reset tonull in the expanded term definition.
Note
Language associations are only applied to plainstrings. Typed values or values that are subject to type coercion are not language tagged.
Just as in the example above, systems often need to express the value of a property in multiple languages. Typically, such systems also try to ensure that developers have a programmatically easy way to navigate the data structures for the language-specific data. In this case, language maps may be utilized.
: Language map expressing a property in three languages
{ "@context": {
"occupation": { "@id": "ex:occupation", "@container": "@language" }}, "name": "Yagyū Muneyoshi", "occupation": { "ja": "忍者", "en": "Ninja", "cs": "Nindža" }
}
The example above expresses exactly the same information as the previous example but consolidates all values in a single property. To access the value in a specific language in a programming language supporting dot-notation accessors for object properties, a developer may use theproperty.language pattern (when languages are limited to the primary language sub-tag, and do not depend on other sub-tags, such as "en-us"). For example, to access the occupation in English, a developer would use the following code snippet:obj.occupation.en.
Third, it is possible to override the default language by using avalue object:
: Overriding default language using an expanded value
{ "@context": {
"@language": "ja"}, "name": "花澄", "occupation": { "@value": "Scientist", "@language": "en" } }
This makes it possible to specify a plain string by omitting the@language tag or setting it to null when expressing it using a value object:
: Removing language information using an expanded value
{ "@context": {
"@language": "ja"}, "name": { "@value": "Frank" }, "occupation": { "@value": "Ninja", "@language": "en" }, "speciality": "手裏剣" }
See § 9.8 Language Maps for a description of using language maps to set the language of mapped values.
4.2.4.1 Base Direction
This section is non-normative.
It is also possible to annotate a string, or language-tagged string, with its base direction. As with language, it is possible to define a default base direction for a JSON-LD document by setting the @direction key in the context:
The example above would associate the ar-EG language tag and "rtl" base direction with the two strings HTML و CSS: تصميم و إنشاء مواقع الويب and مكتبة. The default base direction applies to allstring values that are not type coerced.
To clear the default base direction for a subtree, @direction can be set to null in an intervening context, such as a scoped context as follows:
: Clearing default base direction
{ "@context": {
"@version": 1.1,
"@vocab": "http://example.com/",
"@language": "ar-EG",
"@direction": "rtl",
"details": {
"@context": {
"@direction": null
}
}}, "title": "HTML و CSS: تصميم و إنشاء مواقع الويب", "details": {"genre": "Technical Publication"} }
Second, it is possible to associate a base direction with a specific term using an expanded term definition:
: Expanded term definition with language and direction
{ "@context": {
"@version": 1.1,
"@language": "ar-EG",
"@direction": "rtl",
"ex": "http://example.com/vocab/",
"publisher": { "@id": "ex:publisher", "@direction": null },
"title": { "@id": "ex:title" },
"title_en": { "@id": "ex:title", "@language": "en", "@direction": "ltr" }}, "publisher": "مكتبة", "title": "HTML و CSS: تصميم و إنشاء مواقع الويب", "title_en": "HTML and CSS: Design and Build Websites" }
The example above would create three properties:
| Subject | Property | Value | Language | Direction |
|---|---|---|---|---|
| _:b0 | http://example.com/vocab/publisher | مكتبة | ar-EG | |
| _:b0 | http://example.com/vocab/title | HTML و CSS: تصميم و إنشاء مواقع الويب | ar-EG | rtl |
| _:b0 | http://example.com/vocab/title | HTML and CSS: Design and Build Websites | en | ltr |
Third, it is possible to override the default base direction by using avalue object:
: Overriding default language and default base direction using an expanded value
{ "@context": {
"@language": "ar-EG",
"@direction": "rtl"}, "title": "HTML و CSS: تصميم و إنشاء مواقع الويب", "author": { "@value": "Jon Duckett", "@language": "en", "@direction": null } }
See Strings on the Web: Language and Direction Metadata [string-meta] for a deeper discussion of base direction.
4.3 Value Ordering
This section is non-normative.
A JSON-LD author can express multiple values in a compact way by usingarrays. Since graphs do not describe ordering for links between nodes, arrays in JSON-LD do not convey any ordering of the 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:
Multiple values may also be expressed using the expanded form:
Note
The example shown above would generates statement, again with no inherent order.
Although multiple values of a property are typically of the same type, JSON-LD places no restriction on this, and a property may have values of different types:
Note
When viewed as statements, the values have no inherent order.
4.3.1 Lists
This section is non-normative.
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:
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:
The implementation of lists in RDF depends on linking anonymous nodes together using the properties rdf:first andrdf:rest, with the end of the list defined as the resourcerdf:nil, as the "statements" tab illustrates. This allows order to be represented within an unordered set of statements.
Both JSON-LD and Turtle provide shortcuts for representing ordered lists.
In JSON-LD 1.1, lists of lists, where the value of a list object, may itself be a list object, are fully supported.
Note that the "@container": "@list" definition recursively describes array values of lists as being, themselves, lists. For example, in The GeoJSON Format (see [RFC7946]),coordinates are an ordered list of positions, which are represented as an array of two or more numbers:
: Coordinates expressed in GeoJSON
{ "type": "Feature", "bbox": [-10.0, -10.0, 10.0, 10.0], "geometry": { "type": "Polygon", "coordinates": [ [ [-10.0, -10.0], [10.0, -10.0], [10.0, 10.0], [-10.0, -10.0] ] ] }
}
For these examples, it's important that values expressed within bbox and coordinates maintain their order, which requires the use of embedded list structures. In JSON-LD 1.1, we can express this using recursive lists, by simply adding the appropriate context definition:
Note that coordinates includes three levels of lists.
Values of terms associated with an @list container are always represented in the form of an array, even if there is just a single value or no value at all.
4.3.2 Sets
This section is non-normative.
While @list is used to describe ordered lists, the @set keyword is used to describe unordered sets. The use of @set in the body of a JSON-LD document is optimized away when processing the document, as it is just syntactic sugar. However, @set is helpful when used within the context of a document. Values of terms associated with an @set 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 compact form (see§ 5.2 Compacted Document Form). This makes post-processing of JSON-LD documents easier as the data is always in array form, even if the array only contains a single value.
This describes the use of this array as being unordered, and order may change when processing a document. By default, arrays of values are unordered, but this may be made explicit by setting @container to @set in the context:
Since JSON-LD 1.1, the @set keyword may be combined with other container specifications within an expanded term definition to similarly cause compacted values of indexes to be consistently represented using arrays. See § 4.6 Indexed Values for a further discussion.
4.3.3 Using @set with @type
This section is non-normative.
Unless the processing mode is set to json-ld-1.0,@type may be used with an expanded term definition with @container set to @set; no other entries may be set within such an expanded term definition. This is used by the Compaction algorithm to ensure that the values of @type (or an alias) are always represented in an array.
: Setting @container: @set on @type
{
"@context": {
"@version": 1.1,
"@type": {"@container": "@set"}
},
"@type": ["http:/example.org/type"]
}4.4 Nested Properties
This section is non-normative.
Many JSON APIs separate properties from their entities using an intermediate object; in JSON-LD these are called nested properties. For example, a set of possible labels may be grouped under a common property:
By defining labels using the keyword @nest, a JSON-LD processor will ignore the nesting created by using the_labels_ property and process the contents as if it were declared directly within containing object. In this case, the labels property is semantically meaningless. Defining it as equivalent to@nest causes it to be ignored when expanding, making it equivalent to the following:
Similarly, term definitions may contain a @nest property referencing a term aliased to @nest which will cause such properties to be nested under that aliased term when compacting. In the example below, both main_label and other_label are defined with "@nest": "labels", which will cause them to be serialized underlabels when compacting.
: Defining property nesting - Expanded Input
[{ "@id": "http://example.org/myresource", "http://xmlns.com/foaf/0.1/homepage": [ {"@id": "http://example.org"} ], "http://www.w3.org/2004/02/skos/core#prefLabel": [ {"@value": "This is the main label for my resource"} ], "http://www.w3.org/2004/02/skos/core#altLabel": [ {"@value": "This is the other label"} ] }]
: Defining property nesting - Context
{ "@context": { "@version": 1.1, "skos": "http://www.w3.org/2004/02/skos/core#", "labels": "@nest", "main_label": {"@id": "skos:prefLabel", "@nest": "labels"}, "other_label": {"@id": "skos:altLabel", "@nest": "labels"}, "homepage": {"@id": "http://xmlns.com/foaf/0.1/homepage", "@type": "@id"} } }
Note
Nested properties are a new feature in JSON-LD 1.1.
4.5 Embedding
This section is non-normative.
Embedding is a JSON-LD feature that allows an author to use node objects asproperty values. This is a commonly used mechanism for creating a parent-child relationship between two nodes.
Without embedding, node objects can be linked by referencing the identifier of another node object. For example:
The previous example describes two node objects, for Manu and Gregg, with the knows property defined to treat string values as identifiers.Embedding allows the node object for Gregg to be embedded as a value of the knows property:
A node object, like the one used above, may be used in any value position in the body of a JSON-LD document.
While it is considered a best practice to identify nodes in a graph, at times this is impractical. In the data model, nodes without an explicit identifier are called blank nodes, which can be represented in a serialization such as JSON-LD using a blank node identifier. In the previous example, the top-level node for Manu does not have an identifier, and does not need one to describe it within the data model. However, if we were to want to describe a knows relationship from Gregg to Manu, we would need to introduce a blank node identifier (here _:b0).
Blank node identifiers may be automatically introduced by algorithms such as flattening, but they are also useful for authors to describe such relationships directly.
4.5.1 Identifying Blank Nodes
This section is non-normative.
At times, it becomes necessary to be able to express information without being able to uniquely identify the node with an IRI. This type of node is called a blank node. JSON-LD does not require all nodes to be identified using @id. However, some graph topologies may require identifiers to be serializable. Graphs containing loops, e.g., cannot be serialized using embedding alone, @id must be used to connect the nodes. In these situations, one can use blank node identifiers, which look like IRIs using an underscore (_) as scheme. This allows one to reference the node locally within the document, but makes it impossible to reference the node from an external document. Theblank node identifier is scoped to the document in which it is used.
The example above contains information about two secret agents that cannot be identified with an IRI. While expressing that agent 1 knows agent 2 is possible without using blank node identifiers, it is necessary to assign agent 1 an identifier so that it can be referenced from agent 2.
It is worth noting that blank node identifiers may be relabeled during processing. If a developer finds that they refer to the blank node more than once, they should consider naming the node using a dereferenceable IRI so that it can also be referenced from other documents.
4.6 Indexed Values
This section is non-normative.
Sometimes multiple property values need to be accessed in a more direct fashion than iterating though multiple array values. JSON-LD provides an indexing mechanism to allow the use of an intermediate map to associate specific indexes with associated values.
Data Indexing
As described in § 4.6.1 Data Indexing, data indexing allows an arbitrary key to reference a node or value.
Language Indexing
As described in § 4.6.2 Language Indexing, language indexing allows a language to reference a string and be interpreted as the language associated with that string.
Node Identifier Indexing
As described in § 4.6.3 Node Identifier Indexing, node identifier indexing allows an IRI to reference a node and be interpreted as the identifier of that node.
Node Type Indexing
As described in § 4.6.4 Node Type Indexing, node type indexing allows an IRI to reference a node and be interpreted as a type of that node.
See § 4.9 Named Graphs for other uses of indexing in JSON-LD.
4.6.1 Data Indexing
This section is non-normative.
Databases are typically used to make access to data more efficient. Developers often extend this sort of functionality into their application data to deliver similar performance gains. This data may have no meaning from a Linked Data standpoint, but is still useful for an application.
JSON-LD introduces the notion of index maps that can be used to structure data into a form that is more efficient to access. The data indexing feature allows an author to structure data using a simple key-value map where the keys do not map to IRIs. This enables direct access to data instead of having to scan an array in search of a specific item. In JSON-LD such data can be specified by associating the@index keyword with a@container declaration in the context:
In the example above, the athletes term has been marked as an index map. The catcher and pitcher keys will be ignored semantically, but preserved syntactically, by the JSON-LD Processor. If used in JavaScript, this can allow a developer to access a particular athlete using the following code snippet: obj.athletes.pitcher.
The interpretation of the data is expressed in the statements table.Note how the index keys do not appear in the statements, but would continue to exist if the document were compacted or expanded (see § 5.2 Compacted Document Form and§ 5.1 Expanded Document Form) using a JSON-LD processor.
Warning
As data indexes are not preserved when round-tripping to RDF; this feature should be used judiciously. Often, other indexing mechanisms, which are preserved, are more appropriate.
The value of @container can also be an array containing both @index and @set. When compacting, this ensures that a JSON-LD Processor will use the array form for all values of indexes.
Unless the processing mode is set to json-ld-1.0, the special index @none is used for indexing data which does not have an associated index, which is useful to maintain a normalized representation.
4.6.1.1 Property-based data indexing
This section is non-normative.
In its simplest form (as in the examples above), data indexing assigns no semantics to the keys of an index map. However, in some situations, the keys used to index objects are semantically linked to these objects, and should be preserved not only syntactically, but also semantically.
Unless the processing mode is set to json-ld-1.0,"@container": "@index" in a term description can be accompanied with an "@index" key. The value of that key must map to an IRI, which identifies the semantic property linking each object to its key.
Note
When using property-based data indexing, index maps can only be used on node objects, not value objects or graph objects.Value objects are restricted to have only certain keys and do not support arbitrary properties.
4.6.2 Language Indexing
This section is non-normative.
JSON which includes string values in multiple languages may be represented using a language map to allow for easily indexing property values by language tag. This enables direct access to language values instead of having to scan an array in search of a specific item. In JSON-LD such data can be specified by associating the@language keyword with a@container declaration in the context:
In the example above, the label term has been marked as a language map. The en andde keys are implicitly associated with their respective values by the JSON-LD Processor. This allows a developer to access the German version of the label using the following code snippet: obj.label.de, which, again, is only appropriate when languages are limited to the primary language sub-tag and do not depend on other sub-tags, such as "de-at".
The value of @container can also be an array containing both @language and @set. When compacting, this ensures that a JSON-LD Processor will use the array form for all values of language tags.
Unless the processing mode is set to json-ld-1.0, the special index @none is used for indexing strings which do not have a language; this is useful to maintain a normalized representation for string values not having a datatype.
4.6.3 Node Identifier Indexing
This section is non-normative.
In addition to index maps, JSON-LD introduces the notion of id maps for structuring data. The id indexing feature allows an author to structure data using a simple key-value map where the keys map to IRIs. This enables direct access to associated node objects instead of having to scan an array in search of a specific item. In JSON-LD such data can be specified by associating the@id keyword with a@container declaration in the context:
In the example above, the post term has been marked as an id map. The http://example.com/posts/1/en andhttp://example.com/posts/1/de keys will be interpreted as the @id property of the node object value.
The interpretation of the data above is exactly the same as that in § 4.6.1 Data Indexing using a JSON-LD processor.
The value of @container can also be an array containing both @id and @set. When compacting, this ensures that a JSON-LD processor will use the array form for all values of node identifiers.
The special index @none is used for indexingnode objects which do not have an @id, which is useful to maintain a normalized representation. The @none index may also be a term which expands to @none, such as the term none used in the example below.
Note
Id maps are a new feature in JSON-LD 1.1.
4.6.4 Node Type Indexing
This section is non-normative.
In addition to id and index maps, JSON-LD introduces the notion of type maps for structuring data. The type indexing feature allows an author to structure data using a simple key-value map where the keys map to IRIs. This enables data to be structured based on the @type of specific node objects. In JSON-LD such data can be specified by associating the@type keyword with a@container declaration in the context:
In the example above, the affiliation term has been marked as a type map. The schema:Corporation andschema:ProfessionalService keys will be interpreted as the @type property of the node object value.
The value of @container can also be an array containing both @type and @set. When compacting, this ensures that a JSON-LD processor will use the array form for all values of types.
The special index @none is used for indexingnode objects which do not have an @type, which is useful to maintain a normalized representation. The @none index may also be a term which expands to @none, such as the term none used in the example below.
As with id maps, when used with @type, a container may also include @set to ensure that key values are always contained in an array.
Note
Type maps are a new feature in JSON-LD 1.1.
4.7 Included Nodes
This section is non-normative.
Sometimes it is also useful to list node objects as part of another node object. For instance, to represent a set of resources which are used by some other resource. Included blocks may be also be used to collect such secondary node objects which can be referenced from a primary node object. For an example, consider a node object containing a list of different items, some of which share some common elements:
: Included Blocks
{
"@context": {
"@version": 1.1,
"@vocab": "http://example.org/",
"classification": {"@type": "@vocab"}
},
"@id": "http://example.org/org-1",
"members": [{
"@id":"http://example.org/person-1",
"name": "Manu Sporny",
"classification": "employee"
}, {
"@id":"http://example.org/person-2",
"name": "Dave Longley",
"classification": "employee"
}, {
"@id": "http://example.org/person-3",
"name": "Gregg Kellogg",
"classification": "contractor"
}],
"@included": [{
"@id": "http://example.org/employee",
"label": "An Employee"
}, {
"@id": "http://example.org/contractor",
"label": "A Contractor"
}]
}When flattened, this will move the employee and contractor elements from the included block into the outer array.
Included resources are described inInclusion of Related Resources of JSON API [JSON.API] as a way to include related resources associated with some primary resource;@included provides an analogous possibility in JSON-LD.
As a by product of the use of @included within node objects, a map may contain only @included, to provide a feature similar to that described in § 4.1 Advanced Context Usage, where @graph is used to described disconnected nodes.
However, in contrast to @graph, @included does not interact with other properties contained within the same map, a feature discussed further in § 4.9 Named Graphs.
4.8 Reverse Properties
This section is non-normative.
JSON-LD serializes directed graphs. That means that every property points from a node to another node or value. However, in some cases, it is desirable to serialize in the reverse direction. Consider for example the case where a person and its children should be described in a document. If the used vocabulary does not provide a children property but just a parent property, every node representing a child would have to be expressed with a property pointing to the parent as in the following example.
Expressing such data is much simpler by using JSON-LD's @reverse keyword:
The @reverse keyword can also be used inexpanded term definitions to create reverse properties as shown in the following example:
4.9 Named Graphs
This section is non-normative.
At times, it is necessary to make statements about a graph itself, rather than just a single node. This can be done by grouping a set of nodes using the @graph keyword. A developer may also name data expressed using the@graph keyword by pairing it with an@id keyword as shown in the following example:
The example above expresses a named graph that is identified by the IRI http://example.org/foaf-graph. That graph is composed of the statements about Manu and Gregg. Metadata about the graph itself is expressed via the generatedAt property, which specifies when the graph was generated.
When a JSON-LD document's top-level structure is amap that contains no other keys than @graph and optionally @context (properties that are not mapped to anIRI or a keyword are ignored),@graph is considered to express the otherwise implicitdefault graph. This mechanism can be useful when a number of nodes exist at the document's top level that share the same context, which is, e.g., the case when a document is flattened. The@graph keyword collects such nodes in an array and allows the use of a shared context.
In this case, embedding can not be used as the graph contains unrelated nodes. This is equivalent to using multiplenode objects in array and defining the @context within each node object:
4.9.1 Graph Containers
This section is non-normative.
In some cases, it is useful to logically partition data into separate graphs, without making this explicit within the JSON expression. For example, a JSON document may contain data against which other metadata is asserted and it is useful to separate this data in the data model using the notion of named graphs, without the syntactic overhead associated with the @graph keyword.
An expanded term definition can use @graph as the value of @container. This indicates that values of thisterm should be considered to be named graphs, where thegraph name is an automatically assigned blank node identifier creating an implicitly named graph. When expanded, these becomesimple graph objects.
A different example uses an anonymously named graph as follows:
The example above expresses an anonymously named graph making a statement. The default graph includes a statement saying that the subject wrote that statement. This is an example of separating statements into a named graph, and then making assertions about the statements contained within that named graph.
Note
Graph Containers are a new feature in JSON-LD 1.1.
4.9.2 Named Graph Data Indexing
This section is non-normative.
In addition to indexing node objects by index, graph objects may also be indexed by an index. By using the @graph container type, introduced in § 4.9.1 Graph Containers in addition to @index, an object value of such a property is treated as a key-value map where the keys do not map to IRIs, but are taken from an @index property associated with named graphs which are their values. When expanded, these must be simple graph objects
The following example describes a default graph referencing multiple named graphs using an index map.
As with index maps, when used with @graph, a container may also include @set to ensure that key values are always contained in an array.
The special index @none is used for indexing graphs which do not have an @index key, which is useful to maintain a normalized representation. Note, however, that compacting a document where multiple unidentified named graphs are compacted using the @none index will result in the content of those graphs being merged. To prevent this, give each graph a distinct@index key.
Note
Named Graph Data Indexing is a new feature in JSON-LD 1.1.
4.9.3 Named Graph Indexing
This section is non-normative.
In addition to indexing node objects by identifier, graph objects may also be indexed by their graph name. By using the @graph container type, introduced in § 4.9.1 Graph Containers in addition to @id, an object value of such a property is treated as a key-value map where the keys represent the identifiers of named graphs which are their values.
The following example describes a default graph referencing multiple named graphs using an id map.
As with id maps, when used with @graph, a container may also include @set to ensure that key values are always contained in an array.
As with id maps, the special index @none is used for indexingnamed graphs which do not have an @id, which is useful to maintain a normalized representation. The @none index may also be a term which expands to @none.Note, however, that if multiple graphs are represented without an @id, they will be merged on expansion. To prevent this, use @none judiciously, and consider giving graphs their own distinct identifier.
Note
Graph Containers are a new feature in JSON-LD 1.1.
4.10 Loading Documents
This section is non-normative.
The JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API] defines the interface to a JSON-LD Processor and includes a number of methods used for manipulating different forms of JSON-LD (see § 5. Forms of JSON-LD). This includes a general mechanism for loading remote documents, including referenced JSON-LD documents and remote contexts, and potentially extracting embedded JSON-LD from other formats such as [HTML]. This is more fully described inRemote Document and Context Retrieval in [JSON-LD11-API].
A documentLoader can be useful in a number of contexts where loading remote documents can be problematic:
- Remote context documents should be cached to prevent overloading the location of the remote context for each request. Normally, an HTTP caching infrastructure might be expected to handle this, but in some contexts this might not be feasible. A documentLoader implementation might provide separate logic for performing such caching.
- Non-standard URL schemes may not be widely implemented, or may have behavior specific to a given application domain. A documentLoader can be defined to implement document retrieval semantics.
- Certain well-known contexts may be statically cached within a documentLoader implementation. This might be particularly useful in embedded applications, where it is not feasible, or even possible, to access remote documents.
- For security purposes, the act of remotely retrieving a document may provide a signal of application behavior. The judicious use of a documentLoader can isolate the application and reduce its online fingerprint.
5. Forms of JSON-LD
This section is non-normative.
As with many data formats, there is no single correct way to describe data in JSON-LD. However, as JSON-LD is used for describing graphs, certain transformations can be used to change the shape of the data, without changing its meaning as Linked Data.
Expanded Document Form
Expansion is the process of taking a JSON-LD document and applying acontext so that the @context is no longer necessary. This process is described further in § 5.1 Expanded Document Form.
Compacted Document Form
Compaction is the process of applying a provided context to an existing JSON-LD document. This process is described further in § 5.2 Compacted Document Form.
Flattened Document Form
Flattening is the process of extracting embedded nodes to the top level of the JSON tree, and replacing the embedded node with a reference, creating blank node identifiers as necessary. This process is described further in § 5.3 Flattened Document Form.
Framed Document Form
Framing is used to shape the data in a JSON-LD document, using an example frame document which is used to both match the flattened data and show an example of how the resulting data should be shaped. This process is described further in § 5.4 Framed Document Form.
5.1 Expanded Document Form
This section is non-normative.
The JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API] defines a method for expanding a JSON-LD document.Expansion is the process of taking a JSON-LD document and applying acontext 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:
: Sample JSON-LD document to be expanded
{
"@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/"
}Running the JSON-LD Expansion algorithm against the JSON-LD input document provided above would result in the following output:
JSON-LD's media type defines aprofile parameter which can be used to signal or requestexpanded document form. The profile URI identifyingexpanded document form is http://www.w3.org/ns/json-ld#expanded.
5.2 Compacted Document Form
This section is non-normative.
The JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API] defines a method for compacting a JSON-LD document. Compaction is the process of applying a developer-supplied context to shorten IRIs to terms or compact IRIs and JSON-LD values expressed in expanded form to simple values such asstrings or numbers. Often this makes it simpler to work with document as the data is expressed in application-specific terms. Compacted documents are also typically easier to read for humans.
For example, assume the following JSON-LD input document:
: Sample expanded JSON-LD document
[
{
"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:
: Sample context
{
"@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:
JSON-LD's media type defines aprofile parameter which can be used to signal or requestcompacted document form. The profile URI identifyingcompacted document form is http://www.w3.org/ns/json-ld#compacted.
The details of Compaction are described in theCompaction algorithm in [JSON-LD11-API]. This section provides a short description of how the algorithm operates as a guide to authors creating contexts to be used for compacting JSON-LD documents.
The purpose of compaction is to apply the term definitions, vocabulary mapping, default language, and base IRI to an existing JSON-LD document to cause it to be represented in a form that is tailored to the use of the JSON-LD document directly as JSON. This includes representing values as strings, rather than value objects, where possible, shortening the use of list objects into simple arrays, reversing the relationship between nodes, and using data maps to index into multiple values instead of representing them as an array of values.
5.2.1 Shortening IRIs
This section is non-normative.
In an expanded JSON-LD document, IRIs are always represented as absolute IRIs. In many cases, it is preferable to use a shorter version, either a relative IRI reference,compact IRI, or term. Compaction uses a combination of elements in a context to create a shorter form of these IRIs. See§ 4.1.2 Default Vocabulary,§ 4.1.3 Base IRI, and § 4.1.5 Compact IRIs for more details.
The vocabulary mapping can be used to shorten IRIs that may be vocabulary relative by removing the IRI prefix that matches the vocabulary mapping. This is done whenever an IRI is determined to be vocabulary relative, i.e., used as a property, or a value of @type, or as the value of a term described as "@type": "@vocab".
5.2.2 Representing Values as Strings
This section is non-normative.
To be unambiguous, the expanded document form always represents nodes and values using node objects and value objects. Moreover, property values are always contained within an array, even when there is only one value. Sometimes this is useful to maintain a uniformity of access, but most JSON data use the simplest possible representation, meaning thatproperties have single values, which are represented as strings or as structured values such as node objects. By default, compaction will represent values which are simple strings as strings, but sometimes a value is an IRI, a date, or some other typed value for which a simple string representation would loose information. By specifying this within a term definition, the semantics of a string value can be inferred from the definition of the term used as a property. See § 4.2 Describing Values for more details.
5.2.3 Representing Lists as Arrays
This section is non-normative.
As described in § 4.3.1 Lists, JSON-LD has an expanded syntax for representing ordered values, using the @list keyword. To simplify the representation in JSON-LD, a term can be defined with"@container": "@list" which causes all values of a property using such a term to be considered ordered.
5.2.4 Reversing Node Relationships
This section is non-normative.
In some cases, the property used to relate two nodes may be better expressed if the nodes have a reverse direction, for example, when describing a relationship between two people and a common parent. See § 4.8 Reverse Properties for more details.
Reverse properties can be even more useful when combined withframing, which can actually make node objects defined at the top-level of a document to become embedded nodes. JSON-LD provides a means to index such values, by defining an appropriate @container definition within a term definition.
5.2.5 Indexing Values
This section is non-normative.
Properties with multiple values are typically represented using an unordered array. This means that an application working on an internalized representation of that JSON would need to iterate through the values of the array to find a value matching a particular pattern, such as a language-tagged string using the language en.
Data can be indexed on a number of different keys, including @id, @type, @language, @index and more. See § 4.6 Indexed Values and§ 4.9 Named Graphs for more details.
5.2.6 Normalizing Values as Objects
This section is non-normative.
Sometimes it's useful to compact a document, but keep the node object and value object representations. For this, a term definition can set "@type": "@none". This causes the Value Compaction algorithm to always use the object form of values, although components of that value may be compacted.
5.2.7 Representing Singular Values as Arrays
This section is non-normative.
Generally, when compacting, properties having only one value are represented as strings or maps, while properties having multiple values are represented as an array of strings or maps. This means that applications accessing such properties need to be prepared to accept either representation. To force all values to be represented using an array, a term definition can set "@container": "@set". Moreover, @set can be used in combination with other container settings, for example looking at our language-map example from § 5.2.5 Indexing Values:
5.2.8 Term Selection
This section is non-normative.
When compacting, the Compaction algorithm will compact using a term for a property only when the values of that property match the@container, @type, and @language specifications for that term definition. This can actually split values between different properties, all of which have the same IRI. In case there is no matching term definition, the compaction algorithm will compact using the absolute IRI of the property.
5.3 Flattened Document Form
This section is non-normative.
The JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API] defines a method for flattening a JSON-LD document.Flattening collects all properties of a node in a single map and labels all blank nodes withblank node identifiers. This ensures a shape of the data and consequently may drastically simplify the code required to process JSON-LD in certain applications.
For example, assume the following JSON-LD input document:
: Sample JSON-LD document to be flattened
{
"@context": {
"name": "http://xmlns.com/foaf/0.1/name",
"knows": "http://xmlns.com/foaf/0.1/knows"
},
"@id": "http://me.markus-lanthaler.com/",
"name": "Markus Lanthaler",
"knows": [
{
"@id": "http://manu.sporny.org/about#manu",
"name": "Manu Sporny"
}, {
"name": "Dave Longley"
}
]
}Running the JSON-LD Flattening algorithm against the JSON-LD input document in the example above and using the same context would result in the following output:
JSON-LD's media type defines aprofile parameter which can be used to signal or requestflattened document form. The profile URI identifyingflattened document form is http://www.w3.org/ns/json-ld#flattened. It can be combined with the profile URI identifyingexpanded document form orcompacted document form.
5.4 Framed Document Form
This section is non-normative.
The JSON-LD 1.1 Framing specification [JSON-LD11-FRAMING] defines a method for framing a JSON-LD document. Framing is used to shape the data in a JSON-LD document, using an example frame document which is used to both match the flattened data and show an example of how the resulting data should be shaped.
For example, assume the following JSON-LD frame:
: Sample library frame
{
"@context": {
"@version": 1.1,
"@vocab": "http://example.org/"
},
"@type": "Library",
"contains": {
"@type": "Book",
"contains": {
"@type": "Chapter"
}
}
}This frame document describes an embedding structure that would place objects with type Library at the top, with objects of type Book that were linked to the library object using the contains property embedded as property values. It also places objects of type Chapter within the referencing Book object as embedded values of the Book object.
When using a flattened set of objects that match the frame components:
: Flattened library objects
{
"@context": {
"@vocab": "http://example.org/",
"contains": {"@type": "@id"}
},
"@graph": [{
"@id": "http://example.org/library",
"@type": "Library",
"contains": "http://example.org/library/the-republic"
}, {
"@id": "http://example.org/library/the-republic",
"@type": "Book",
"creator": "Plato",
"title": "The Republic",
"contains": "http://example.org/library/the-republic#introduction"
}, {
"@id": "http://example.org/library/the-republic#introduction",
"@type": "Chapter",
"description": "An introductory chapter on The Republic.",
"title": "The Introduction"
}]
}The Frame Algorithm can create a new document which follows the structure of the frame:
JSON-LD's media type defines aprofile parameter which can be used to signal or requestframed document form. The profile URI identifyingframed document form is http://www.w3.org/ns/json-ld#framed.
JSON-LD's media type also defines aprofile parameter which can be used to identify ascript element in an HTML document containing a frame. The first script element of type application/ld+json;profile=http://www.w3.org/ns/json-ld#frame will be used to find a frame..
6. Modifying Behavior with Link Relationships
Certain aspects of JSON-LD processing can be modified using [RFC8288]. These can be used when retrieving resources that are not, themselves, JSON-LD, but can be interpreted as JSON-LD by using information in aLink Relation.
When processing normal JSON documents, a link relation can be specified using the HTTP Link Header returned when fetching a remote document, as described in § 6.1 Interpreting JSON as JSON-LD.
In other cases, a resource may be returned using a representation that cannot easily be interpreted as JSON-LD. Normally, HTTP content negotiation would be used to allow a client to specify a preference for JSON-LD over another representation, but in certain situations, it is not possible or practical for a server to respond appropriately to such requests. For this, an HTTP Link Header can be used to provide an alternate location for a document to be used in place of the originally requested resource, as described in § 6.2 Alternate Document Location.
6.1 Interpreting JSON as JSON-LD
Ordinary JSON documents can be interpreted as JSON-LD by providing an explicit JSON-LD context document. One way to provide this is by using referencing a JSON-LDcontext document in an HTTP Link Header. Doing so allows JSON to be unambiguously machine-readable without requiring developers to drastically change their documents and provides an upgrade path for existing infrastructure without breaking existing clients that rely on the application/json media type or a media type with a +json suffix as defined in [RFC6839].
In order to use an external context with an ordinary JSON document, when retrieving an ordinary JSON document via HTTP, processors MUST attempt to retrieve any JSON-LD document referenced by aLink Header with:
rel="http://www.w3.org/ns/json-ld#context", andtype="application/ld+json".
The referenced document MUST have a top-level JSON object. The @context entry within that object is added to the top-levelJSON object of the referencing document. If an array is at the top-level of the referencing document and its items areJSON objects, 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. Effectively this means that the active context is initialized with the referenced external context. A response MUST NOT contain more than one HTTP Link Header using thehttp://www.w3.org/ns/json-ld#context link relation.
Other mechanisms for providing a JSON-LD Context MAY be described for other URI schemes.
The JSON-LD 1.1 Processing Algorithms and API specification [JSON-LD11-API] provides for an expandContext option for specifying a context to use when expanding JSON documents programmatically.
The following example demonstrates the use of an external context with an ordinary JSON document over HTTP:
Please note that 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. Contexts linked via ahttp://www.w3.org/ns/json-ld#context HTTP Link Header MUST be ignored for such documents.
6.2 Alternate Document Location
Documents which can't be directly interpreted as JSON-LD can provide an alternate location containing JSON-LD. One way to provide this is by referencing a JSON-LD document in an HTTP Link Header. This might be useful, for example, when the URL associated with a namespace naturally contains an HTML document, but the JSON-LD context associated with that URL is located elsewhere.
To specify an alternate location, a non-JSON resource (i.e., one using a media type other than application/json or a derivative) can return the alternate location using a Link Header with:
rel="alternate", andtype="application/ld+json".
A response MUST NOT contain more than one HTTP Link Header using thealternate link relation with type="application/ld+json" .
Other mechanisms for providing an alternate location MAY be described for other URI schemes.
The following example demonstrates the use of an alternate location with an ordinary HTTP document over HTTP:
A processor seeing a non-JSON result will note the presence of the link header and load that document instead.
7. Embedding JSON-LD in HTML Documents
JSON-LD content can be easily embedded in HTML [HTML] by placing it in a script element with the type attribute set toapplication/ld+json. Doing so creates adata block.
Defining how such data may be used is beyond the scope of this specification. The embedded JSON-LD document might be extracted as is or, e.g., be interpreted as RDF.
If JSON-LD content is extracted as RDF [RDF11-CONCEPTS], it MUST be expanded into anRDF Dataset using theDeserialize JSON-LD to RDF Algorithm [JSON-LD11-API]. Unless a specific script is targeted (see § 7.3 Locating a Specific JSON-LD Script Element), all script elements with type application/ld+json MUST be processed and merged into a single dataset with equivalent blank node identifiers contained in separate script elements treated as if they were in a single document (i.e., blank nodes are shared between different JSON-LD script elements).
7.1 Inheriting base IRI from HTML's base element
When processing a JSON-LDscript element, the Document Base URL of the containing HTML document, as defined in [HTML], is used to establish the default base IRI of the enclosed JSON-LD content.
HTML allows for Dynamic changes to base URLs. This specification does not require any specific behavior, and to ensure that all systems process the base IRI equivalently, authors SHOULD either use IRIs, or explicitly as defined in § 4.1.3 Base IRI. Implementations (particularly those natively operating in the [DOM]) MAY take into considerationDynamic changes to base URLs.
7.2 Restrictions for contents of JSON-LD script elements
This section is non-normative.
Due to the HTML Restrictions for contents of