JSON-LD Syntax 1.0

6.1 Compact IRIs

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

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

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

{
  "@context":
  {
    "foaf": "http://xmlns.com/foaf/0.1/"
...
  },
  "foaf:name": "Dave Longley",
...
}

foaf:name above will automatically expand out to the IRI http://xmlns.com/foaf/0.1/name .

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

Consider the following example:

{
  "@context":

  {
    
    

    "dc": "http://purl.org/dc/elements/1.1/",
    "ex": "http://example.org/vocab#"
  },
  "@id": "http://example.org/library",
  "@type": ,
  :

  "@id": "http://example.org/library",
  "@type": "ex:Library",
  "ex:contains":
  {
    "@id": "http://example.org/library/the-republic",
    "@type": ,
    : "Plato",
    : "The Republic",
    :

    "@id": "http://example.org/library/the-republic",
    "@type": "ex:Book",
    "dc:creator": "Plato",    "dc:title": "The Republic",    "ex:contains":
    {
      "@id": "http://example.org/library/the-republic#introduction",
      "@type": ,
      : "An introductory chapter on The Republic.",
      : "The Introduction"

      "@id": "http://example.org/library/the-republic#introduction",
      "@type": "ex:Chapter",
      "dc:description": "An introductory chapter on The Republic.",      "dc:title": "The Introduction"
    }
  }
}

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

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

{
  "@context":

  {
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "foaf": "http://xmlns.com/foaf/0.1/",
    : { "@type": "@id" },
    "picture": { "@id": , "@type": "@id" }

    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "foaf": "http://xmlns.com/foaf/0.1/",    "foaf:homepage": { "@type": "@id" },
    "picture": { "@id": "foaf:depiction", "@type": "@id" }

  },
  "@id": "http://me.markus-lanthaler.com/",
  "@type": "foaf:Person",
  "foaf:name": "Markus Lanthaler",
  "foaf:homepage": "http://www.markus-lanthaler.com/",
  "picture": "http://twitter.com/account/profile_image/markuslanthaler"

  "@id": "http://me.markus-lanthaler.com/",
  "@type": "foaf:Person",
  "foaf:name": "Markus Lanthaler",
  "foaf:homepage": "http://www.markus-lanthaler.com/",
  "picture": "http://twitter.com/account/profile_image/markuslanthaler"

}

6.2 Typed Values

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

1. By utilizing the @type keyword when defining a term within a @context section.
2. By utilizing an expanded typed value .
3. By using a native JSON type such as number , true , or false .

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

{
  "@context":
  {
    "modified":

    "modified":

    {
      "@id": "http://purl.org/dc/terms/modified",
      "@type": "http://www.w3.org/2001/XMLSchema#dateTime"

      "@id": "http://purl.org/dc/terms/modified",
      "@type": "http://www.w3.org/2001/XMLSchema#dateTime"

    }
  },
...
  "modified": "2010-05-29T14:17:39+02:00",

  "@id": "http://example.com/docs/1",
  "modified": "2010-05-29T14:17:39+02:00",

...
}

The modified key's value above is automatically type coerced to a datetime dateTime value because of the information specified in the @context . A JSON-LD processor will interpret the markup above like so:

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

{
  "@context":

  {
    "modified":

    "modified":

    {
      "@id": "http://purl.org/dc/terms/modified"

      "@id": "http://purl.org/dc/terms/modified"

    }
  },
...
  "modified":

  "modified":

  {
    "@value": "2010-05-29T14:17:39+02:00",
    "@type": "http://www.w3.org/2001/XMLSchema#dateTime"

    "@value": "2010-05-29T14:17:39+02:00",
    "@type": "http://www.w3.org/2001/XMLSchema#dateTime"

  }
...
}

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

The @type keyword is also used to associate a type with a node . The concept of a node type and a value type are different. This

Generally speaking, a node type specifies the type of thing that is similar to object-oriented programming languages where both scalar and structured types use being described, like a person, place, event, or web page. A value type specifies the same class inheritance mechanism, even though scalar types and structured types are inherently different. unit of measurement for a particular value, such as a date, meter, or light year.

{
...
  "@id": "http://example.org/posts#TripToWestVirginia",
  ,
  "modified":

  "@id": "http://example.org/posts#TripToWestVirginia",
  "@type": "http://schema.org/BlogPosting",   <--- This is a node type
  "modified":

  {
    "@value": "2010-05-29T14:17:39+02:00",
    

    "@value": "2010-05-29T14:17:39+02:00",
    "@type": "http://www.w3.org/2001/XMLSchema#dateTime" <--- This is a value type
  }
...
}

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

6.3 Language-tagged Strings Type Coercion

A string with an associated language, also known as a language-tagged string , is indicated by associating a string with JSON-LD supports the coercion of values to particular data types. Type coercion allows someone deploying JSON-LD to coerce the incoming or outgoing values to the proper data type based on a language code as defined in [ BCP47 mapping of data type IRIs ]. Language-tagged strings may to terms . Using type coercion, value representation is preserved without requiring the data type to be expressed in JSON-LD in four ways: specified with each piece of data.

Type coercion is specified within an expanded term definition using the @language @type key. The value of this key expands to an IRI . Alternatively, the keyword within a @context @id section. By utilizing may be used as value to indicate that within the @language keyword when defining body of a JSON-LD document, a string value of a term within a coerced to @context @id section. By utilizing is to be interpreted as an expanded language-tagged string IRI . By utilizing a language map , provided

Terms or compact IRIs used as the underlying value of a term @type is key may be defined with within the same context. This means that one may specify a @container keyword term whose value is like @language xsd within a and then use @context xsd:integer section. within the same context definition.

The first example uses the @language keyword to associate a type with below demonstrates how a particular term in the @context : JSON-LD author can coerce values to typed values , IRIs, and lists.

{
  "@context":

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

    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "http://xmlns.com/foaf/0.1/name",
    "age":
    {
      "@id": "http://xmlns.com/foaf/0.1/age",
      "@type": "xsd:integer"
    },
    "homepage":
    {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id",
      "@container": "@list"
    }
  },
  "@id": "http://example.com/people#john",
  "name": "John Smith",
  "age": "41",
  "homepage":
  [
    "http://personal.example.org/",
    "http://work.example.com/jsmith/"
  ]

}

The modified key's value markup shown above is automatically language coerced to a English value because of the information specified in would generate the @context . following data. The second example uses data has no inherent order except for the expanded form values of setting the language information in the body of http://schema.org/homepage property which represent an ordered list.

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

{
  "@context":

  {
    "title":

    "foaf": "http://xmlns.com/foaf/0.1/",
    "foaf:age":

    {
      "@id": "http://purl.org/dc/terms/title"

      "@id": "http://xmlns.com/foaf/0.1/age",
      "@type": "xsd:integer"
    },
    "http://xmlns.com/foaf/0.1/homepage":
    {
      "@type": "@id"

    }
  },
...
  "title":
  {
    "@value": "JSON-LD Syntax",
    "@language": "en"
  }
...

  "foaf:name": "John Smith",
  "foaf:age": "41",
  "http://xmlns.com/foaf/0.1/homepage":
  [
    "http://personal.example.org/",
    "http://work.example.com/jsmith/"
  ]

}

Both examples above would generate In this case the value JSON-LD Syntax @id tagged with definition in the language en ; which term definition is optional, but if it does exist, the [ compact IRI BCP47 or ] code IRI is treated as a term (not a prefix:suffix construct) so that the actual definition of a prefix becomes unnecessary. Type coercion is performed using the unexpanded value of the key if there is an exact match for the English language. key in the active context .

6.4 Advanced Context Usage

Section 5.1 The Context introduced the language-specific data. In this case, language maps basics of what makes JSON-LD work. This section expands on the basic principles of the context and demonstrates how more advanced use cases can be achieved using JSON-LD.

In general, contexts may be utilized. used at any time a JSON object is defined. The only time that one cannot express a context is inside a context definition itself. For example, a JSON-LD document may use more than one context at different points in a document:

[
  {
    "title":
    {
      "@id": "http://purl.org/dc/terms/title",
      
    }

    "@context": "http://example.org/contexts/person.jsonld",
    "name": "Manu Sporny",
    "homepage": "http://manu.sporny.org/",
    "depiction": "http://twitter.com/account/profile_image/manusporny"

  },
...
  "title":
  {
    "en": "JSON-LD Syntax",
    "ru": "JSON-LD Синтаксис",
    "ja": "JSON-LDの構文"
  }
...

  {
    "@context": "http://example.org/contexts/place.jsonld",
    "name": "The Empire State Building",
    "description": "The Empire State Building is a 102-story landmark in New York City.",
    "geo": {
      "latitude": "40.75",
      "longitude": "73.98"
    }
  }
]

Duplicate context terms are overridden using a last-defined-wins mechanism.

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

}

In the example above, the title name term is expressed overridden in three languages; English, Russian, the more deeply nested details structure. Note that this is rarely a good authoring practice and Japanese. To access is typically used when working with legacy applications that depend on a specific structure of the data above JSON object . 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 of terms 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 programming language supporting dot-notation accessors for specific JSON object properties, are referred to as local contexts . The active context refers to the accumulation of local contexts that are in scope at a developer may use specific point within the document. Setting a local context to property.language null pattern. For example, effectively resets the active context to access an empty context. The following example specifies an external context and then layers an embedded context on top of the Japanese version external context:

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

GET /ordinary-json-document.json HTTP/1.1
Host: example.com
Accept: application/ld+json,application/json,*/*;q=0.1
====================================
HTTP/1.0 200 OK
...
Content-Type: application/json
Link: <http://json-ld.org/contexts/person.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"
{
  "name": "Markus Lanthaler",
  "homepage": "http://www.markus-lanthaler.com/",
  "depiction": "http://twitter.com/account/profile_image/markuslanthaler"

  "name": "Markus Lanthaler",
  "homepage": "http://www.markus-lanthaler.com/",
  "image": "http://twitter.com/account/profile_image/markuslanthaler"

}

6.5 Expanded Term Definition String Internationalization

Within At times, it is important to annotate a context definition, terms may be defined using an expanded term definition string with its language. In JSON-LD this is possible in a variety of ways. First, it is possible to allow define a default language for additional information associated with a JSON-LD document by setting the term to be specified (see also 6.6 Type Coercion @language key in the context :

{  "@context":
  {
    ...
    "@language": "ja"
  },
  "name": "花澄",
  "occupation": "科学者"
}

The example above would associate the ja language code with the two strings 花澄 and 6.9 Sets and Lists 科学者 . Languages codes are defined in [ BCP47 ). ].

Instead of using a string representation of an IRI , To clear the IRI may be specified using default language for a JSON object having an subtree, @id @language key, and a term , can be set to null in a compact IRI , or an absolute IRI local context as value. follows:

{
  "@context": {
    ...
    "@language": "ja"

  },
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "depiction": "http://twitter.com/account/profile_image/manusporny"

  "name": "花澄",
  "details": {
    "@context": {
      "@language": null
    },
    "occupation": "Ninja"
  }

}

This allows additional information to be associated with the term. This may be used for 6.6 Type Coercion , 6.9 Sets and Lists , or Second, it is possible to associate a language information with a specific term as shown in the following example: using an expanded term definition :

{
  "@context": {

    ...
    "ex": "http://example.com/",
    "@language": "ja",
    "name": { "@id": "ex:name",  },
    "occupation": { "@id": "ex:occupation" },
    "occupation_en": { "@id": "ex:occupation",  },
    "occupation_cs": { "@id": "ex:occupation",  }

    "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",

  "name": "Yagyū Muneyoshi",
  "occupation": "忍者",
  "occupation_en": "Ninja",
  "occupation_cs": "Nindža",

  ...
}

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

Just as value in the example above, systems often need to indicate that within express the body of a JSON-LD document, a string value of a term coerced property in multiple languages. Typically, such systems also try to @id is 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 interpreted as an IRI . utilized.

{
  "@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 of in a @type key specific language in a programming language supporting dot-notation accessors for object properties, a developer may be defined within use the same context. This means that one may specify a term like xsd property.language and then pattern. For example, to access the occupation in English, a developer would use xsd:integer within the same context definition. following code snippet: obj.occupation.en .

The example below demonstrates how a JSON-LD author can coerce values Third, it is possible to typed values , IRIs and lists. override the default language by using an expanded value :

{
  "@context": {
    ...
    "@language": "ja"

  },
  "@id": "http://example.com/people#john",
  "name": "John Smith",
  "age": ,
  "homepage":
  [
    "http://personal.example.org/",
    "http://work.example.com/jsmith/"
  ]

  "name": "花澄",
  "occupation": {
    "@value": "Scientist",
    "@language": "en"
  }

}

The markup shown above would generate the following data. The data has no inherent order except for the values This makes it possible to specify a plain string by omitting the http://xmlns.com/foaf/0.1/homepage @language property which represent an ordered list. Subject Property Object Datatype http://example.com/people#john http://xmlns.com/foaf/0.1/name John Smith http://example.com/people#john http://xmlns.com/foaf/0.1/age 41 http://www.w3.org/2001/XMLSchema#integer http://example.com/people#john http://xmlns.com/foaf/0.1/homepage http://personal.example.org/ http://work.example.com/jsmith/ Terms may also be defined using absolute IRIs tag or compact IRIs . This allows coercion rules to be applied setting it to keys which are not represented as a simple term . For example: null when expressing it using an expanded value :

{
  "@context": {
    ...
    "@language": "ja"

  },
  "foaf:name": "John Smith",
  "": "41",
  "":
  [
    "http://personal.example.org/",
    "http://work.example.com/jsmith/"
  ]

  "name": {
    "@value": "Frank"
  },
  "occupation": {
    "@value": "Ninja",
    "@language": "en"
  },
  "speciality": "手裏剣"

}

6.6 Overriding @vocab

In this case the If @id @vocab definition in the term definition is optional, used but if it does exist, the compact IRI certain keys in an object or should not be expanded using the vocabulary IRI is treated as , a term (not a prefix:suffix construct) so that the actual definition of a prefix becomes unnecessary. Type coercion is performed using the unexpanded value of the key, which has can be explicitly set to match exactly an entry null in the active context . Note Keys For instance, in the context are treated as terms for the purpose of expansion and value coercion. At times, this may result in multiple representations for example below the same expanded IRI . For example, one could specify that dog and cat databaseId both expanded to http://example.com/vocab#animal . Doing this could member would be useful for establishing different type coercion or language specification rules. It also allows ignored by a compact IRI (or even an absolute JSON-LD processor.

) to be defined as something else entirely. For example, one could specify that the term http://example.org/zoo should expand to http://example.org/river , but this usage is discouraged because it would lead to a great deal of confusion among developers attempting to understand the JSON-LD document.

{
  "@context":
  {
     "@vocab": "http://schema.org/",
     "databaseId": null
  },
  "name": "Gregg Kellogg",
  "databaseId": "23987520"
}

6.7 Property Generators

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

{
  "@context":

  {
    ,
    ,
    

    "title1": "http://purl.org/dc/terms/title",
    "title2": "http://schema.org/name",
    "title3": "http://www.w3.org/2000/01/rdf-schema#label"
  },
  "@id": "http://example.com/book",
  ,
  ,
  

  "@id": "http://example.com/book",
  "title1": "The Count of Monte Cristo",  "title2": "The Count of Monte Cristo",  "title3": "The Count of Monte Cristo"
}

Unfortunately, the approach above produces redundant data and would become a publishing burden for large data sets. In these situations, the author may use a property generator to express a term that maps to multiple properties in the JSON-LD graph . This method can be accomplished by using the following markup pattern:

{
  "@context":

  {
    "title": { "@id": [ "http://purl.org/dc/terms/title",
                        "http://schema.org/name",
                        "http://www.w3.org/2000/01/rdf-schema#label" ] }

    "title": { "@id": [ "http://purl.org/dc/terms/title",
                        "http://schema.org/name",
                        "http://www.w3.org/2000/01/rdf-schema#label" ] }

  },
  "@id": "http://example.com/book",
  

  "@id": "http://example.com/book",
  "title": "The Count of Monte Cristo"
}

While the term above is only used once outside of the @context , the document above is equivalent to the following: will be interpreted like so:

6.8 IRI Expansion Within a Context

In general, normal IRI expansion rules apply anywhere an IRI is expected (see 5.3 5.2 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 value s:

{
  "@context":

  {
    ,
    "name": "http://xmlns.com/foaf/0.1/name",
    "age":

    "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": 

      "@id": "http://xmlns.com/foaf/0.1/age",
      "@type": "xsd:integer"

    },
    "homepage":

    "homepage":

    {
      "@id": "http://xmlns.com/foaf/0.1/homepage",
      "@type": "@id"

      "@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 another term :

{
  "@context":

  {
    ,
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": ,
    "age":

    "foaf": "http://xmlns.com/foaf/0.1/",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "foaf:name",
    "age":

    {
      "@id": ,
      "@type": "xsd:integer"

      "@id": "foaf:age",
      "@type": "xsd:integer"

    },
    "homepage":

    "homepage":

    {
      "@id": ,
      "@type": "@id"

      "@id": "foaf:homepage",
      "@type": "@id"

    }
  },
  ...
}

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

{
  "@context":

  {
    ,
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "foaf:name",
    "":

    "foaf": "http://xmlns.com/foaf/0.1/",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "foaf:name",
    "foaf:age":

    {
      "@type": "xsd:integer"

      "@type": "xsd:integer"

    },
    "":

    "foaf:homepage":

    {
      "@type": "@id"

      "@type": "@id"

    }
  },
  ...
}

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

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

{
  "@context":

  {
    "foaf": "http://xmlns.com/foaf/0.1/",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "foaf:name",
    "foaf:age":

    "foaf": "http://xmlns.com/foaf/0.1/",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "name": "foaf:name",
    "foaf:age":

    {
      "@id": "foaf:age",
      "@type": "xsd:integer"

      "@id": "foaf:age",
      "@type": "xsd:integer"

    },
    "":

    "http://xmlns.com/foaf/0.1/homepage":

    {
      "@type": "@id"

      "@type": "@id"

    }
  },
  ...
}

In order for the absolute IRI to match above, the absolute IRI needs to be used in the JSON-LD document . Also note that foaf:homepage will not use the { "@type": "@id" "@type": "@id" } declaration because foaf: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.

The only exception for using terms in the context is that circular definitions are not allowed. That is, a definition of term-1 term1 cannot depend on the definition of term-2 term2 if term-2 term2 also depends on term-1 term1 . For example, the following context definition is illegal:

{
  "@context":

  {
    "term1": "term2:foo",
    "term2": "term1:bar"

    "term1": "term2:foo",
    "term2": "term1:bar"

  },
  ...
}

6.9 Sets and Lists

A JSON-LD author can express multiple values in a compact way by using arrays . Since graphs do not describe ordering for links between nodes, arrays in JSON-LD do not provide an 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:

{
...
  "@id": "http://example.org/people#joebob",
  "nick": ,

  "@id": "http://example.org/people#joebob",
  "nick": [ "joe", "bob", "JB" ],

...
}

The markup shown above would result in the following data being generated, each relating the node to an individual value, with no inherent order:

Multiple values may also be expressed using the expanded form:

{
  "@id": "http://example.org/articles/8",
  "dc:title": 

  [
    {
      "@value": "Das Kapital",
      "@language": "de"

      "@value": "Das Kapital",
      "@language": "de"

    },
    {
      "@value": "Capital",
      "@language": "en"

      "@value": "Capital",
      "@language": "en"

    }
  ]
}

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

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:

{
...
  "@id": "http://example.org/people#joebob",
  "foaf:nick":

  "@id": "http://example.org/people#joebob",
  "foaf:nick":

  {
    "@list": [ "joe", "bob", "jaybee" ]

    "@list": [ "joe", "bob", "jaybee" ]

  },
...
}

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

{
  "@context":
  {
    ...
    "nick":

    "nick":

    {
      "@id": "http://xmlns.com/foaf/0.1/nick",
      "@container": "@list"

      "@id": "http://xmlns.com/foaf/0.1/nick",
      "@container": "@list"

    }
  },
...
  "@id": "http://example.org/people#joebob",
  "nick": ,

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

...
}

Similarly to While @list , there exists is used to describe ordered sets , the keyword @set keyword is used to describe unordered sets. While its sets . The use of @set in the body of a JSON-LD document represents just syntactic sugar is optimized away when processing the document, as it is very just syntactic sugar. However, @set is helpful when used within the context of a document. Values of terms associated with a @set or @list container are always represented in the form of an array - , even if there is just a single value that would otherwise be optimized to a non-array form in a compact form (see 6.17 6.15 Compact Document Form . ). This makes post-processing of the data JSON-LD documents easier as the data is always in array form, even if the array only contains a single value.

6.10 Embedding

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

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

{
...
  "name": "Manu Sporny",
  "":

  "name": "Manu Sporny",
  "knows":

  {
    "",
    "",

    "@type": "Person",
    "name": "Gregg Kellogg",

  }
...
}

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

6.11 Named Graphs

At times, it is necessary to make statements about a JSON-LD 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:

{
  "@context": {
    "generatedAt": "http://www.w3.org/ns/prov#generatedAtTime",
    "Person": "http://xmlns.com/foaf/0.1/Person",
    "name": "http://xmlns.com/foaf/0.1/name",
    "knows": "http://xmlns.com/foaf/0.1/knows",
    "xsd": "http://www.w3.org/2001/XMLSchema#"

  },
  "@id": "http://example.org/graphs/73",
  "generatedAt": { "@value": "2012-04-09", "@type": "xsd:date" },
  "@graph":

  "@id": "http://example.org/graphs/73",
  "generatedAt": { "@value": "2012-04-09", "@type": "xsd:date" },
  "@graph":

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

      "@id": "http://manu.sporny.org/i/public",
      "@type": "Person",
      "name": "Manu Sporny",
      "knows": "http://greggkellogg.net/foaf#me"

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

      "@id": "http://greggkellogg.net/foaf#me",
      "@type": "Person",
      "name": "Gregg Kellogg",
      "knows": "http://manu.sporny.org/i/public"

    }
  ]
}

The example above expresses a named JSON-LD graph that is identified by the IRI http://example.org/graphs/73 . That graph is composed of the statements about Manu and Gregg. Metadata about the graph itself is also expressed via the generatedAt property, which specifies when the graph was generated. An alternative view of the information above is represented in table form below:

When @graph is used in a document's top-level object which has no other properties that are mapped to an IRI or a keyword it is considered to express the otherwise implicit default graph. This mechanism can be useful when a number of nodes thay may do not directly relate to one another through a property or where embedding is not desirable to the application. For example:

{
  "@context": ...,
  "@graph":

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

      "@id": "http://manu.sporny.org/i/public",
      "@type": "foaf:Person",
      "name": "Manu Sporny",
      "knows": "http://greggkellogg.net/foaf#me"

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

      "@id": "http://greggkellogg.net/foaf#me",
      "@type": "foaf:Person",
      "name": "Gregg Kellogg",
      "knows": "http://manu.sporny.org/i/public"

    }
  ]
}

In this case, embedding doesn't work as each node object references the other. Using the @graph keyword allows multiple nodes to be defined within an array , and allows the use of a shared context . This is equivalent to using multiple node objects in array and defining the @context within each node object :

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

    "@context": ...,
    "@id": "http://manu.sporny.org/i/public",
    "@type": "foaf:Person",
    "name": "Manu Sporny",
    "knows": "http://greggkellogg.net/foaf#me"

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

    "@context": ...,
    "@id": "http://greggkellogg.net/foaf#me",
    "@type": "foaf:Person",
    "name": "Gregg Kellogg",
    "knows": "http://manu.sporny.org/i/public"

  }
]

6.12 Identifying Blank Nodes

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

{
...
  "@id": "",

  "@id": "_:foo",

...
}

The example above would set the node to _:foo , which can then be used elsewhere in the JSON-LD document to refer back to the blank node . 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.

6.13 Aliasing Keywords

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

{
  "@context":

  {
     ,
     ,
     "name": "http://schema.org/name"

     "url": "@id",
     "a": "@type",
     "name": "http://xmlns.com/foaf/0.1/name"

  },
  "": "http://example.com/about#gregg",
  "": "http://schema.org/Person",
  "name": "Gregg Kellogg"

  "url": "http://example.com/about#gregg",
  "a": "http://xmlns.com/foaf/0.1/Person",
  "name": "Gregg Kellogg"

}

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

In the example above, the blogPost term has been marked as a data annotation container . The en , de , and ja keys will effectively Since keywords cannot be ignored semantically, but preserved syntactically, by the JSON-LD Processor as annotations . The interpretation of the data above is expressed in the table below. Note how the annotations do redefined, they can also not appear in the Linked Data below, but would continue to exist if the document were compacted or expanded using a JSON-LD processor: Subject Property Object Datatype http://example.com/ http://www.w3.org/1999/02/22-rdf-syntax-ns#type http://schema.org/Blog http://example.com/ http://schema.org/name World Financial News http://example.com/ http://schema.org/blogPost http://example.com/posts/1/en http://example.com/ http://schema.org/blogPost http://example.com/posts/1/de http://example.com/posts/1/en http://schema.org/articleBody World commodities were up today with heavy trading of crude oil... http://example.com/posts/1/en http://schema.org/wordCount 1539 http://www.w3.org/2001/XMLSchema#integer http://example.com/posts/1/en http://example.com/schema/commentCount 64 http://www.w3.org/2001/XMLSchema#integer http://example.com/posts/1/de http://schema.org/articleBody Welt Rohstoffe waren bis heute mit schweren Handel mit Rohöl... http://example.com/posts/1/de http://schema.org/wordCount 1204 http://www.w3.org/2001/XMLSchema#integer http://example.com/posts/1/de http://example.com/schema/commentCount 23 http://www.w3.org/2001/XMLSchema#integer 6.15 Explicitly Ignoring Data At times, it becomes necessary be aliased to explicitly ignore data expressed other keywords. Every statement in JSON documents because it has no semantic meaning. For example, when the @vocab keyword is used, every key in context having a JSON-LD object is appended to the vocabulary IRI . The author may not want that behavior to apply to every key, and it may be easier to specify just the keys that they want the JSON-LD processor to ignore. For this purpose, an author may associate the null keyword with a term in the JSON-LD Context. { "@context": { "@vocab": "http://schema.org/", }, "name": "Manu Sporny", "description": "That guy", "gender": "Male", } In the example above, the author has used @vocab as the base IRI for all terms key (as in the document, but has expressed that the databaseId { "@type": ... } value should not ) will be processed by the JSON-LD processor by associating it with the null keyword in the JSON-LD Context. ignored when being processed.

6.16 6.14 Expanded Document Form

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

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

{
   "@context":

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

      "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/"

   "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:

[
  {
    "http://xmlns.com/foaf/0.1/name": [
      { "@value": "Manu Sporny" }

    "http://xmlns.com/foaf/0.1/name": [
      { "@value": "Manu Sporny" }

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

    "http://xmlns.com/foaf/0.1/homepage": [
      { "@id": "http://manu.sporny.org/" }

    ]
  }
]

Expanded document form is useful when an application has to process input data in a deterministic form. It has been optimized to ensure that the code that developers have to write is minimized compared to the code that would have to be written to operate on 6.17 6.15 Compact Document Form .

6.17 6.15 Compact Document Form

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

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

[
  {
    "http://xmlns.com/foaf/0.1/name": [ "Manu Sporny" ],
    "http://xmlns.com/foaf/0.1/homepage": [

    "http://xmlns.com/foaf/0.1/name": [ "Manu Sporny" ],
    "http://xmlns.com/foaf/0.1/homepage": [

      {
       "@id": "http://manu.sporny.org/"

       "@id": "http://manu.sporny.org/"

      }
    ]
  }
]

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

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

    }
  }
}

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

{
  "@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/"

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

}

The compaction algorithm enables a developer to map any document into an application-specific compacted form by first form. The process consists of expanding the document (see 6.16 6.14 Expanded Document Form . ) and then using a developer-supplied context to compact the expanded document. While the context provided above mapped http://xmlns.com/foaf/0.1/name to name , it could have also mapped it to any arbitrary string term provided by the developer. This powerful mechanism allows the developer to re-shape the incoming JSON data into a format that is optimized for their application.

6.16 Data Indexing

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. Often this data does not have any 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 simpley 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:

{
  "@context":
  {
     "schema": "http://schema.org/",
     "name": "schema:name",
     "body": "schema:articleBody",
     "words": "schema:wordCount",
     "post": {
       "@id": "schema:blogPost",
       "@container": "@index"
     }
  },
  "@id": "http://example.com/",
  "@type": "schema:Blog",
  "name": "World Financial News",
  "post": {
     "en": {
       "@id": "http://example.com/posts/1/en",
       "body": "World commodities were up today with heavy trading of crude oil...",
       "words": 1539
     },
     "de": {
       "@id": "http://example.com/posts/1/de",
       "body": "Die Werte an Warenbörsen stiegen im Sog eines starken Handels von Rohöl...",
       "words": 1204
     }
  }
}

In the example above, the blogPost term has been marked as an index map . The en , de , and ja keys will be ignored semantically, but preserved syntactically, by the JSON-LD Processor. This allows a developer to access the German version of the blogPost using the following code snippet: obj.blogPost.de .

The interpretation of the data above is expressed in the table below. Note how the index keys do not appear in the Linked Data below, but would continue to exist if the document were compacted or expanded (see 6.15 Compact Document Form and 6.14 Expanded Document Form ) using a JSON-LD processor: