JSON-LD 1.1

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 a compact IRI nor an absolute IRI (i.e., they do not contain a colon).

If @vocab is used but certain keys in an dictionary 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 member would not expand to an IRI causing the property to be dropped when expanding.

{
  "@context": {
    "@version": 1.1,
    "@base": "http://example/document",
    "@vocab": ""
  },
  "@id": "http://example.org/places#BrewEats",
  "@type": "#Restaurant",
  "#name": "Brew Eats"
  ...
}

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 according section 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 IRIs would resolve against that IRI:

{
  "@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 absolute IRI, a context may define an @base mapping, to overwrite the base IRI for the document.

Setting @base to null will prevent relative IRIs from being expanded to absolute IRIs.

Please note that the @base will be ignored if used in external contexts.

4.1.4 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 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 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 the active 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 absolute 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:

In JSON-LD 1.0, 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]). The previous specification allows any term to be chosen as a compact IRI prefix, which led to a poor experience.

In JSON-LD 1.1, 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, or if their expanded term definition contains a @prefix member with the value true.

When processing mode is set to json-ld-1.1, terms will be used as compact IRI prefixes when compacting only if their expanded term definition contains a @prefix member with the value true, or if it has a a simple term definition where the value ends with a URI gen-delim character (e.g, /, # and others, see [RFC3986]).

In this case, the compact-iris term would not normally be usable as a prefix, both because it is defined with an expanded term definition, and because it's @id does not end in a gen-delim character. Adding "@prefix": true allows it to be used as the prefix portion of the compact IRI compact-iris:are-considered.

4.1.5 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 aliases url and a, respectively.

Other than for @type, properties of expanded term definitions where the term is a keyword are be ignored.

When processing mode is set to json-ld-1.1, @type may be used with an expanded term definition with @container set to @set; no other members 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.

{
  "@context": {
    "@version": 1.1,
    "@type": {"@container": "@set"}
  },
  "@type": ["http:/example.org/type"]
}

Since keywords cannot be redefined, they can also not be aliased to other keywords.

4.1.6 IRI Expansion within a Context

This section is non-normative.

In general, normal IRI expansion rules apply anywhere an IRI is expected (see section 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:

{
  "@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 another term:

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

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

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

In this example, the compact IRI form is used in two different ways. In the first approach, foaf:age declares both the IRI for the term (using short-form) as well as the @type associated with the term. In the second approach, only the @type associated with the term is specified. The 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": {
      "@id": "foaf:age",
      "@type": "xsd:integer"
    },
    "http://xmlns.com/foaf/0.1/homepage": {
      "@type": "@id"
    }
  },
  ...
}

In order for the absolute IRI to match above, the absolute IRI needs to be used in the JSON-LD document. Also note that foaf:homepage will not use the { "@type": "@id" } declaration because foaf:homepage is not the same as http://xmlns.com/foaf/0.1/homepage. That is, 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 term1 cannot depend on the definition of term2 if term2 also depends on term1. For example, the following context definition is illegal:

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

4.2.1 Typed Values

This section is non-normative.

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 an @context section.
2. By utilizing a value object.
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:

The modified key's value above is automatically type coerced to 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 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.

A node type specifies the type of thing that is being described, like a person, place, event, or web page. A value type specifies the data type of a particular value, such as an integer, a floating point number, or a date.

{
  ...
  "@id": "http://example.org/posts#TripToWestVirginia",
  "@type": "http://schema.org/BlogPosting",  ← This is a node type
  "http://purl.org/dc/terms/modified": {
    "@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 dictionary, the @type keyword is expressing a value type. Otherwise, the @type keyword is expressing a node type. The example above expresses the following data:

4.2.2 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 values by 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 a term coerced to @id or @vocab is to be interpreted as an IRI. The difference between @id and @vocab is how values are expanded to absolute IRIs. @vocab first tries to expand the value by interpreting it as term. If no matching term is found in the active context, it tries to expand it as compact IRI or absolute IRI if there's a colon in the value; otherwise, it will expand the value using the active context's vocabulary mapping, if present. Values coerced to @id in contrast are expanded as compact IRI or absolute IRI if a colon is present; otherwise, they are interpreted as relative IRI.

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

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

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

In this case the @id definition in the term definition is optional. If it does exist, the compact IRI or 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, expanded IRI http://xmlns.com/foaf/0.1/age.

4.2.3 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 code with the two strings 花澄 and 科学者. Languages codes are defined in [BCP47]. The default language applies to all string values that are not type coerced.

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

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

Second, it is possible to associate a language with a specific term using an expanded term definition:

{
  "@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 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 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.

{
  "@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 the property.language pattern. 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 a value object:

{
  "@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:

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

See section 9.6 Language Maps for a description of using language maps to set the language of mapped values.

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 and rdf:rest, with the end of the list defined as the resource rdf:nil. This can be represented as statments, as the "statements" tab illustrates.

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. For example, in GeoJSON (see [RFC7946]), coordinates are an ordered list of positions, which are represented as an array of two or more numbers:

{
  "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 definion:

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 section 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 is maintained 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 section 4.6 Indexed Values for a further discussion.

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. The blank 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.

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

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 section 5.2 Compacted Document Form and section 5.1 Expanded Document Form) using a JSON-LD processor.

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.

If the processing mode is set to json-ld-1.1, the special index @none is used for indexing data which does not have an associated index, which is useful to maintain a normalized representation.

4.6.2 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 an language map. The en and de 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.

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.

If the processing mode is set to json-ld-1.1, the special index @none is used for indexing data which does not have a language, which is useful to maintain a normalized representation.