Notes on the rdf/json format
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README.md

README.md

This is a specification for a resource-centric serialisation of RDF in JSON. It aims to serialise RDF in a structure that is easy for developers to work with. More background can be found in the RDF/JSON wiki.

Syntax Specification

RDF/JSON represents a set of RDF triples as a series of nested data structures. Each unique subject in the set of triples is represented as a key in JSON object (also known as associative array, dictionary or hash table). The value of each key is a object whose keys are the URIs of the properties associated with each subject. The value of each property key is an array of objects representing the value of each property.

Blank node subjects are named using a string conforming to the nodeID production in Turtle. For example: _:A1

In general, a triple (subject S, predicate P, object O) is encoded in the following structure:

{ "S" : { "P" : [ O ] } }

The object of the triple O is represented as a further JSON object with the following keys:

  • type - one of 'uri', 'literal' or 'bnode' (required and must be lowercase)
  • value - the lexical value of the object (required, full URIs should be used, not qnames)
  • lang - the language of a literal value (optional but if supplied it must not be empty) as defined by RFC3066
  • datatype -the datatype URI of the literal value (optional) as defined by RFC3986

The 'lang' and 'datatype' keys should only be used if the value of the 'type' key is "literal".

For example, the following triple:

<http://example.org/about> <http://purl.org/dc/elements/1.1/title> "Anna's Homepage" .

can be encoded in RDF/JSON as:

    {
      "http://example.org/about" : 
        {
           "http://purl.org/dc/elements/1.1/title": [ { "type" : "literal" , "value" : "Anna's Homepage" } ]
        }
    }

Here is an example of the RDF JSON specification in the format of a JSON Schema. The latest version can also be found in the schema section of the SOAPjr.org site.

    {
         "version":"0.3.0",
         "id":"RDF-JSON",
         "description":"RDF JSON definition",
         "type":"object",
         "properties":{
         },
         "additionalProperties":{
             "type":"object",
             "description":"subject (root object)",
             "optional":"true",
             "properties":{
             },
         "additionalProperties":{
             "type":"array",
             "description":"predicate (subject object)",
             "optional":"true",
             "items":{
                 "type":"object",
                 "description":"object (value array)",
                 "properties":{
                     "description":"content (value object)",
                     "type":{
                         "type":"string",
                         "enum":["uri","bnode","literal"]
                     },
                     "value":{
                         "type":"string"
                     },
                     "lang":{
                         "optional":true,
                         "description":"See ftp://ftp.isi.edu/in-notes/bcp/bcp47.txt",
                         "type":"string"
                     },
                     "datatype":{
                         "optional":true,
                         "format":"uri",
                         "type":"string"
                     }
                 }
             }
         }
       }
    }

Examples

The following RDF/XML:

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:foaf="http://xmlns.com/foaf/0.1/"
  xmlns:dc="http://purl.org/dc/elements/1.1/">
  <rdf:Description rdf:about="http://example.org/about">
    <dc:creator>Anna Wilder</dc:creator>
    <dc:title xml:lang="en">Anna's Homepage</dc:title>
    <foaf:maker rdf:nodeID="person" />
  </rdf:Description>
  <rdf:Description rdf:nodeID="person">
    <foaf:homepage rdf:resource="http://example.org/about" />
    <foaf:made rdf:resource="http://example.org/about" />
    <foaf:name>Anna Wilder</foaf:name>
    <foaf:firstName>Anna</foaf:firstName>
    <foaf:surname>Wilder</foaf:surname>
    <foaf:depiction rdf:resource="http://example.org/pic.jpg" />
    <foaf:nick>wildling</foaf:nick>
    <foaf:nick>wilda</foaf:nick>
    <foaf:mbox_sha1sum>69e31bbcf58d432950127593e292a55975bc66fd</foaf:mbox_sha1sum>
  </rdf:Description>
</rdf:RDF>

Can be represented as the following RDF/JSON structure:

    {
        "http://example.org/about" : {
            "http://purl.org/dc/elements/1.1/creator" : [ { "value" : "Anna Wilder", "type" : "literal" } ],
            "http://purl.org/dc/elements/1.1/title"   : [ { "value" : "Anna's Homepage", "type" :  "literal", "lang" : "en" } ] ,
            "http://xmlns.com/foaf/0.1/maker"         : [ { "value" : "_:person", "type" : "bnode" } ]
        } ,
 
        "_:person" : {
            "http://xmlns.com/foaf/0.1/homepage"      : [ { "value" : "http://example.org/about", "type" : "uri" } ] ,
            "http://xmlns.com/foaf/0.1/made"          : [ { "value" : "http://example.org/about", "type" : "uri" } ] ,
            "http://xmlns.com/foaf/0.1/name"          : [ { "value" : "Anna Wilder", "type" : "literal" } ] ,
            "http://xmlns.com/foaf/0.1/firstName"     : [ { "value" : "Anna", "type" : "literal" } ] ,
            "http://xmlns.com/foaf/0.1/surname"       : [ { "value" : "Wilder", "type" : "literal" } ] , 
            "http://xmlns.com/foaf/0.1/depiction"     : [ { "value" : "http://example.org/pic.jpg", "type" : "uri" } ] ,
            "http://xmlns.com/foaf/0.1/nick"          : [ 
                                                          { "type" : "literal", "value" : "wildling"} , 
                                                          { "type" : "literal", "value" : "wilda" } 
                                                    ] ,
            "http://xmlns.com/foaf/0.1/mbox_sha1sum"  : [ {  "value" : "69e31bbcf58d432950127593e292a55975bc66fd", "type" : "literal" } ] 
        }
    }

Serialisation Algorithm

Refer to http://json.org/ for definitions of terminology

1. Start a JSON object (called the root object)
2. Group all the triples by subject
3. For each subject:
   1. Create a JSON object for the subject (called the subject object)
   2. Group all triples having the current subject by predicate
   3. For each predicate:
        1. Create a JSON array (called the value array)
        2. Select all triples having the current subject and current predicate
        3. For each value:
            1. Create a JSON object (called the value object)
            2. Add a key/value pair to the value object with the key being the string
               "value" and the value being the lexical value of the triple value
            3. Add a key/value pair to the value object with the key being the string
               "type" and the value being one of "literal", "uri" or "bnode" depending
                on the type of the triple's value
            4. If the triple's value is a plain literal and has a language then add a 
               key/value pair to the value object with the key being the string "lang"
               and the value being the language token
            5. If the triple's value is a typed literal then add a key/value pair to 
               the value object with the key being the string "datatype" and value 
               being the URI of the datatype
            6. Push the value object onto the end of the value array
        4. Add a key/value pair to the subject object with the key being the predicate
           URI and the value being the value array
    4. Add a key/value pair to the root object with the key being the URI or blank node
       identifier of the subject and the value being the subject object created in the
       previous step

Publishing RDF/JSON on the web

If doing content-negotiation, respond to, and send the content-type as application/json. An empty graph (ie: no triples) should be served as an empty object: {}.

Historical Note

The research behind this specification is available as RDF JSON Brainstorming