RDF/PHP Specification

This is a specification for a resource-centric serialisation of RDF in PHP that is compatible with the internal data structure used by ARC and is similar in style to the RDF/JSON Specification.

Syntax Specification

RDF/PHP 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 a PHP 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 blank nodes 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 a further 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)
  • datatype the datatype URI of the literal value (optional)

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/PHP as:

array(
  "http://example.org/about" =>
    array(
       "http://purl.org/dc/elements/1.1/title" =>  array( array( "type" => "literal" , "value" => "Anna's Homepage." ), ),
    )
);

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/PHP structure:

array(
      "http://example.org/about" => array(
        "http://purl.org/dc/elements/1.1/creator" => array(
            array( "value" => "Anna Wilder", "type" => "literal" ) ) ,
                    "dc:title" => array(
            array( "value" => "Anna's Homepage", "type" => "literal", "lang" => "en" ) ) ,
                    "http://xmlns.com/foaf/0.1/maker" => array(
            array( "value" => "_:person", "type" => "bnode" ) )
      ) ,

      "_:person" => array(
        "http://xmlns.com/foaf/0.1/homepage" => array(
            array( "value" => "http://example.org/about", "type" => "uri" ) ) ,
                    "http://xmlns.com/foaf/0.1/made" => array(
            array( "value" => "http://example.org/about", "type" => "uri" ) ) ,
                    "http://xmlns.com/foaf/0.1/name" => array(
            array( "value" => "Anna Wilder", "type" => "literal" ) ) ,
                    "http://xmlns.com/foaf/0.1/firstName" => array(
            array( "value" => "Anna", "type" => "literal" ) ) ,
                    "http://xmlns.com/foaf/0.1/surname" => array(
            array( "value" => "Wilder", "type" => "literal" ) ) ,
                    "http://xmlns.com/foaf/0.1/depiction" => array(
            array( "value" => "http://example.org/pic.jpg", "type" => "uri" ) ) ,
                    "http://xmlns.com/foaf/0.1/nick" => array(
                    array( "type" => "literal", "value" => "wildling") ,
                     array( "type" => "literal", "value" => "wilda" ) ) ,
                    "http://xmlns.com/foaf/0.1/mbox_sha1sum" => array(
                        array(
                        "value" => "69e31bbcf58d432950127593e292a55975bc66fd",
                        "type" => "literal"
                        )
                    )
      )
);

History

The RDF/PHP Specification was written/edited 2008 by Ian Davis and Keith Alexander; originally published under http://n2.talis.com/wiki/RDF_PHP_Specification, which is no-longer available.

The content of this specification has been taken from the following locations:

This specification is a work of its own right and is licensed under Creative Commons Attribution-ShareAlike 3.0 Unported (CC-BY-SA-3.0).