Get or construct RDF Triples

An raptor_statement can be made either by receiving them from a raptor_parser via parsing or can be constructed by hand.

When constructing by hand, the raptor_statement structure should be allocated by the application and the fields filled in. Each triple has three parts. The subject can be a URI or blank node, the predicate can only be a URI and the object can be a URI, blank node or RDF literal. RDF literals can have either just a Unicode string, a Unicode string and a language or a Unicode string and a datatype URI.

The triple part types are set as fields named like subject_type for describing field subject. So to initialise the subject of the triple, set the field statement.subject to point to a previously allocated raptor_uri* object (for URI) or char* (for blank node) and set statement.subject_type to RAPTOR_IDENTIFIER_TYPE_RESOURCE or RAPTOR_IDENTIFIER_TYPE_ANONYMOUS respectively. Triple predicates are always of type RAPTOR_IDENTIFIER_TYPE_RESOURCE. Triple objects are all all types given above and also RAPTOR_IDENTIFIER_TYPE_LITERAL which takes an unsigned char* pointer plus an optional language char* pointer in the object_literal_language field OR a a raptor_uri* literal datatype pointer in the object_literal_datatype field. The triple part types are described under raptor_identifier_type.

Example 3. rdfserialize.c: Serialize 1 triple to RDF/XML (Abbreviated)

#include <stdio.h>
#include <raptor.h>
#include <stdlib.h>

/* rdfserialize.c: serialize 1 triple to RDF/XML-Abbrev */

int
main(int argc, char *argv[])
{
  raptor_serializer* rdf_serializer=NULL;
  unsigned char *uri_string;
  raptor_uri *base_uri;
  raptor_statement* triple;

  raptor_init();
  
  uri_string=raptor_uri_filename_to_uri_string(argv[1]);
  base_uri=raptor_new_uri(uri_string);

  rdf_serializer=raptor_new_serializer("rdfxml-abbrev");
  raptor_serialize_start_to_file_handle(rdf_serializer, base_uri, stdout);
  
  /* Make a triple with URI subject, URI predicate, literal object */
  triple=(raptor_statement*)calloc(1, sizeof(raptor_statement));
  triple->subject=(void*)raptor_new_uri((const unsigned char*)"http://example.org/subject");
  triple->subject_type=RAPTOR_IDENTIFIER_TYPE_RESOURCE;
  triple->predicate=(void*)raptor_new_uri((const unsigned char*)"http://example.org/predicate");
  triple->predicate_type=RAPTOR_IDENTIFIER_TYPE_RESOURCE;
  triple->object="An example literal";
  triple->object_type=RAPTOR_IDENTIFIER_TYPE_LITERAL;
  triple->object_literal_language=(const unsigned char*)"en";

  /* Write the triple */
  raptor_serialize_statement(rdf_serializer, triple);

  /* Delete the triple */
  raptor_free_uri((raptor_uri*)triple->subject);
  raptor_free_uri((raptor_uri*)triple->predicate);
  free(triple);

  raptor_serialize_end(rdf_serializer);
  raptor_free_serializer(rdf_serializer);
  
  raptor_free_uri(base_uri);
  raptor_free_memory(uri_string);

  raptor_finish();
  return 0;
}

Compile it like this:

$ gcc -o rdfserialize rdfserialize.c `raptor-config --cflags` `raptor-config --libs`

and run it with an optional base URI argument

$ ./rdfserialize
<?xml version="1.0" encoding="utf-8"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Description rdf:about="http://example.org/subject">
    <ns0:predicate xmlns:ns0="http://example.org/" xml:lang="en">An example</ns0:predicate>
  </rdf:Description>
</rdf:RDF>