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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="tutorial-serializer-get-triples"></a>Get or construct RDF Triples</h2></div></div></div>
<p>
An <a class="link" href="raptor-section-triples.html#raptor-statement" title="raptor_statement"><span class="type">raptor_statement</span></a>
can be made either by receiving them from a
<a class="link" href="raptor-section-parser.html#raptor-parser" title="raptor_parser"><span class="type">raptor_parser</span></a>
via parsing or can be constructed by hand.</p>
<p>When constructing by hand,
the <a class="link" href="raptor-section-triples.html#raptor-statement" title="raptor_statement"><span class="type">raptor_statement</span></a>
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.</p>
<p>The triple part types are set as fields named
like <code class="literal">subject_type</code> for describing
field <code class="literal">subject</code>.
So to initialise the subject of the triple,
set the field <code class="literal">statement.subject</code> to point to a
previously allocated
<a class="link" href="raptor-section-uri.html#raptor-uri" title="raptor_uri"><span class="type">raptor_uri*</span></a> object (for URI)
or <code class="literal">char*</code> (for blank node) and
set <code class="literal">statement.subject_type</code>
to <code class="literal">RAPTOR_IDENTIFIER_TYPE_RESOURCE</code> or
<code class="literal">RAPTOR_IDENTIFIER_TYPE_ANONYMOUS</code> respectively.
Triple predicates are always of type
<code class="literal">RAPTOR_IDENTIFIER_TYPE_RESOURCE</code>.
Triple objects are all all types given above and also
<code class="literal">RAPTOR_IDENTIFIER_TYPE_LITERAL</code> which takes
an <code class="literal">unsigned char*</code> pointer plus an optional
language <code class="literal">char*</code> pointer
in the <code class="literal">object_literal_language</code> field OR a
a <code class="literal">raptor_uri*</code> literal datatype pointer
in the <code class="literal">object_literal_datatype</code> field.
The triple part types are described under
<a class="link" href="raptor-section-triples.html#raptor-identifier-type" title="enum raptor_identifier_type"><span class="type">raptor_identifier_type</span>.</a>
</p>
<div class="example">
<a name="raptor-example-rdfserialize"></a><p class="title"><b>Example 3. <code class="filename">rdfserialize.c</code>: Serialize 1 triple to RDF/XML (Abbreviated)</b></p>
<div class="example-contents">
<pre class="programlisting">
#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*)malloc(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;
}
</pre>
<p>Compile it like this:
</p>
<pre class="screen">
$ gcc -o rdfserialize rdfserialize.c `raptor-config --cflags` `raptor-config --libs`
</pre>
<p>
and run it with an optional base URI argument
</p>
<pre class="screen">
$ ./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>
</pre>
<p>
</p>
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