path: root/src/raptor_serialize_rdfxml.c

/* -*- Mode: c; c-basic-offset: 2 -*-
 *
 * raptor_serialize_rdfxml.c - RDF/XML serializer
 *
 * Copyright (C) 2004-2008, David Beckett http://www.dajobe.org/
 * Copyright (C) 2004-2005, University of Bristol, UK http://www.bristol.ac.uk/
 *
 * This package is Free Software and part of Redland http://librdf.org/
 *
 * It is licensed under the following three licenses as alternatives:
 *   1. GNU Lesser General Public License (LGPL) V2.1 or any newer version
 *   2. GNU General Public License (GPL) V2 or any newer version
 *   3. Apache License, V2.0 or any newer version
 *
 * You may not use this file except in compliance with at least one of
 * the above three licenses.
 *
 * See LICENSE.html or LICENSE.txt at the top of this package for the
 * complete terms and further detail along with the license texts for
 * the licenses in COPYING.LIB, COPYING and LICENSE-2.0.txt respectively.
 *
 */

#ifdef HAVE_CONFIG_H
#include <raptor_config.h>
#endif

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdarg.h>
#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif

/* Raptor includes */
#include "raptor2.h"
#include "raptor_internal.h"


/*
 * Raptor RDF/XML serializer object
 */
typedef struct {
  /* Namespace stack */
  raptor_namespace_stack *nstack;

  /* the xml: namespace - this is destroyed when nstack above is deleted */
  raptor_namespace *xml_nspace;

  /* the rdf: namespace - this is destroyed when nstack above is deleted */
  raptor_namespace *rdf_nspace;

  /* the rdf:RDF element */
  raptor_xml_element* rdf_RDF_element;

  /* where the xml is being written */
  raptor_xml_writer *xml_writer;

  /* User declared namespaces */
  raptor_sequence *namespaces;

  /* non zero if rdf:RDF has been written (and thus no new namespaces
   * can be declared).
   */
  int written_header;
} raptor_rdfxml_serializer_context;


/* local prototypes */

static void
raptor_rdfxml_serialize_terminate(raptor_serializer* serializer);

/* create a new serializer */
static int
raptor_rdfxml_serialize_init(raptor_serializer* serializer, const char *name)
{
  raptor_rdfxml_serializer_context* context = (raptor_rdfxml_serializer_context*)serializer->context;

  context->nstack = raptor_new_namespaces(serializer->world, 1);
  if(!context->nstack)
    return 1;
  context->xml_nspace = raptor_new_namespace(context->nstack,
                                             (const unsigned char*)"xml",
                                             (const unsigned char*)raptor_xml_namespace_uri,
                                             0);

  context->rdf_nspace = raptor_new_namespace(context->nstack,
                                             (const unsigned char*)"rdf",
                                             (const unsigned char*)raptor_rdf_namespace_uri,
                                             0);

  context->namespaces = raptor_new_sequence(NULL, NULL);

  if(!context->xml_nspace || !context->rdf_nspace || !context->namespaces) {
    raptor_rdfxml_serialize_terminate(serializer);
    return 1;
  }

  /* Note: item 0 in the list is rdf:RDF's namespace */
  if(raptor_sequence_push(context->namespaces, context->rdf_nspace)) {
    raptor_rdfxml_serialize_terminate(serializer);
    return 1;
  }

  return 0;
}


/* destroy a serializer */
static void
raptor_rdfxml_serialize_terminate(raptor_serializer* serializer)
{
  raptor_rdfxml_serializer_context* context = (raptor_rdfxml_serializer_context*)serializer->context;

  if(context->xml_writer) {
    raptor_free_xml_writer(context->xml_writer);
    context->xml_writer = NULL;
  }

  if(context->rdf_RDF_element) {
    raptor_free_xml_element(context->rdf_RDF_element);
    context->rdf_RDF_element = NULL;
  }

  if(context->rdf_nspace) {
    raptor_free_namespace(context->rdf_nspace);
    context->rdf_nspace = NULL;
  }

  if(context->xml_nspace) {
    raptor_free_namespace(context->xml_nspace);
    context->xml_nspace = NULL;
  }

  if(context->namespaces) {
    int i;

    /* Note: item 0 in the list is rdf:RDF's namespace and freed above */
    for(i = 1; i< raptor_sequence_size(context->namespaces); i++) {
      raptor_namespace* ns = (raptor_namespace*)raptor_sequence_get_at(context->namespaces, i);
      if(ns)
        raptor_free_namespace(ns);
    }
    raptor_free_sequence(context->namespaces);
    context->namespaces = NULL;
  }

  if(context->nstack) {
    raptor_free_namespaces(context->nstack);
    context->nstack = NULL;
  }
}


#define RDFXML_NAMESPACE_DEPTH 0

/* add a namespace */
static int
raptor_rdfxml_serialize_declare_namespace_from_namespace(raptor_serializer* serializer,
                                                         raptor_namespace *nspace)
{
  raptor_rdfxml_serializer_context* context = (raptor_rdfxml_serializer_context*)serializer->context;
  int i;

  if(context->written_header)
    return 1;

  for(i = 0; i< raptor_sequence_size(context->namespaces); i++) {
    raptor_namespace* ns;
    ns = (raptor_namespace*)raptor_sequence_get_at(context->namespaces, i);

    /* If prefix is already declared, ignore it */
    if(!ns->prefix && !nspace->prefix)
      return 1;

    if(ns->prefix && nspace->prefix &&
       !strcmp((const char*)ns->prefix, (const char*)nspace->prefix))
      return 1;

    if(ns->uri && nspace->uri &&
       raptor_uri_equals(ns->uri, nspace->uri))
      return 1;
  }

  nspace = raptor_new_namespace_from_uri(context->nstack,
                                         nspace->prefix, nspace->uri,
                                         RDFXML_NAMESPACE_DEPTH);
  if(!nspace)
    return 1;

  raptor_sequence_push(context->namespaces, nspace);
  return 0;
}


/* add a namespace */
static int
raptor_rdfxml_serialize_declare_namespace(raptor_serializer* serializer,
                                          raptor_uri *uri,
                                          const unsigned char *prefix)
{
  raptor_rdfxml_serializer_context* context = (raptor_rdfxml_serializer_context*)serializer->context;
  raptor_namespace *ns;
  int rc;

  ns = raptor_new_namespace_from_uri(context->nstack, prefix, uri,
                                     RDFXML_NAMESPACE_DEPTH);

  rc = raptor_rdfxml_serialize_declare_namespace_from_namespace(serializer,
                                                                 ns);
  raptor_free_namespace(ns);

  return rc;
}


/* start a serialize */
static int
raptor_rdfxml_serialize_start(raptor_serializer* serializer)
{
  raptor_rdfxml_serializer_context* context = (raptor_rdfxml_serializer_context*)serializer->context;
  raptor_xml_writer* xml_writer;
  raptor_option option;
  
  if(context->xml_writer) {
    raptor_free_xml_writer(context->xml_writer);
    context->xml_writer = NULL;
  }

  xml_writer = raptor_new_xml_writer(serializer->world, context->nstack,
                                     serializer->iostream);
  if(!xml_writer)
    return 1;

  option = RAPTOR_OPTION_WRITER_XML_VERSION;
  raptor_xml_writer_set_option(xml_writer, option, NULL,
                               RAPTOR_OPTIONS_GET_NUMERIC(serializer, option));
  option = RAPTOR_OPTION_WRITER_XML_DECLARATION;
  raptor_xml_writer_set_option(xml_writer, option, NULL,
                               RAPTOR_OPTIONS_GET_NUMERIC(serializer, option));

  context->xml_writer = xml_writer;
  context->written_header = 0;

  return 0;
}


static int
raptor_rdfxml_ensure_writen_header(raptor_serializer* serializer,
                                   raptor_rdfxml_serializer_context* context)
{
  raptor_xml_writer* xml_writer;
  raptor_uri *base_uri;
  int i;
  raptor_qname **attrs = NULL;
  int attrs_count = 0;
  int rc = 1;

  if(context->written_header)
    return 0;

  context->written_header = 1;

  xml_writer = context->xml_writer;

  base_uri = serializer->base_uri;
  if(base_uri)
    base_uri = raptor_uri_copy(base_uri);

  context->rdf_RDF_element = raptor_new_xml_element_from_namespace_local_name(context->rdf_nspace, (const unsigned char*)"RDF", NULL, base_uri);
  if(!context->rdf_RDF_element)
    goto tidy;

  /* NOTE: Starts it item 1 as item 0 is the element's namespace (rdf)
   * and does not need to be declared
   */
  for(i = 1; i< raptor_sequence_size(context->namespaces); i++) {
    raptor_namespace* ns = (raptor_namespace*)raptor_sequence_get_at(context->namespaces, i);
    if(raptor_xml_element_declare_namespace(context->rdf_RDF_element, ns))
      goto tidy;
  }

  if(base_uri &&
     RAPTOR_OPTIONS_GET_NUMERIC(serializer, RAPTOR_OPTION_WRITE_BASE_URI)) {
    const unsigned char* base_uri_string;

    attrs = RAPTOR_CALLOC(raptor_qname **, 1, sizeof(raptor_qname*));
    if(!attrs)
      goto tidy;

    base_uri_string = raptor_uri_as_string(base_uri);
    attrs[attrs_count] = raptor_new_qname_from_namespace_local_name(serializer->world, context->xml_nspace, (const unsigned char*)"base",  base_uri_string);
    if(!attrs[attrs_count]) {
      RAPTOR_FREE(qnamearray, attrs);
      goto tidy;
    }
    attrs_count++;
  }

  if(attrs_count)
    raptor_xml_element_set_attributes(context->rdf_RDF_element, attrs,
                                      attrs_count);
  else
    raptor_xml_element_set_attributes(context->rdf_RDF_element, NULL, 0);


  raptor_xml_writer_start_element(xml_writer, context->rdf_RDF_element);
  raptor_xml_writer_raw_counted(xml_writer, (const unsigned char*)"\n", 1);

  rc = 0;

  tidy:
  if(base_uri)
    raptor_free_uri(base_uri);

  return rc;
}


/* serialize a statement */
static int
raptor_rdfxml_serialize_statement(raptor_serializer* serializer,
                                  raptor_statement *statement)
{
  raptor_rdfxml_serializer_context* context = (raptor_rdfxml_serializer_context*)serializer->context;
  raptor_xml_writer* xml_writer = context->xml_writer;
  unsigned char* uri_string = NULL; /* predicate URI */
  unsigned char* name = NULL;  /* where to split predicate name */
  unsigned char* subject_uri_string = NULL;
  unsigned char* object_uri_string = NULL;
  const unsigned char* nsprefix = (const unsigned char*)"ns0";
  int rc = 1;
  size_t len;
  raptor_xml_element* rdf_Description_element = NULL;
  raptor_uri* predicate_ns_uri = NULL;
  raptor_namespace* predicate_ns = NULL;
  int free_predicate_ns = 0;
  raptor_xml_element* predicate_element = NULL;
  raptor_qname **attrs = NULL;
  int attrs_count = 0;
  raptor_uri* base_uri = NULL;
  raptor_term_type object_type;
  int allocated = 1;
  int object_is_parseTypeLiteral = 0;
  
  if(raptor_rdfxml_ensure_writen_header(serializer, context))
    return 1;

  if(statement->predicate->type == RAPTOR_TERM_TYPE_URI) {
    unsigned char *p;
    size_t uri_len;
    size_t name_len = 1;
    unsigned char c;

    /* Do not use raptor_uri_as_counted_string() - we want a modifiable copy */
    uri_string = raptor_uri_to_counted_string(statement->predicate->value.uri,
                                              &uri_len);
    if(!uri_string)
      goto oom;

    p= uri_string;
    name_len = uri_len;
    /* FIXME: this loop could be made smarter */
    while(name_len >0) {
      if(raptor_xml_name_check(p, name_len, 10)) {
        name = p;
        break;
      }
      p++; name_len--;
    }

    if(!name || (name == uri_string)) {
      raptor_log_error_formatted(serializer->world, RAPTOR_LOG_LEVEL_ERROR, NULL,
                                 "Cannot split predicate URI %s into an XML qname - skipping statement", uri_string);
      rc = 0; /* skip but do not return an error */
      goto tidy;
    }

    c = *name; *name = '\0';
    predicate_ns_uri = raptor_new_uri(serializer->world, uri_string);
    *name = c;
    if(!predicate_ns_uri)
      goto oom;

    predicate_ns = raptor_namespaces_find_namespace_by_uri(context->nstack,
                                                           predicate_ns_uri);
    if(!predicate_ns) {
      predicate_ns = raptor_new_namespace_from_uri(context->nstack,
                                                   nsprefix,
                                                   predicate_ns_uri, 0);
      if(!predicate_ns) {
        raptor_free_uri(predicate_ns_uri);
        goto oom;
      }
      free_predicate_ns = 1;
    }
    raptor_free_uri(predicate_ns_uri);
  } else {
    raptor_log_error_formatted(serializer->world, RAPTOR_LOG_LEVEL_ERROR, NULL,
                               "Cannot serialize a triple with subject node type %u\n",
                               statement->predicate->type);
    goto tidy;
  }

  /* base uri */
  if(serializer->base_uri)
    base_uri = raptor_uri_copy(serializer->base_uri);


  rdf_Description_element = raptor_new_xml_element_from_namespace_local_name(context->rdf_nspace,
                                                                             (unsigned const char*)"Description",
                                                                             NULL, base_uri);
  if(!rdf_Description_element)
    goto oom;

  attrs = RAPTOR_CALLOC(raptor_qname**, 3, sizeof(raptor_qname*));
  if(!attrs)
    goto oom;
  attrs_count = 0;

  /* subject */
  switch(statement->subject->type) {
    case RAPTOR_TERM_TYPE_BLANK:
      attrs[attrs_count] = raptor_new_qname_from_namespace_local_name(serializer->world, context->rdf_nspace, (const unsigned char*)"nodeID",
                                                                      statement->subject->value.blank.string);
      if(!attrs[attrs_count])
        goto oom;
      attrs_count++;
      break;

    case RAPTOR_TERM_TYPE_URI:
      allocated = 1;
      if(RAPTOR_OPTIONS_GET_NUMERIC(serializer, RAPTOR_OPTION_RELATIVE_URIS)) {
        subject_uri_string = raptor_uri_to_relative_uri_string(serializer->base_uri,
                                                               statement->subject->value.uri);
        if(!subject_uri_string)
          goto oom;
      } else {
        subject_uri_string = raptor_uri_as_string(statement->subject->value.uri);
        allocated = 0;
      }

      attrs[attrs_count] = raptor_new_qname_from_namespace_local_name(serializer->world, context->rdf_nspace, (const unsigned char*)"about",  subject_uri_string);
      if(!attrs[attrs_count]) {
        if(allocated)
          RAPTOR_FREE(char*, subject_uri_string);
        goto oom;
      }
      attrs_count++;

      if(allocated)
        RAPTOR_FREE(char*, subject_uri_string);

      break;

    case RAPTOR_TERM_TYPE_LITERAL:
      raptor_log_error(serializer->world, RAPTOR_LOG_LEVEL_ERROR, NULL, "Cannot serialize a triple with a literal subject\n");
      break;

    case RAPTOR_TERM_TYPE_UNKNOWN:
    default:
      raptor_log_error_formatted(serializer->world, RAPTOR_LOG_LEVEL_ERROR, NULL,
                                 "Cannot serialize a triple with subject node type %u",
                                 statement->subject->type);
  }

  if(attrs_count) {
    raptor_xml_element_set_attributes(rdf_Description_element, attrs, attrs_count);
    attrs = NULL; /* attrs ownership transferred to element */
  }

  raptor_xml_writer_cdata_counted(xml_writer, (const unsigned char*)"  ", 2);
  raptor_xml_writer_start_element(xml_writer, rdf_Description_element);
  raptor_xml_writer_cdata_counted(xml_writer, (const unsigned char*)"\n", 1);


  /* predicate */
  predicate_element = raptor_new_xml_element_from_namespace_local_name(predicate_ns, name, NULL, base_uri);
  if(!predicate_element)
    goto oom;

  /* object */
  attrs = RAPTOR_CALLOC(raptor_qname**, 3, sizeof(raptor_qname*));
  if(!attrs)
    goto oom;
  attrs_count = 0;

  object_type = statement->object->type;
  switch(object_type) {
    case RAPTOR_TERM_TYPE_LITERAL:
      object_is_parseTypeLiteral = 0;
      if(statement->object->value.literal.datatype &&
         raptor_uri_equals(statement->object->value.literal.datatype,
                           RAPTOR_RDF_XMLLiteral_URI(serializer->world)))
        object_is_parseTypeLiteral = 1;

      if(statement->object->value.literal.language) {
        attrs[attrs_count] = raptor_new_qname(context->nstack,
                                              (unsigned char*)"xml:lang",
                                              statement->object->value.literal.language);
        if(!attrs[attrs_count])
          goto oom;
        attrs_count++;
      }
      len = statement->object->value.literal.string_len;

      if(object_is_parseTypeLiteral) {
        attrs[attrs_count] = raptor_new_qname_from_namespace_local_name(serializer->world, context->rdf_nspace, (const unsigned char*)"parseType", (const unsigned char*)"Literal");
        if(!attrs[attrs_count])
          goto oom;
        attrs_count++;

        raptor_xml_element_set_attributes(predicate_element, attrs, attrs_count);
        attrs = NULL; /* attrs ownership transferred to element */

        raptor_xml_writer_cdata_counted(xml_writer, (const unsigned char*)"    ", 4);
        raptor_xml_writer_start_element(xml_writer, predicate_element);

        /* Print without escaping XML */
        if(len)
          raptor_xml_writer_raw_counted(xml_writer,
                                        (const unsigned char*)statement->object->value.literal.string,
                                        RAPTOR_BAD_CAST(unsigned int, len));
      } else {
        if(statement->object->value.literal.datatype) {
          attrs[attrs_count] = raptor_new_qname_from_namespace_local_name(serializer->world, context->rdf_nspace, (const unsigned char*)"datatype", raptor_uri_as_string(statement->object->value.literal.datatype));
          if(!attrs[attrs_count])
            goto oom;
          attrs_count++;
        }
        raptor_xml_element_set_attributes(predicate_element, attrs, attrs_count);
        attrs = NULL; /* attrs ownership transferred to element */

        raptor_xml_writer_cdata_counted(xml_writer,
                                        (const unsigned char*)"    ", 4);
        raptor_xml_writer_start_element(xml_writer, predicate_element);

        if(len)
          raptor_xml_writer_cdata_counted(xml_writer,
                                          statement->object->value.literal.string,
                                          RAPTOR_BAD_CAST(unsigned int, len));
      }

      raptor_xml_writer_end_element(xml_writer, predicate_element);
      raptor_free_xml_element(predicate_element);
      predicate_element = NULL;
      raptor_xml_writer_cdata_counted(xml_writer, (const unsigned char*)"\n", 1);

      break;

    case RAPTOR_TERM_TYPE_BLANK:
      attrs[attrs_count] = raptor_new_qname_from_namespace_local_name(serializer->world, context->rdf_nspace, (const unsigned char*)"nodeID", statement->object->value.blank.string);
      if(!attrs[attrs_count])
        goto oom;
      attrs_count++;

      raptor_xml_element_set_attributes(predicate_element, attrs, attrs_count);
      attrs = NULL; /* attrs ownership transferred to element */

      raptor_xml_writer_cdata_counted(xml_writer,
                                      (const unsigned char*)"    ", 4);
      raptor_xml_writer_empty_element(xml_writer, predicate_element);
      raptor_xml_writer_cdata_counted(xml_writer, (const unsigned char*)"\n", 1);
      break;

    case RAPTOR_TERM_TYPE_URI:
      /* must be URI */
      if(RAPTOR_OPTIONS_GET_NUMERIC(serializer, RAPTOR_OPTION_RELATIVE_URIS)) {
        object_uri_string = raptor_uri_to_relative_uri_string(serializer->base_uri,
                                                              statement->object->value.uri);
      } else {
        object_uri_string = raptor_uri_to_string(statement->object->value.uri);
      }
      if(!object_uri_string)
        goto oom;

      attrs[attrs_count] = raptor_new_qname_from_namespace_local_name(serializer->world, context->rdf_nspace, (const unsigned char*)"resource", object_uri_string);
      RAPTOR_FREE(char*, object_uri_string);

      if(!attrs[attrs_count])
        goto oom;

      attrs_count++;
      raptor_xml_element_set_attributes(predicate_element, attrs, attrs_count);
      attrs = NULL; /* attrs ownership transferred to element */

      raptor_xml_writer_cdata_counted(xml_writer,
                                      (const unsigned char*)"    ", 4);
      raptor_xml_writer_empty_element(xml_writer, predicate_element);
      raptor_xml_writer_cdata_counted(xml_writer, (const unsigned char*)"\n", 1);
      break;

    case RAPTOR_TERM_TYPE_UNKNOWN:
    default:
      raptor_log_error_formatted(serializer->world, RAPTOR_LOG_LEVEL_ERROR, NULL,
                                 "Cannot serialize a triple with object node type %u",
                                 object_type);
  }

  raptor_xml_writer_cdata_counted(xml_writer,
                                  (const unsigned char*)"  ", 2);

  rc = 0; /* success */
  goto tidy;

  oom:
  raptor_log_error(serializer->world, RAPTOR_LOG_LEVEL_FATAL, NULL, 
                   "Out of memory");

  tidy:

  if(attrs)
    RAPTOR_FREE(qnamearray, attrs);

  if(predicate_element)
    raptor_free_xml_element(predicate_element);

  if(rdf_Description_element) {
    raptor_xml_writer_end_element(xml_writer, rdf_Description_element);
    raptor_xml_writer_cdata_counted(xml_writer, (const unsigned char*)"\n", 1);
    raptor_free_xml_element(rdf_Description_element);
  }

  if(base_uri)
    raptor_free_uri(base_uri);

  if(free_predicate_ns)
    raptor_free_namespace(predicate_ns);

  if(uri_string)
    RAPTOR_FREE(char*, uri_string);

  return rc;
}


/* end a serialize */
static int
raptor_rdfxml_serialize_end(raptor_serializer* serializer)
{
  raptor_rdfxml_serializer_context* context = (raptor_rdfxml_serializer_context*)serializer->context;
  raptor_xml_writer* xml_writer = context->xml_writer;

  if(xml_writer) {
    /* Make sure an empty RDF/XML document is written when 0 triples
     * were seen
     */

    /* ignore ret value */
    raptor_rdfxml_ensure_writen_header(serializer, context);

    if(context->rdf_RDF_element) {
      raptor_xml_writer_end_element(xml_writer, context->rdf_RDF_element);
      raptor_xml_writer_raw_counted(xml_writer, (const unsigned char*)"\n", 1);
    }

    raptor_xml_writer_flush(xml_writer);
  }

  if(context->rdf_RDF_element) {
    raptor_free_xml_element(context->rdf_RDF_element);
    context->rdf_RDF_element = NULL;
  }

  return 0;
}


/* finish the serializer factory */
static void
raptor_rdfxml_serialize_finish_factory(raptor_serializer_factory* factory)
{

}

static const char* const rdfxml_names[2] = { "rdfxml", NULL};

static const char* const rdfxml_uri_strings[3] = {
  "http://www.w3.org/ns/formats/RDF_XML",
  "http://www.w3.org/TR/rdf-syntax-grammar",
  NULL
};
  
#define RDFXML_TYPES_COUNT 2
static const raptor_type_q rdfxml_types[RDFXML_TYPES_COUNT + 1] = {
  { "application/rdf+xml", 19, 10},
  { "text/rdf", 8, 6},
  { NULL, 0, 0}
};

static int
raptor_rdfxml_serializer_register_factory(raptor_serializer_factory *factory)
{
  factory->desc.names = rdfxml_names;
  factory->desc.mime_types = rdfxml_types;

  factory->desc.label = "RDF/XML";
  factory->desc.uri_strings = rdfxml_uri_strings,

  factory->context_length     = sizeof(raptor_rdfxml_serializer_context);

  factory->init                = raptor_rdfxml_serialize_init;
  factory->terminate           = raptor_rdfxml_serialize_terminate;
  factory->declare_namespace   = raptor_rdfxml_serialize_declare_namespace;
  factory->declare_namespace_from_namespace   = raptor_rdfxml_serialize_declare_namespace_from_namespace;
  factory->serialize_start     = raptor_rdfxml_serialize_start;
  factory->serialize_statement = raptor_rdfxml_serialize_statement;
  factory->serialize_end       = raptor_rdfxml_serialize_end;
  factory->finish_factory      = raptor_rdfxml_serialize_finish_factory;

  return 0;
}



int
raptor_init_serializer_rdfxml(raptor_world* world)
{
  return !raptor_serializer_register_factory(world,
                                             &raptor_rdfxml_serializer_register_factory);
}