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<?php
/**
* EasyRdf
*
* LICENSE
*
* Copyright (c) 2009-2013 Nicholas J Humfrey. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* 3. The name of the author 'Nicholas J Humfrey" may be used to endorse or
* promote products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* @package EasyRdf
* @copyright Copyright (c) 2009-2013 Nicholas J Humfrey
* @license http://www.opensource.org/licenses/bsd-license.php
*/
/**
* Class to serialise an EasyRdf_Graph to Turtle
* with no external dependancies.
*
* http://www.w3.org/TR/turtle/
*
* @package EasyRdf
* @copyright Copyright (c) 2009-2013 Nicholas J Humfrey
* @license http://www.opensource.org/licenses/bsd-license.php
*/
class EasyRdf_Serialiser_Turtle extends EasyRdf_Serialiser
{
private $outputtedBnodes = array();
/**
* Given a IRI string, escape and enclose in angle brackets.
*
* @param string $resourceIri
* @return string
*/
public static function escapeIri($resourceIri)
{
$escapedIri = str_replace('>', '\\>', $resourceIri);
return "<$escapedIri>";
}
/**
* Given a string, enclose in quotes and escape any quotes in the string.
* Strings containing tabs, linefeeds or carriage returns will be
* enclosed in three double quotes (""").
*
* @param string $value
* @return string
*/
public static function quotedString($value)
{
if (preg_match('/[\t\n\r]/', $value)) {
$escaped = str_replace(array('\\', '"""'), array('\\\\', '\\"""'), $value);
return '"""'.$escaped.'"""';
} else {
$escaped = str_replace(array('\\', '"'), array('\\\\', '\\"'), $value);
return '"'.$escaped.'"';
}
}
/**
* Given a an EasyRdf_Resource or URI, convert it into a string, suitable to
* be written to a Turtle document. URIs will be shortened into CURIES
* where possible.
*
* @param EasyRdf_Resource $resource The resource to convert to a Turtle string
* @param boolean $createNamespace If true, a new namespace may be created
* @return string
*/
public function serialiseResource($resource, $createNamespace = false)
{
if (is_object($resource)) {
if ($resource->isBNode()) {
return $resource->getUri();
}
$resource = $resource->getUri();
}
$short = EasyRdf_Namespace::shorten($resource, $createNamespace);
if ($short) {
$this->addPrefix($short);
return $short;
}
return self::escapeIri($resource);
}
/**
* Given an EasyRdf_Literal object, convert it into a string, suitable to
* be written to a Turtle document. Supports multiline literals and literals with
* datatypes or languages.
*
* @param EasyRdf_Literal $literal
* @return string
*/
public function serialiseLiteral($literal)
{
$value = strval($literal);
$quoted = self::quotedString($value);
if ($datatype = $literal->getDatatypeUri()) {
if ($datatype == 'http://www.w3.org/2001/XMLSchema#integer') {
return sprintf('%d', $value);
} elseif ($datatype == 'http://www.w3.org/2001/XMLSchema#decimal') {
return sprintf('%s', $value);
} elseif ($datatype == 'http://www.w3.org/2001/XMLSchema#double') {
return sprintf('%e', $value);
} elseif ($datatype == 'http://www.w3.org/2001/XMLSchema#boolean') {
return sprintf('%s', $value);
} else {
$escaped = $this->serialiseResource($datatype, true);
return sprintf('%s^^%s', $quoted, $escaped);
}
} elseif ($lang = $literal->getLang()) {
return $quoted . '@' . $lang;
} else {
return $quoted;
}
}
/**
* Convert an EasyRdf object into a string suitable to
* be written to a Turtle document.
*
* @param EasyRdf_Resource|EasyRdf_Literal $object
* @return string
*/
public function serialiseObject($object)
{
if ($object instanceof EasyRdf_Resource) {
return $this->serialiseResource($object);
} elseif ($object instanceof EasyRdf_Literal) {
return $this->serialiseLiteral($object);
} else {
throw new InvalidArgumentException(
"serialiseObject() requires \$object to be ".
"of type EasyRdf_Resource or EasyRdf_Literal"
);
}
}
/**
* Protected method to serialise a RDF collection
* @ignore
*/
protected function serialiseCollection($node, $indent)
{
$turtle = '(';
$count = 0;
while ($node) {
if ($id = $node->getBNodeId()) {
$this->outputtedBnodes[$id] = true;
}
$value = $node->get('rdf:first');
$node = $node->get('rdf:rest');
if ($node and $node->hasProperty('rdf:first')) {
$count++;
}
if ($value !== null) {
$serialised = $this->serialiseObject($value);
if ($count) {
$turtle .= "\n$indent $serialised";
} else {
$turtle .= " ".$serialised;
}
}
}
if ($count) {
$turtle .= "\n$indent)";
} else {
$turtle .= " )";
}
return $turtle;
}
/**
* Protected method to serialise the properties of a resource
* @ignore
*/
protected function serialiseProperties($res, $depth = 1)
{
$properties = $res->propertyUris();
$indent = str_repeat(' ', ($depth*2)-1);
$turtle = '';
if (count($properties) > 1) {
$turtle .= "\n$indent";
}
$pCount = 0;
foreach ($properties as $property) {
if ($property === 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type') {
$pStr = 'a';
} else {
$pStr = $this->serialiseResource($property, true);
}
if ($pCount) {
$turtle .= " ;\n$indent";
}
$turtle .= ' ' . $pStr;
$oCount = 0;
foreach ($res->all("<$property>") as $object) {
if ($oCount) {
$turtle .= ',';
}
if ($object instanceof EasyRdf_Collection) {
$turtle .= ' ' . $this->serialiseCollection($object, $indent);
} elseif ($object instanceof EasyRdf_Resource and $object->isBNode()) {
$id = $object->getBNodeId();
$rpcount = $this->reversePropertyCount($object);
if ($rpcount <= 1 and !isset($this->outputtedBnodes[$id])) {
// Nested unlabelled Blank Node
$this->outputtedBnodes[$id] = true;
$turtle .= ' [';
$turtle .= $this->serialiseProperties($object, $depth+1);
$turtle .= ' ]';
} else {
// Multiple properties pointing to this blank node
$turtle .= ' ' . $this->serialiseObject($object);
}
} else {
$turtle .= ' ' . $this->serialiseObject($object);
}
$oCount++;
}
$pCount++;
}
if ($depth == 1) {
$turtle .= " .";
if ($pCount > 1) {
$turtle .= "\n";
}
} elseif ($pCount > 1) {
$turtle .= "\n" . str_repeat(' ', (($depth-1)*2)-1);
}
return $turtle;
}
/**
* @ignore
*/
protected function serialisePrefixes()
{
$turtle = '';
foreach ($this->prefixes as $prefix => $count) {
$url = EasyRdf_Namespace::get($prefix);
$turtle .= "@prefix $prefix: <$url> .\n";
}
return $turtle;
}
/**
* @ignore
*/
protected function serialiseSubjects(EasyRdf_Graph $graph, $filterType)
{
$turtle = '';
foreach ($graph->resources() as $resource) {
/** @var $resource EasyRdf_Resource */
// If the resource has no properties - don't serialise it
$properties = $resource->propertyUris();
if (count($properties) == 0) {
continue;
}
// Is this node of the right type?
$thisType = $resource->isBNode() ? 'bnode' : 'uri';
if ($thisType != $filterType) {
continue;
}
if ($thisType == 'bnode') {
$id = $resource->getBNodeId();
if (isset($this->outputtedBnodes[$id])) {
// Already been serialised
continue;
}
$this->outputtedBnodes[$id] = true;
$rpcount = $this->reversePropertyCount($resource);
if ($rpcount == 0) {
$turtle .= '[]';
} else {
$turtle .= $this->serialiseResource($resource);
}
} else {
$turtle .= $this->serialiseResource($resource);
}
$turtle .= $this->serialiseProperties($resource);
$turtle .= "\n";
}
return $turtle;
}
/**
* Serialise an EasyRdf_Graph to Turtle.
*
* @param EasyRdf_Graph $graph An EasyRdf_Graph object.
* @param string $format The name of the format to convert to.
* @param array $options
* @throws EasyRdf_Exception
* @return string The RDF in the new desired format.
*/
public function serialise($graph, $format, array $options = array())
{
parent::checkSerialiseParams($graph, $format);
if ($format != 'turtle' and $format != 'n3') {
throw new EasyRdf_Exception(
"EasyRdf_Serialiser_Turtle does not support: $format"
);
}
$this->prefixes = array();
$this->outputtedBnodes = array();
$turtle = '';
$turtle .= $this->serialiseSubjects($graph, 'uri');
$turtle .= $this->serialiseSubjects($graph, 'bnode');
if (count($this->prefixes)) {
return $this->serialisePrefixes() . "\n" . $turtle;
} else {
return $turtle;
}
}
}