public static function getInstance()
 {
     if (is_null(self::$instance)) {
         self::$instance = new self();
     }
     return self::$instance;
 }
 public function updateData(SMWSemanticData $data, $store)
 {
     //get list of properties which are set by this article
     //todo: think about only querying for modified properties
     $properties = $data->getProperties();
     foreach ($properties as $name => $property) {
         //ignore internal properties
         if (!$property->isUserDefined() || $name == QRC_HQID_LABEL) {
             unset($properties[$name]);
         }
     }
     //determine differences between the new and the original semantic data
     global $wgTitle;
     if ($wgTitle) {
         $originalData = $store->getSemanticData($wgTitle);
         foreach ($originalData->getProperties() as $oName => $oProperty) {
             if (array_key_exists($oName, $properties)) {
                 $oValues = $originalData->getPropertyValues($oProperty);
                 $values = $data->getPropertyValues($properties[$oName]);
                 if (count($oValues) == count($values)) {
                     $oWikiValues = array();
                     foreach ($oValues as $key => $value) {
                         $oWikiValues[$value->getWikiValue()] = true;
                     }
                     $wikiValues = array();
                     foreach ($values as $key => $value) {
                         $wikiValues[$value->getWikiValue()] = true;
                     }
                     $unset = true;
                     foreach (array_keys($values) as $value) {
                         if (!array_key_exists($value, $oWikiValues)) {
                             $unset = false;
                             break;
                         }
                     }
                     if ($unset) {
                         unset($properties[$oName]);
                     }
                 }
                 //echo('<pre>'.print_r($oProperty, true).'</pre>');
                 //echo('<pre>'.print_r(, true).'</pre>');
             } else {
                 if ($oProperty->isUserDefined() && $name != QRC_HQID_LABEL) {
                     $properties[$oName] = $oProperty;
                 }
             }
         }
     }
     //deal with categories and determine which queries to update
     $categories = array();
     global $wgParser;
     if ($wgParser && $wgParser->getOutput() && $wgTitle) {
         $categories = $wgParser->getOutput()->getCategories();
         $originalCategories = $wgTitle->getParentCategories();
         //echo('<pre>'.print_r($originalCategories, true).'</pre>');
         foreach (array_keys($originalCategories) as $category) {
             $category = substr($category, strpos($category, ':') + 1);
             if (array_key_exists($category, $categories)) {
                 unset($categories[$category]);
             } else {
                 $categories[$category] = true;
             }
         }
     }
     //echo('<pre>'.print_r(array_keys($categories), true).'</pre>');
     //echo('<pre>'.print_r(array_keys($properties), true).'</pre>');
     if (count($properties) > 0 || count($categories) > 0) {
         //query for all articles that use a query which depends on one of the properties
         $queryString = SMWQRCQueryManagementHandler::getInstance()->getSearchQueriesAffectedByDataModification(array_keys($properties), array_keys($categories));
         SMWQueryProcessor::processFunctionParams(array($queryString), $queryString, $params, $printouts);
         $query = SMWQueryProcessor::createQuery($queryString, $params);
         $queryResults = $this->getQueryResult($query, true, false)->getResults();
         //get query ids which have to be invalidated
         $queryIds = array();
         foreach ($queryResults as $queryResult) {
             $semanticData = $store->getSemanticData($queryResult);
             $invalidatePC = false;
             $tQueryIds = SMWQRCQueryManagementHandler::getInstance()->getIdsOfQueriesUsingProperty($semanticData, $properties);
             if (count($tQueryIds) > 0) {
                 $invalidatePC = true;
             }
             $queryIds = array_merge($queryIds, $tQueryIds);
             $tQueryIds = SMWQRCQueryManagementHandler::getInstance()->getIdsOfQueriesUsingCategory($semanticData, $categories);
             if (count($tQueryIds) > 0) {
                 $invalidatePC = true;
             }
             $queryIds = array_merge($queryIds, $tQueryIds);
             global $invalidateParserCache, $showInvalidatedCacheEntries;
             if ($invalidatePC && $invalidateParserCache && !$showInvalidatedCacheEntries) {
                 $title = $queryResult->getTitle();
                 $title->invalidateCache();
             }
         }
         $qrcStore = SMWQRCStore::getInstance()->getDB();
         $qrcStore->invalidateQueryData($queryIds);
     }
     return $store->doUpdateData($data);
 }