/**
* Generates and makes a query into a external vocabulary for an exact
* match for a particular concept.
* @param Vocabulary $exvoc external vocabulary to query
* @param string $exuri resource URI
* @param string $lang language of label to query for
* @return string label, or null if not found in vocabulary
*/
protected function getExternalLabel($exvoc, $exuri, $lang)
{
if ($exvoc) {
$exsparql = $exvoc->getSparql();
$results = $exsparql->queryLabel($exuri, $lang);
return isset($results[$lang]) ? $results[$lang] : null;
} else {
return null;
}
}
