public function isClass()
    {
        $returnValue = (bool) false;
        if (count($this->getPropertyValues($this->getProperty(OntologyRdfs::RDFS_SUBCLASSOF))) > 0) {
        	$returnValue = true;
        } else {
	        foreach($this->getTypes() as $type){
	        	if($type->getUri() == OntologyRdfs::RDFS_CLASS){
	        		$returnValue = true;
	        		break;
	        	}
	        }
        }
        return (bool) $returnValue;
    }