public function execute( $query ) {
		if ( $query instanceof QueryBuilder ) {
			$query = $query->getSPARQL();
		}

		if ( !is_string( $query ) ) {
			throw new InvalidArgumentException( '$query has to be a string or an instance of QueryBuilder' );
		}

		$result = $this->getResult( $query );
		
		// TODO also support ask queries (with key 'boolean')
		//      https://www.w3.org/TR/rdf-sparql-json-res/
		return $result['results'];
	}