public function determineObjectDatatype($objectString)
    {
        $datatype = null;

        // checks if ^^< is in $objectString
        $arrowPos = strpos($objectString, '"^^<');

        // checks if $objectString starts with " and contains "^^<
        if ('"' === substr($objectString, 0, 1) && false !== $arrowPos) {
            // extract datatype URI
            $datatype = substr($objectString, $arrowPos + 4);

            return substr($datatype, 0, strlen($datatype) - 1);

        // checks for surrounding ", without ^^<
        } elseif ('"' == substr($objectString, 0, 1)
            && '"' == substr($objectString, strlen($objectString) - 1, 1)) {
            // if we land here, there are surrounding quotation marks, but no datatype
            return 'http://www.w3.org/2001/XMLSchema#string';

        // malformed string, return null as datatype
        } else {
            return null;
        }
    }