public function validateVocabularyUri($uri)
    {
        $uri = trim($uri);

        // If the vocabulary URI is invalid
        if (!strlen($uri) || !filter_var($uri, FILTER_VALIDATE_URL)) {
            throw new RuntimeException(
                sprintf(RuntimeException::INVALID_VOCABULARY_URI_STR, $uri),
                RuntimeException::INVALID_VOCABULARY_URI
            );
        }

        return $uri;
    }