public function getDataType($key)
    {
        // check for existing datatype, and raise an exception
        // if it doesn't exist. Usefull when new data type defined
        // in the new version of MySQL Workbench
        if (isset($this->dataTypes[$key])) {
            return $this->dataTypes[$key];
        } elseif (isset($this->userDatatypes[$key])) {
            return $this->userDatatypes[$key];
        } else {
            throw new \RuntimeException(sprintf('Unknown data type "%s".', $key));
        }
    }