private function _constructPdoDsn(array $params)
    {
        $dsn = 'ibm:';
        if (isset($params['host'])) {
            $dsn .= 'HOSTNAME=' . $params['host'] . ';';
        }
        if (isset($params['port'])) {
            $dsn .= 'PORT=' . $params['port'] . ';';
        }
        $dsn .= 'PROTOCOL=TCPIP;';
        if (isset($params['dbname'])) {
            $dsn .= 'DATABASE=' . $params['dbname'] . ';';
        }

        return $dsn;
    }