static public function create ($driver, array $settings, array $optionsOverride = null)
  {
    switch ($driver) {
      case 'mysql':
        return new MysqlExtPDO ($settings, $optionsOverride);
      case 'pgsql':
        return new PostgreSqlExtPDO ($settings, $optionsOverride);
      case 'sqlite':
        return new SqliteExtPDO ($settings, $optionsOverride);
      case 'sqlsrv':
        return new SqlserverExtPDO ($settings, $optionsOverride);
    }
    throw new \RuntimeException ("Unsupported driver: $driver");
  }