private static function checkDSN($dsn) {
		$dsn = trim($dsn);
		$dsn = strtolower($dsn);
		if (
					 strpos($dsn, 'mysql:')!==0
				  && strpos($dsn,'sqlite:')!==0
				  && strpos($dsn,'pgsql:')!==0
				  && strpos($dsn,'cubrid:')!==0
				  && strpos($dsn,'oracle:')!==0
		) {
			trigger_error('Unsupported DSN');
		}
		else {
			return true;
		}
	}