我试图在我的本地机器上运行我的项目，但它带来了以下错误：
错误号：
2
文本：PDO::__construct() [pdo.--construct]: php_network_getaddresses: getaddrinfo failed: The requested name is valid, but no data of the requested type was found. LOCATION: C:\xampp\htdocs\rsecrets\business\database_handler.php, line 25, at December 4, 2012, 12:46 pm
我如何定义连接：
define('DB_PERSISTENCY', 'true');
define('DB_SERVER', 'localhost');
define('DB_USERNAME', 'root');
define('DB_PASSWORD', '');
define('DB_DATABASE', 'xxyy');
define('PDO_DSN', 'mysql:host=' . DB_SERVER . ';dbname=' . DB_DATABASE);
这是 database_handler.php 第 25 行的内容：
self::$_mHandler =
new PDO(PDO_DSN, DB_USERNAME, DB_PASSWORD,
array(PDO::ATTR_PERSISTENT => DB_PERSISTENCY));
我没有得到什么？