/*驱动接口*/
interface db_driver {
        function connect();
    function query();
}

/*mysql的数据库实现*/
class db_mysql implements db_driver {
    
    public function connect() {
        /*具体代码实现*/
    }
    
    function query($sql) {
                /*具体代码实现*/
    }
}
/*pdo的数据库实现*/
class db_pdo implements db_driver {
    
    public function connect() {
        /*具体代码实现*/
    }
    
    function query($sql) {
                /*具体代码实现*/
    }
}
/*定义适配器类*/
class db_adapter {

    private $db;
    
    function __construct($db_obj) {
        $this->db = $db_obj;
    }
    
    function connect() {
        $this->db->connect();
    }
    
    function query($sql) {
        $this->db->query($sql);
    }
}
/*客户端应用*/
$db = new db_adapter(new db_mysql());