事务脚本模式是什么意思？

/*事务脚本模式: 类似于thinkphp中的model层，或者说就是操作数据库的类。
个人觉得实践中使用起来还是挺简单方便的，就是SQL语句写死了的话，灵活性就不够。
示例代码如下：*/namespace woo\process;abstract class Base{static $DB;                 //pdo对象static $stmts = array(); //sql语句句柄function __construct (){$dsn = \woo\base\ApplicationRegistry::getDSN();if(is_null($dsn)){throw new \woo\base\AppException("No DSN");
        }
        self::$DB = new PDO($dsn);
        self::$DB->setAttribute(\PDO::ATTR_ERRMODE,\PDO::ERRMODE_EXCEPTION);
    }    function prepareStatement($stmt_s){   //缓存sql语句句柄if(isset(self::$stmts($stmt_s)){return self::$stmts[$stmt_s];
        }$stmt_handle = self::$DB->prepare($stmt_s);
        self::$stmts[$stmt_s] = $stmt_handle;return $stmt_handle;
    }    protected function doStatement($stmt_s,$values_a){    //执行sql并获取一个语句资源$sth = $this->prepareStatement($stmt_s);$sth->closeCursor();$db_result = $sth->execute($values_a);return $sth;
    }
}//这个类就是向数据库中写入一些数据，比较简单没什么好多说的class VenueManager extends Base{static $add_venue = "INSERT INTO venue (name) values(?)";static $add_space = "INSERT INTO space (name,venue) values(?,?)";static $check_slot = "SELECT id,name FROM event WHERE space = ? AND (start+duration)>? AND start doStatement(self::$add_venue,$ret['venue']);$v_id = self::$DB->lastInsertId();$ret['spaces'] = array();foreach($space_array as $space_name){$values = array($space_name,$v_id);$this->doStatement(self::$add_space,$values);$s_id = self::$DB->lastInsertId();array_unshift($values,$s_id);$ret['spaces'][] = $values;
        }return $ret;
    }    function bookEvent ($space_id,$name,$time,$duration){$values = array($space_id,$time,($time+$duration));$stmt = $this->doStatement(self::$check_slot,$values,false);if($result = $stmt->fetch()){throw new \woo\base\AppException("double booked! try again");
        }$this->doStatement(self::$add_event,array($name,$space_id,$time,$duration));
    }
}//客户端,使用起来还是比较简便的$venue =  new VenueManager();$venue->addVenue('test',array('test1','test2','test3'));