前几个月过于疲劳，干脆这个月请假在家休息，顺便看看书。
打开闲置好久的QQ，看看有没有什么留言，结果正赶上一个家伙病急乱投医，找我问需求用例怎样写。
好久不搞开发，也忘得差不多了，就找了份以前的参考文档传过去，一会儿收到回复，说其他都明白了，就是“后置条件”没整清楚，参考文档中在这一行只有尖括号中一句话：用例执行后为真的状态。这个描述是过于简单了点。
刚好前天整理图书，翻出一本《Managing Software Reqirement – A Use Case Approach 2th》，找出书，跳到Chapter 21，找到Identifying the Pre- and Post-conditions一节
这里的解释稍微详细点：Post-conditions are the states the system can be in after the use case ends，另有一句：such as system state or persistent data that is left when the use case is complete
即后置条件描述的是用例结束时的系统状态或持久数据。（会影响到执行其他用例）
书中举了个电灯开关的例子：
Post-condition for the Control Light Use Case
● On leaving this use case, the system remembers the current brightness level for the selected On/Off/Dim button
即当控制灯亮度这个用例结束时，系统应根据所按按钮记住当前的亮度级别（否则下次再按，就无法知道灯应该关还是开还是暗一点了），例子很浅显易懂，比画一堆UML符号更容易让人理解。
(还可以举个设计键盘的例子，比如按下某个键之后，该键应在放手后自动弹起–否则卖不出去的)
这一章中还有一段：
A post-condition for a use case should be true regardless of which alternative flows were executed; it should not be true only for the main flow. If something could fail, you would cover that in the post-condition by saying “The action is completed, or if something failed, the action is not performed,” rather than just “The action is completed.”
即后置条件应该包括用例所有备选流结束后可能的状态（成功或错误的状态）。
书中对这一点好像没有相关例子说明(我没认真全看，走马观花)。
临时想了个”空气开关”当例子来忽悠：当正常按下后，开关应不会弹起，但是当有异常发生(设备短路)时，这个操作就不能正常完成，系统的状态会有点不同(开关自动弹起，电路断开)。
或者用刚才那个键盘的例子；如果所按的键不是a-z之类，而是按下Caps Lock后，系统为大写锁定状态。
那哥们过了半天，回复了一个字：哦
但愿他没被绕迷糊吧。
这个太专业了
很难懂
图迷吧装修效果图 —— 2011年09月23日 @10:25 am
呵呵 路过 瞧瞧
金车色 —— 2011年09月23日 @11:54 am
为何总要加点英文，搞得人稀里糊涂
美女图片 —— 2011年09月24日 @9:56 am
搞得人稀里糊涂
ugg boots —— 2011年10月11日 @12:34 am
博主好像很久都没更新日记了，估计这段时间很忙，没空
内裤反着穿 —— 2011年11月15日 @3:01 pm
专业性滴东西，搞不懂撒~~~
东篱桃源 —— 2011年11月29日 @11:42 am
你好Everything you said is what I need!
UGGs —— 2011年12月29日 @2:34 pm
这个太专业了
知识问答 —— 2012年02月08日 @3:28 pm
你好啊
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