英文:
Use-case diagram: When to decompose use-case and when not to?
问题
-
例如，假设我想为一个类似的人工自动售货机绘制用例图，如下所示：
-
自动售货机有3个选项：
碳酸饮料、茶和纯净水。 -
用户只能选择上述其中一种进行订购：
- 如果用户选择
碳酸饮料，则用户需要选择品牌，例如可口可乐或百事可乐。 - 否则，如果用户选择
茶，则需要选择糖的数量。 - 或者如果用户选择
纯净水，那就是全部了。
- 如果用户选择
-
在选择饮料之后，用户还必须选择饮料的数量（有点牵强）。然后，机器会发送确认消息供用户确认。
我尝试过这个，但不太确定，不知道要保留什么，要添加什么或删除什么。。
问题如下：
-
这里的“选择饮料数量”和“确认”应该作为独立的用例保留，还是应该与总体用例“购买一种饮料”合并？
-
如果至少要保留其中一个，它们应该被绘制为“购买一种饮料”的包含用例，还是应该绘制为独立的用例？
-
我考虑将3个用例“购买碳酸饮料”、“购买茶”、“购买纯净水”看作是“购买一种饮料”的离散化。对于“购买碳酸饮料”和“购买茶”，我是否应该保留包含用例：“选择品牌”和“选择糖的数量”，还是应该将它们删除？
-
更一般的问题：在什么情况下，执行某个大用例的步骤应该保留为用例，什么情况下不应该？ 这里有很多类似的问题，但答案不一致。
英文:
For an example, say, I want to draw a use-case diagram for an artificial vending machine like so:
-
The vending machine have 3 options:
carbonated drinks,tea, andpure water. -
The user can choose only 1 of the above for an order:
- If the user chooses
carbonated drinks, the user needs to choose which brand: say Coke or Pepsi. - Else if the user chooses
tea, then he/she have to choose the amount of sugar. - Else if the user chooses
pure water, then that's it.
- If the user chooses
-
After choosing the drinks, the user then has to choose the number of drinks (a little bit contrived). The machine then sends out a confirmation message for the user to confirm.
I tried this but not really sure of it, don't know what to keep, what to add or what to remove..
The questions are:
-
Should the 2
Choose the number of drinksandConfirmhere be kept independently as use-cases, or should they be merge with the grand use-case:Buy a kind of drink? -
If at least 1 of them is to be kept, should I draw them as including use-case of
Buy a kind of drinkor should they be drawn as independent use-cases? -
The 3 use-cases
Buy carbonated,Buy tea,Buy pure waterI considered as the discretization ofBuy a kind of drink. ForBuy carbonatedandBuy tea, should I keep the including use-cases:Choose brandandChoose sugar amountor should I remove them also? -
More general question: When should a step of doing some big use-case should be kept as a use-case, and when shouldn't? There are a lot of questions on here that are the same, but the answers are non-consistent.
答案1
得分: 1
使用案例关注的是“是什么”，而不是“如何”。后者涉及到活动，并分为行动。用例只展示了一个正在考虑的系统为其参与者带来的附加值。
因此，唯一的附加值是“销售饮料”，仅此而已。
我建议阅读Bittner/Spence关于用例的内容。他们称之为“综合”，这是正确的词汇。不是分析，更不是分解。
奇怪的是，技术人员总是想要分解事物。嗯，我知道学习起来很困难，因为我也曾困惑不解。这可能是因为它涉及到简单性。
英文:
Use cases are about the what and not about the how. The latter goes into Activity and is split to Actions. Use case only show the added value a system under consideration brings to its actors.
So the only added value is Sell drinkand that's it.
I recommend reading Bittner/Spence about use cases. They call it synthesis and that's the right word. Not analysis and even less decomposition.
Strange, that techies always want to decompose things. Well, I know it's hard to learn since I had been scratching my head too. It's probably so complicated because its about simplicity.
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