A use case which does nothing?

Question

Am I allowed to make a use case which "does nothing"? For example, consider a soda vending machine: it can vend a can of soda or a cup of soda.

So my top level use case is "buy soda". The extending use cases are "buy can of soda" and "buy a cup of soda". Can I make "buy soda" blank, i.e. it has no steps?

Do you expect the requirements police coming and arrest you? — Stefan Steinegger, Feb 18 '13 at 10:45
I think that the question is clear enough, otherwise the OP would not have accepted my answer. Perhaps the ambiguity was because the question was about "child use cases", which is not the exact term. In other words the question is: can an extended use case be empty? — Javier, Feb 20 '13 at 05:27

score 1 · Accepted Answer · answered Feb 18 '13 at 05:33

No, because "buy can of soda" and "buy a cup of soda" are extending use cases, and the extend relationship requires at least one ExtensionPoint from the extended use case. (UML Superstructure v2.4.1 section 16.3.3). An extension point is a reference to a location within a use case at which parts of the behavior of other use cases may be inserted (section 16.3.4).

In other words, you have to specify how and when the behaviors defined in "buy can of soda" and "buy a cup of soda" can be inserted into the behavior defined in "buy soda".

There is a similar example in the standard (Fig 16.3), which I adapted to your use cases. See: http://tinypic.com/r/huisg3/6

btw, can you also help me with this one - http://stackoverflow.com/questions/14929363/use-case-diagram-for-overriding-settings — FirstName LastName, Feb 18 '13 at 07:41

A use case which does nothing?

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