I have this diagram. The staff receives an email when his letter is approved. Do I need add an include relationship between two use cases? If I did that, it means the staff needs to approve letter to receive an email. It's different from the description.
Definitely not. The simple reason is, that Receive Email is no use case. It is a pure function, likely used in some yet unknown use case. A use case brings added value to its actor. And receiving an email has no added value (like the dreaded Login).
It's hard to judge whether Approve Letter is a valid use case. It seems like a bit trivial. Probably if it's a certain letter in a certain process. As such, I would not let it go through as use case.
As always I recommend to read Bittner/Spence about use case modeling.
