Use cases are used for defining how the modeled system is to be used by its surroundings. A use case models one usage of the system; that is, it describes what sequences of actions will be performed by the system as a response to events occurring outside the system caused by the users. However, it does not capture actions outside the system; a use case exists only inside the system. A use case constitutes the complete usage of the system in the sense that it starts when someone outside the system initiates it, and it ends when, based on the initial input, no other input is expected and no more internal actions are to be performed.
In the ATM example, the
Withdraw Moneyuse case ...
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