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Object-Oriented Analysis and Design 345

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the customer asks for $300, a legal amount to withdraw at this

time. The machine dispenses $300 and prints a receipt, and the

customer takes the money and the receipt.

Postconditions: Customer account is debited $300, and customer has $300 cash.

This use case can be shown with the incredibly simple diagram given in Figure 11.9.

FIGURE11.9
Use-case diagram.

Withdraw Cash

Association

Customer

Actor Use Case

Little information is captured here except a high-level abstraction of an interaction

between an actor (the customer) and the system. This diagram becomes slightly more

useful when you show the interaction among use cases. I say only slightlymore useful

because only two interactions are possible:<<uses>>and <<extends>>. The <<uses>>

stereotype indicates that one use case is a superset of another. For example, it isn’t possi-

ble to withdraw cashwithout first logging in. This relationship can be shown with the

diagram in Figure 11.10.

FIGURE11.10
The <>
stereotype. Withdraw Cash

Customer

Log in

<<Uses>>

Figure 11.10 indicates that the Withdraw Cash use case “uses” the Log In use case, and,

thus, Log In is a part of Withdraw Cash.