A

Modify File

User

Delete File

Figure 6-2. Example of bad selection of use cases.

Figure 6-2 shows things that the systems should do, but they are all related to only one thing the user wants the system to do: Administer a file system. According to the definition of the use cases, they describe what the system should do that will benefit at the least one of the actors. The use case Delete File may never be invoked if a file has not been added to the system. The same reasoning can be done for the use case Modify File. Events like modifying and deleting a file are useful to a user only when a file is already added to the system. Therefore, all three functions can be gathered in a sole use case named Administer Files as shown in Figure 6-3. Gathering several functions into a unique use case is a better presentation of what the system should do for the users and it focuses on the value the user will obtain from the system. Dividing the behavior of the system into small functionalities does not help to understand the conceptual model of the system.

Modify File

User

Delete File

Figure 6-2. Example of bad selection of use cases.

User

0 0

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