Learning UML

Use Cases

As discussed in Chapter 2, a use case is a functional requirement that is described from the perspective of the users of a system. For example, functional requirements for the project management system include: security functionality (such as allowing users to log in and out of the system), inputting of data, processing of data, generation of reports, and so forth.

Use cases follow the type-instance dichotomy first discussed in Chapter 2 and applied to classes and object in Chapter 3. You can use the UML to talk about classes of use cases, and you can use the UML to talk about specific use cases of a class. When speaking of a class of use cases, it’s customary to use the term use case or use-case class. Thus, while you might think of a use case as a specific thing, in the UML, a use case really represents a class of things. When speaking of a specific use case of a class, use the term use-case instance.

A use case defines a functional requirement that is described as a sequence of steps, which include actions performed by a system and interactions between the system and actors. Use cases address the question of how actors interact with a system, and describe the actions the system performs.

In the UML, a use case is shown as an ellipse and labeled with the name of the use-case class. Use cases may be enclosed by a rectangle that represents the boundary of the system that provides the functionality. Figure 4-3 shows various use cases associated with the project management ...