Use Case Diagrams

The first diagram to look at is the Use Case diagram. The main ingredients for this type of diagram are use cases and actors, together they define the roles that users can play within a system. They are associated to the tasks, or use cases, they are involved in. It is often used in early stages of the design process to collect the intention requirements of a project.

If you are not well-acquainted with UML yet, remember that a use case is not just a bubble noted in the diagram. Along with this bubble, there should be a description of the use case, a typical scenario, exceptional cases, preconditions etc. These can either be expressed in external texts using regular text processing tools, requirements tools or file cards. It can be and is often refined using other diagrams like a sequence diagram or an activity diagram that explain its main scenarios. The basic description of a use case can also be inserted in the Documentation tab of the Details pane.

Figure 10-4. A Use Case diagram.

Extension points can be added to a use case via the extension point button in the Details pane or via the extension point rapid button.

Diagram Elements

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Use Case

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