Use Cases: Patterns and Blueprints

Chapter 12. Actor Generalization: Overlapping Roles

Frequently, multiple actors have associations with the same use case. For example, in the ATM example, both the ATM Customer and the Bank System are associated with the Withdraw Money use case. From the use case's point of view, it is clear that there are two external entities interacting with it—these two entities play different roles toward the use case (see Figure 12.1).

Figure 12.1. A use case can have associations with more than one actor.

If only one external user is involved in the usage, however, only one actor is to be associated with the use case. Therefore, as soon as actors overlap—that ...