Learning UML

Generalizations

Actors may be similar in how they use a system; for example, project managers, resource managers, and system administrators may log in and out of our project management system. Use cases may be similar in the functionality provided to users; for example, a project manager may publish a project’s status in two ways: by generating a report to a printer or by generating a web site on a project web server.

Given that there may be similarities between actors and use cases, how do we organize the use cases that define what a system should do? And how do we use the information about similarities between actors and use cases to determine how best to execute a project? Specialized types of generalizations, called actor and use case generalizations, address these questions. Generalizations are introduced and discussed in Chapter 3. The next two sections discuss these specialized types of generalizations.

Actor Generalizations

Figure 4-10 shows that project managers, resource managers, and system administrators may log in and out of the project management system. Thus, logging in and out is common to these actors. Actor generalizations address such situations by factoring out and reusing similarities between actors.

Figure 4-10. Similar actors

An actor generalization from a more specific, or specialized, actor to a more general, or generalized, actor indicates that instances of ...