6.6. Definition: What are Three Kinds of Actors?
An actor is anything with behavior, including the system under discussion (SuD) itself when it calls upon the services of other systems.Cockburn97]. Older definitions inconsistently excluded the SuD as an actor, even when it called upon services of other systems. All entities may play multiple roles , including the SuD.
- Primary actor
has user goals fulfilled through using services of the SuD. For example, the cashier.- Why identify? To find user goals, which drive the use cases.
- Supporting actor
provides a service (for example, information) to the SuD. The automated payment authorization service is an example. Often a computer system, but could be an organization or person.- Why identify? To clarify external interfaces and protocols.
- Offstage actor
has an interest in the behavior of the use case, but is not primary or supporting; for example, a government tax agency.- Why identify? To ensure that all necessary interests are identified and satisfied. Offstage actor interests are sometimes subtle or easy to miss unless these actors are explicitly named.