Chapter 5. Modeling the System Environment

Actor: An External User

This chapter examines the other parts of a use-case model—that is, the actors of the system and the associations between the actors and the use cases. An actor models a role that is played by a user of the system when utilizing the system—that is, when the user interacts with use cases (see Figure 5.1). Because the actors are played by the users of the system, all the actors appear outside the system being modeled. As we are modeling the system, the role of an actor is defined from the system's point of view—the actors model how the system perceives its environment.

A system perceives its users as playing different roles toward the system. All persons who withdraw money using an ATM act as ATM Customers toward the ATM, whereas one user category of a Sales Management System is represented by an actor called Sales Manager.

Figure 5.1. A system ...

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