An individual use case is represented by an ellipse, an actor by a stick figure, and an
association by a line between the actor and the use case. The role of the actor is written
beneath the icon. Actors are not limited to humans. If a system communicates with another
application, and expects input or delivers output, then that application can also be considered
an actor. A use case is typically represented by a verb followed by an object, such
as View property, Lease property. An example use case diagram for Client with four use
cases is shown in Figure 25.17(a) and a use case diagram for Staff in Figure 25.17(b). The
use case notation is simple and therefore is a very good vehicle for communication.