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The structures required for all of these are secondary for now. It is a ??? side
product ??? that emerges when we describe and realize the services.
By way of example, we will briefl y look at another system: a soft drinks vending
machine. What does the actor customer want of this system ( Figure 2.32 )?
They are not interested in the structures of the system, but in the services only.
They want to buy a soft drink .
The services a system offers, i.e., its functionality, are described in UML by
means of use cases. A use case is denoted as an ellipse, and the actors participating
in the use case are connected to the ellipse by solid lines ( Figure 2.32 ).
A use case has always at least one actor; it is started by a domain trigger, and it
ends with a domain result. The fl ow between the trigger and the result has a time
coherence, i.e., no domain interruption is possible.
The metaphor of a ??? service provider ??? is helpful to ensure that we won ??™ t lose
sight of the important things. The system exists to render services to others.


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