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4, the action itself does not have a stereotype ?«essential
?», while the invoked activity does. The stereotype of the activity is also represented in pertaining
call actions.
91
We try to fi nd possible exceptions and variants for each single action. We can
often distinguish between successful and unsuccessful results after each action.
Let ??™ s look at the fi rst step, identify customer . The result can be either customer
identifi ed or customer not identifi ed ( Figure 2.57 ). The former result corresponds
to the standard fl ow, while the latter requires more thinking. We ask the domain
experts and learn that the system should terminate in such a case. If a customer
cannot be identifi ed, they shouldn ??™ t be able to access the car. Accordingly there is
no fl ow variant where no customer has to be identifi ed.
A fl ow can take different turns based on a decision. We use a decision node
to model this in the activity diagram. The notation is a diamond with one incoming
fl ow and an arbitrary number of outgoing fl ows, each fi tted with a condition.


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