We proceed like this step by step. Not every use case step has to be necessarily
detailed with an activity. Two or three explanatory sentences may be
suffi cient; see, e.g., the step terminate usage start in Figure 2.59 . By the way,
this step is worth noting in another respect: It is not an essential step, but one
that was ??? discovered ??? just now. It is absolutely admissible that new steps,
which are not essential, are added on this abstraction level as we look at the
exceptions.
In the top right corner in the activity ( Figure 2.59 ) you can see a precondition
that has to be met in order for the activity to execute. Preconditions result partly
from the fact that other use cases have to have been executed beforehand. You
can also model this using system processes (Section 2.4.3).
Exceptions and detailing require a lot of domain information. This is why we
need to closely cooperate with domain experts. We have to be aware of the fact
that the activity diagrams are not as simple as use case diagrams. You should nevertheless
try to use them in discussions and workshops with stakeholders.
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