Not necessarily in the number of common steps, but
in the fl ows themselves. The use cases of our system ??™ s navigation system are a
good example: A customer can defi ne a new route, or change or delete an existing
route. This means that we found three use cases: add route , modify route , and
delete route ( Figure 2.52 ).
2.4 Modeling Use Cases
14 This would violate the use case criteria of the SYSMOD approach and not the formal SysML
criteria, which would be illegal.
86 CHAPTER 2 The Pragmatic SYSMOD Approach
Two use cases, modify route and delete route , are very similar. Nevertheless
it is necessary to list both use cases, because they concern two different system
services. You can document their similarity in another use case. The two fl ows will
become identical if you move one abstraction level up.
The abstract fl ow is described by an abstract use case. SysML lets you denote
the property abstract by writing its name in italics and optionally adding the word
{ abstract }. The relationship to the concrete use cases is a generalization, which is
denoted by an arrow with a solid line and closed arrowhead ( Figure 2.
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