53 ).
FIGURE 2-51
Use case relationships.
uc [package] Car usage [secondary use cases]
End car usage
Show car usage
Determine car
usage data
?«include?» ?«include?»
FIGURE 2-52
Use cases for ??? route. ???
uc [package] Routes
Add route
Modify route Delete route
Essence
Select route
Modify route
Confirm change
Essence
Select route
Delete route
Confirm deletion
Essence
Add route
Compute route
Display route
87
The use case generalization is meaningful only provided that the relationship
can be read in the direction of the arrow to say: ??? use case is like use
case , ??? or, in this specifi c case: ??? modify route is like edit route. ??? Sounds perfectly
alright! Though this is not a 100 percent rule it covers most cases. Moreover, the
abstract use case should be only slightly more abstract than the concrete use
cases. Otherwise, they would have to become more and more abstract in order
to always fi nd a common ??? master ??? use case for two arbitrary use cases. Grossly
exaggerating, this would mean that if we used a use case do something , we would
have found a master use case for all our use cases.
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