This is only one use case fragment, a so-called
secondary use case . We use the include relationship to embed it in the primary
use cases.
We fi nd only one common step in the package car usage . We need to determine
the usage data for two reasons: fi rst, for continuous usage data display, and
second, when the car usage ends to be able to forward the data to the billing system
( Figure 2.51 ).
We need to be careful not to model routinely every step that occurs more than
once as a secondary use case. Bear in mind the triple heuristic, which says that
one thinks about resolving a redundancy only in its third occurrence. If so, we
wouldn ??™ t have had to defi ne the secondary use case determine car usage data .
On the other hand, heuristics don ??™ t apply routinely either. We have to weigh each
concrete case to fi nd out what is more valuable: either no redundancy or redundancy
with the benefi t of having a less complex model, since we omit another
model element and its relationships.
If you search your use cases for common things you may fi nd that some use
cases are pretty much alike.
Pages:
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205