| UML Representation: Package in the use-case model, either its top-level package, or stereotyped as <<use-case
package>>
+ Provide a hierarchical model structure with separate functional units. This is easier to understand than a
flat model structure (without packages) if the use-case model and the system is relatively large.
+ Offer a good opportunity to distribute work and responsibilities among several developers according to their
area of competence. This is particularly important when you are building a large system. Use-case packages also offer a
secure basis if you need to ensure confidentiality among your developers so that only a few know about the complete
functionality of the system.
+ Because use-case packages should be units of high cohesion, changing one package will not affect other
packages.
- Maintaining use-case packages means more work for the use-case modeling team.
- Using use-case packages means that there is yet another notational concept for the developers to learn.
If you use this technique you have to decide how many levels of packages to use. A rule of thumb is that each use-case
package should contain approximately 3 to 10 smaller units (use cases, actors, or other packages). The table below
gives some suggestions as to how many packages you should use given the number of use cases and actors. The quantities
overlap because it is impossible to give exact guidelines.
-
0-15: No use-case packages needed.
-
10-50: Use one level of use-case packages.
-
> 25: Use two levels of use-case packages.
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