Artifacts > Requirements Artifact Set > Use-Case Model... > Use-Case Package
The following people use the use-case packages:
Use-case package partitioning is done as soon as the use-case model is too large to maintain as a flat structure. This can be the case early in inception, or later on in the elaboration or construction phases.
A requirements specifier is responsible for the integrity of the package, which ensures that:
It is recommended that the requirements specifier responsible for a use-case package is also responsible for its contained use cases. For more information, refer to Guidelines: Use Case.
+ 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.
Rational Unified Process