A model structured into smaller units is easier to understand. It is easier to show relationships among the
model's main parts if you can express them in terms of packages. A package is either the top-level package
of the model, or stereotyped as a use-case package. You can also let the customer decide how to
structure the main parts of the model.
-
If there are many use cases or actors, you can use use-case packages to further structure the use-case
model. A use-case package contains a number of actors, use cases, their relationships, and other
packages; thus, you can have multiple levels of use-case packages (packages within packages).
-
The top-level package contains all top-level use-case packages, all top-level actors, and all top-level
use cases.
You can partition a use-case model into use-case packages for many reasons:
-
You can use use-case packages to reflect order, configuration, or delivery units in the finished
system.
-
Allocation of resources and the competence of different development teams may require that the project
be divided among different groups at different sites. Some use-case packages are suitable for a group,
and some for one person, which makes packages a naturally efficient way to proceed with development.
You must be sure, however, to define distinct responsibilities for each package so that development can
be performed in parallel.
-
You can use use-case packages to structure the use-case model in a way that reflects the user types.
Many change requirements originate from users. Use-case packages ensure that changes from a particular
user type will affect only the parts of the system that correspond to that user type.
-
In some applications, certain information should be accessible to only a few people. Use-case packages
let you preserve secrecy in areas where it is needed.
|