Use case diagrams assist in the analysis phase
of a project. They capture hard and firm constraints at a high level.
As
design decisions are made, you further decompose use-case diagrams
to create more possible use cases and scenarios, or sequences, that
implement the use case. Each use case has a folder in the browser
containing some of its possible sequences.
About this task
Scenarios describe not only the main path
through a use case, but can also include background environmental
and situational descriptions to set the stage for future events. In
other words, they can provide detailed definitions of preconditions
for a use case. Therefore, a sequence describes the main path through
a use case, whereas a variant, represented by a child use case, describes
alternate paths.
Procedure
For example, consider a VCR. One sequence of the InstallationAndSetup
use case might be the following steps:
- Add the VCR and accessories.
- Insert batteries in the remote control.
- Connect the antenna or cable system to the
VCR.
- Set the CH3/CH4 switch.
- Turn on the VCR and select an active channel.
- Learn to use the TV/VCR button.
- Test the VCR connections.
Results
The specific sequence of steps through a
particular use case is better expressed through a sequence diagram.