Analyzing projects using sequences

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:

  1. Add the VCR and accessories.
  2. Insert batteries in the remote control.
  3. Connect the antenna or cable system to the VCR.
  4. Set the CH3/CH4 switch.
  5. Turn on the VCR and select an active channel.
  6. Learn to use the TV/VCR button.
  7. Test the VCR connections.

Results

The specific sequence of steps through a particular use case is better expressed through a sequence diagram.


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