Developing the Use Cases

The use cases from the package diagram in JAD Session lesson from DAY 5, give a good picture of what the system will have to do. The team will have to flesh out each one. They've moved gradually from understanding the domain to understanding the system. The use cases have provided the bridge.

At no point in the JAD session did the development team discuss how the system would accomplish all the activities specified in the panolopy of use cases. The idea was just enumerate all the possible use cases. As the use cases become fleshed out in this hour, notice how the components of the Digital Library system start to materialize. At this point in the development effort, the system begins to take center stage.

note.GIF (411 bytes)To analyze the use cases, we have to run another JAD session. The discussion in this JAD session is intended to derive analysis for each use case.

The use case JAD session is usually the most difficult one, as it calls for the participants - potential users of the finished system - to become analysts. In their own niche, each one is a domain expert, and you have to tap into their expertise. Typically, they're not used to either verbalizing or analyzing what they know. It's also probably true that they haven't been part of a system design effort before, and they may be uncomfortable with trying to specify what a system should do to help them do their work.

The system-related steps in the scenario are extremely important. They'll show how the system is supposed to work. When the JAD session participants tell us these steps, they're telling us, in efect, what the system will ultimately look like. After this JAD session, we should have a good idea about the components of the system.

In Introducing a Use Case Model lesson in DAY 2, we see that each use case is a sequence of scenarios, and each scenarion is a sequence of steps. For each scenario in each use case, we'll want to show:

A brief description of the scenario
Assumptions for the scenario
The actor who initiates the use case
Preconditions for the use case
System-related steps in the scenario
Postconditions when the scenario is complete
The actor who benefits from the use case

Use cases that we're going to examine are numerous. That's why when we're performing an use case analysis number of them will be examined in detail, and the rest of them will be given to you as an exercise. Now let's dive into process of analysis the use case.