The Use Case Realization

In Chapter 5 when we talked about use cases, we pointed out clearly that the use cases only show what the system can provide to its users without explaining how. Therefore, the use case model helps one to understand what the users can ask the system to do, without showing how the system will do it.

Now, it is the time to consider how the system will provide its services to the users. This is achieved by developing for each use case its realization. The realization describes how the behavior of a use case will be provided by collaboration of different elements of the system. The realization of a use case can be presented using UML interaction diagrams or textually using structured English.

It is important to note that the separation of use cases from the use case realization decouples the process of gathering requirements (expressed in a synthetic way in the use case model) from the design of the model (explicitly expressed in the use case realization). This separation allows developers to focus on one well-defined problem at a time and avoid dealing with design issues during the phase of analysis and vice versa. Figure 8-3 shows the UML notation of the use case realization. The dotted eclipse represents the use case realization and the dotted arrow represents the realization association. For each use case of the model, a use case realization should be developed.

Start Simulation

Start Simulation Realization

Realization ^ realti onship

Figure 8-3. The use case realization for Start Simulation use case.

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