What is a Use Case Realization? - UML

The last chapter on basic OO design principles looked at little fragments of design problems. In contrast, this chapter demonstrates the larger picture of designing the domain objects1 for an entire use case scenario. You will see larger - scale collaborations and more complex UML diagrams.

To quote, "A use - case realization describes how a particular use case is realized within the Design Model, in terms of collaborating objects" [RUP]. More precisely, a designer can describe the design of one or more scenarios of a use case; each of these is called a use case realization (though non - standard, perhaps better called a scenario realization). Use case realization is a UP term used to remind us of the connection between the requirements expressed as use cases and the object design that satisfies the requirements.

UML diagrams are a common language to illustrate use case realizations. And as we explored in the prior chapter, we can apply principles and patterns of object design, such as Information Expert and Low Coupling, during this use case realization design work.

To review, Figure illustrates the relationship between some UP artifacts, emphasizing the Use Case Model and the Design Model - use case realizations.

Artifact relationships, emphasizing use case realization

Artifact relationships, emphasizing use case realization

Some relevant artifact - influence points include the following:

  1. The use case suggests the system operations that are shown in SSDs.
  2. The system operations become the starting messages entering the Controllers for domain layer interaction diagrams. See Figure.
    • This is a key point often missed by those new to OOA/D modeling.
  3. Domain layer interaction diagrams illustrate how objects interact to fulfill the required tasks - the use case realization.

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