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Lesson 3The use case diagram
ObjectiveIdentify the four fundamental modeling elements of a use case diagram.

Use Case Diagram

The use case model has three components. The first component, and the only one actually defined by the UML, is the use case diagram. To supplement the diagram, it is almost always necessary to add a use case narrative. Once a use case is fully described, it is possible to dissect it into scenarios, or test cases.
Remember that although diagrams are extremely valuable and provide substantial information, they nearly always require some form of explanation to put them into context and ensure their proper interpretation.

Use case diagram

Four modeling elements make up the use case diagram: system, actors, use cases, and associations.

  1. Actor: People, systems, and devices that have a stake in the successful operation of the system
  2. System: Sets the context of the system in relation to the actors who use it and the features it must provide.
  3. Use case: Identifies the key features of the system. Without these features, the system will not fulfill the user/actor requirements. Each use case expresses a goal that the system must achieve
  4. Association: Identifies an interaction between elements

Use Case Diagram Elements
Each association becomes a dialog that must be explained in a use case narrative. Each narrative in turn provides a set of scenarios that function as test cases when evaluating the design and implementation of the use case.
In the next lesson, you will learn about the use case system element.

Use Case Diagram