UML Weekend Crash Course™ - To Parent Directory

52
Saturday Morning
Use Case scenarios
A Use Case scenario is one logical path through a Use Case, one possible sequence of steps
in the execution of the Use Case. A Use Case may include any number of scenarios. The set
of scenarios for one Use Case identifies everything that can happen when that Use Case is
used. Consequently, the set of scenarios becomes the basis for your test plan for the Use
Case. As the application design deepens, the test plans are expanded to keep the tests
focused on the original expectations for the Use Case expressed in the scenarios.
These three elements — the Use Case diagram, narrative, and scenarios — comprise the
Use Case Model. The remainder of this session is devoted to the Use Case diagram. Session 7
covers the Use Case narrative, and Session 8 covers the Use Case scenarios.
Defining the Elements of the Use Case Diagram
Of the three elements that comprise the Use Case Model, the only one actually defined by
the UML is the Use Case diagram (Figure 5-3).
2. System
3. Use Case
5. Dependency
1. Actor
4. Association
6. Generalization
Figure 5-3 Elements of a Use Case diagram
Six modeling elements make up the Use Case diagram: systems, actors, Use Cases, associations,
dependencies, and generalizations.
System: Sets the boundary of the system in relation to the actors who use it (outside
the system) and the features it must provide (inside the system).
Actor: A role played by a person, system, or device that has a stake in the successful
operation of the system.
Use Case: Identifies a key feature 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.
Association: Identifies an interaction between actors and Use Cases. 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
analysis, design, and implementation of the Use Case.