Use Case Diagram
How do we visualize a system’s use cases?
Purpose
A use case diagram shows the relationship among actors and use cases within a system.
Definition
A use case diagram is a graph with
- Actors
- Use cases
- System Boundary
- Communication (participation) relationships between actors and use cases
- Generalizations among the use cases
Examples
Terminology
Use Case
A coherent unit of functionality provided by a system or class as manifested by sequences of messages exchanged among the system and one or more external interactors together with actions performed by the system.
Actor
Role of an object or objects outside the system that interacts directly with the system. (A Use Case Diagram shows actors as classes, not objects; in fact an actor is just a class with the stereotype «actor».)
Relationships
| Communicates | Extends | Uses |
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| A participates in U | U is a kind of variation on V (V might be the "normal" behavior and U is done in unusual or exceptional circumstances). | An instance of U will include all of the behavior specified by V. |
