Relationships in use case:
There are five types of relationships:
- Association between Actor and Use case: An actor must be associated with at least one use case.
- Generalization of an Actor: One actor can inherit the role of another actor. The descendant inherits all the use cases of the ancestor.
- Generalization of a Use case: This is used when there are common behavior between two use cases and also specialized behavior specific to each use case.
- Include between two Use cases: The base use case is incomplete without the included use case. The included use case is mandatory and not optional.
- Extend between two Use cases: The extending use case is usually optional. It should be independent.