Relationships in use case.

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.