In UML, relationships are connections between model elements. Use cases are also connected to each other in different kinds of relationships. The relationship between two use cases basically models the dependencies between two use cases. By reusing existing use cases using different types of relationships, the overall effort required to develop the system is reduced.
Use case diagrams show use cases, actors, and the relationships between them. For example, the relationship between an actor and a use case illustrates that the actor can use certain functionality of the business system.
An association is a relationship between two classifiers, such as an actor and use cases, that describes the cause of the relationship and the rules that govern it. An association is a relationship between an actor and a business use case. It indicates that an actor can use the functionality of the business system.
A generalization relation is a relationship in which one model element (child) is based on another model element (parent). Generalization relations are used in class diagrams, component diagrams, deployment diagrams, and use case diagrams to indicate that the child element accepts all the attributes, operations, and relationships defined in the parent element.
In UML modeling, a Include relationship is a relationship in which one use case (base use case) contains the functionality of another use case (inclusion use case). A containment relationship supports the reuse of functionality in the use case model.
In UML modeling, you can use an extend relationship to specify that one use case (extension) extends the behavior of another use case (base). This type of relationship reveals details about the system or application that are usually hidden in the use case.
More Use Case Examples
Broadcasting System Use Case Diagram
ATM Use Case Diagram Example
Use Case Diagram: Multiple Projects with System Boundaries
Use Case Diagram: Online Examination System
Use Case Diagram Example: Passenger Service
Use Case Diagram Example: Software Development
Use Case Diagram Example: Carpark System
UML Use Case Diagram: Order Process System
Include and Extend Use Case Diagram
Use Case Diagram Example: Website (Extend and Include Use Case)
Use Case Diagram Example: External System as Actor
Use Case Diagram Example: Bank ATM
Use Case Diagram Example: Airport