CS2002 - Lecture 2 - Use Case Diagrams

What is being described in a use case diagram?

The system

Who interacts with the system?

The actors

What can the actors do?

The use cases

What do use cases do?

A use case describes a specific functionality expected from the system under development

What are actors?

Actors represent roles that interact with the system, either by initiating use cases or providing data for use cases

What is a primary actor?

An actor who benefits directly from the execution of a use case

What is a secondary actor?

An actor who does not benefit directly but provide services to the system

What do active actors do?

Initiate the execution of a use case

What do passive actors do?

Support the execution by providing necessary information or services

How are use cases and actors connected in a use case diagram?

Use cases and actors are connected via solid lines (associations) to indicate communication

What is a Include Relationship?

When the behaviour of one use case (the included use case) is incorporated into another use case (the base use case)

Can the base use case function without the included use case in an Include relationship?

No, the base use case cannot function without the included use case, implying a mandatory relationship

What is an Extend relationship?

When an extending use case adds optional behavior to a base use case

Can the base use case function without the extended use case in an Extend relationship?

Yes, the base use case does not depend on the extending use case for its execution, making the relationship optional

What is a Generalisation relationship?

A generalisation relationship exists when one use case (the base use case) is specialized by another (the sub use case)

What does the sub use case in a generalisation relationship do?

The sub use case inherits the behavior and relationships of the base use case, but it can modify or extend the behavior

What does generalisation allow for actors?

Generalization allows actors to inherit communication capabilities from other actors

What are the elements of a use case?

Name, Short description, Precondition, Postcondition, Error situations, System state on the occurrence of an error, Actors, Trigger, Standard process, Alternative processes