Use Case Diagrams

A use case diagram depicts use case names, actors, relationships between actors and use cases, and relationships between use cases.

A relationship between an actor and a use case captures the fact that the actor participates in the use case.

Relationships between use cases include the include and extend relationships^4.1.

• The include relationship denotes the inclusion of a use case as a sub-process of another use case (the base use case).
• The extend relationship, denotes an extension of a use case as addition of 'chunks' of behaviors defined in an extension use case. These chunks of behaviors are added at specific places in a base use case called extension points.

  An extend relationship also includes a condition under which the extension can take place.

Figure 4.1: Example of Use Case diagram for a PM System.

The actors are 'Patient' and 'USER'. 'Doctor' and 'Nurse' are specializations of USER. The diagram includes use cases: 'Log in', 'Admit Patient', 'Silence alarm', 'Discharge Patient', 'Log out' and 'Log in secure'. 'Log out' is included by use cases: 'Admit Patient', 'Silence alarm' and 'Discharge Patient'. 'Log in secure' is an extension use case that extends use case 'Log in' under condition System security is high.

A use case model doesn't provide use cases details. UCEd includes an editor for that purpose. The next section describes use case description elements.