Use Case Diagrams

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

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

Relations between use cases include the include, extend relations^4.1.

• The include relation denotes the inclusion of a use case as a sub-process of another use case (the base use case). By default, the control resumes to the including use case only after the successful completion of the included use case (primary scenario). Control resumption from secondary scenarios can be explicitly specified using [continue statement.
• The extend relation 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 relation 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.