Use Case Diagram

A use case diagram ( engl. use case diagram ), also Nutzfalldiagramm, is one of 14 types of diagrams of the Unified Modeling Language (UML), a language for modeling the structure and behavior of software and other systems. It provides use cases and actors with their respective dependencies and relationships dar.

The use case diagram is a behavior chart. It shows a particular view of the expected behavior of a system and is therefore used for the specification of requirements for a system.

A use case diagram is not a flow description dar. This may instead be represented by an activity, a sequence or a collaboration diagram (from UML 2.x communication diagram ).

Use case diagram in bullet points

• The goal is as simple as possible to show what you want to do with the software system to be built, in which cases the application so there.
• Actors are called " stick figure " shows which both subjects such as customers or administrators, as well a system can represent (for systems a tape symbol is sometimes used ).
• Applications are shown in ellipses. You need to be described (eg, in a comment or a separate file ).
• Associations between actors and use cases must be marked by lines.
• System limits are indicated by rectangles.
• Include relationships are marked by ( marked with << include >> ) dashed line and an arrow to the included use case where this is necessary for the calling application.
• Extend relationships are marked by ( with << extend >> marked ) dashed line and arrow, from the extending use case, this can be activated by the calling application, but not necessarily.

Elements

Actors are called " stick figure " shows which both subjects such as customers or administrators, as well a system can display.

Applications are shown in ellipses. You need to be described (eg, in a comment or a separate file ).

Relations

Multiplicity of actor and use case, the default is 1 of the actor.

Generalization of use cases.

Generalization of actors.

Include relationship in the use case diagram, use case where A includes the use case B.

Extend relationship in use case diagram, use case where A extends the use case B.

Extend relationship with extension point, where application A extends the use case B under the specified condition.

Use case with extension point.

Examples

The figure at right shows a more complex use case diagram that captures the relationship between the actor and the system user multimedia system. A user is interested in four use cases, which in turn are interrelated. Create music CD is the most complex application, because it imports two other applications, and is optional, expanded by a third, label CD.

Differences to the UML 1.x

The use case diagram is re-classified as a behavior chart and no longer as a structural diagram in the UML2. In addition, players now have to have a name and the preconditions of the respective extension points must be appended by note to the appropriate extension relationship.