Use Case Diagrams

A use case diagram is a UML diagram that provides a graphical view of the requirements of your system, and helps you identify how users interact with it.

With a use case diagram, you immediately see a snapshot of the system functionality. Further details can later be added to the diagram if you need to elucidate interesting points in the system behavior.

A use case diagram is well suited to the task of describing all of the things that can be done with a database system by all the people who might use it. However, it would be poorly suited to describing the TCP/IP network protocol because there are many exception cases, branching behaviors, and conditional functionality (what happens when the connection dies, what happens when a packet is lost?)

In the following example, the actor "photographer" does two things with the camera: take pictures and change the film. When he takes a picture, he has to switch the flash on, open the shutter, and then close the shutter but these activities are not of a high enough level to be represented in a use case.

• Use Case Diagram Objects
  PowerDesigner supports all the objects necessary to build use case diagrams.
• Use Cases (OOM)
  A use case is an interaction between a user and a system (or part of a system). It defines a discrete goal that a user wants to achieve with the system, without revealing the system's internal structure.
• Actors (OOM)
  An actor is an outside user or set of users that interact with a system. Actors can be humans or other external systems. For example, actors in a computer network system may include a system administrator, a database administrator and users. Actors are typically those entities whose behavior you cannot control or change, because they are not part of the system that you are describing.
• Use Case Associations (OOM)
  An association is a unidirectional relationship that describes a link between objects.