Is there such a thing as a use case relationship diagram?

Question

I know about use case diagrams. But is there something called a use case relationship diagram? How is it different?

Answer 1

You must be thinking of Use Case relationships. Quoting wikipedia:

Use Case Relationships

Three relationships among use cases are used often in practice.

Include

In one form of interaction, a given use case may include another. "Include is a Directed Relationship between two use cases, implying that the behavior of the included use case is inserted into the behavior of the including use case"[1].

The first use case often depends on the outcome of the included use case. This is useful for extracting truly common behaviors from multiple use cases into a single description. The notation is a dashed arrow from the including to the included use case, with the label "«include»". This usage resembles a macro expansion where the included use case behavior is placed inline in the base use case behavior. There are no parameters or return values. To specify the location in a flow of events in which the base use case includes the behavior of another, you simply write include followed by the name of use case you want to include, as in the following flow for track order.

Extend

In another form of interaction, a given use case (the extension) may extend another. This relationship indicates that the behavior of the extension use case may be inserted in the extended use case under some conditions[1]. The notation is a dashed arrow from the extension to the extended use case, with the label "«extend»". Notes or constraints may be associated with this relationship to illustrate the conditions under which this behaviour will be executed.

Modelers use the «extend» relationship to indicate use cases that are "optional" to the base use case. Depending on the modeler's approach "optional" may mean "potentially not executed with the base use case" or it may mean "not required to achieve the base use case goal."

Answer 2

A use case diagram contains one use case. In RUP, there's a use case domain model that displays the relationship between the different use cases. In a use case, you can also include and extend other use cases, which also displays a certain relationship between use cases.

RUP stands for Rational Unified Process, it's a widely used development process, especially in a bit more formal organisations. It makes heavy use of UML diagrams. http://nl.wikipedia.org/wiki/Rational%5FUnified%5FProcess

Answer 3

Here's more information about showing relationships between use cases: UML Use Case Diagrams: Reference at http://msdn.microsoft.com/en-us/library/dd409427%28VS.100%29.aspx

Include: An including use case calls or invokes the included one. Inclusion is used to show how a use case breaks into smaller steps. The included use case is at the arrowhead end.

Extend: An extending use case adds goals and steps to the extended use case. The extensions operate only under certain conditions. The extended use case is at the arrowhead end.