On the semantics of the extend relationship in use case models: Open-closed principle or clairvoyance?

Abstract

A use case is a description of the interactions of a system with the actors that use it. The Achilles' heel of use cases is the unclear UML semantics, in particular the definition of the extend relationship. This article is an attempt to clarify the semantics of the extension mechanism. In particular, we advocate for the application of the open-closed principle, adding modification details in the extending use case, instead of in the base case. A revision of the UML standard would be impractical, but a disciplined reinterpretation of the extend and extension point concepts could represent a great improvement. Textual and graphical approaches (based in the UML Behavior meta-model) are considered. Using these recommendations, the base use cases can be independently described, while the extending use cases will be self-contained. © Springer-Verlag Berlin Heidelberg 2010.