A Graph Representation for Use Case Specifications

Use cases represent widespread industrial approach to formulation and refinement of requirements specification on a system. Although in the last decade several formal representations of use cases were defined there is still gap between their practical use and those theories. This paper provides a formulation of semantics for use cases that is based on the theory of hierarchical graphs arguing that the definition despite its simplicity is powerful enough to represent all common aspects related with use case concepts. Use case specification is divided into three levels. At the bottom level each use case is considered as a flat graph of events. The middle level shapes use cases into episodes enabling to identify and reuse common fragments. The top level depicts interaction between actors and the modeled system through use case entities. Involving hierarchical graphs enables specifying all three levels in the consistent way and provides necessary abstraction on higher levels while all details is maintained in the bottom level.