Use Cases as views: A formal approach to Requirements engineering in the Unified Process

In Requirements Engineering structural and functional requirements for a new software system are gathered, analyzed, and manifested. Unfortunately the connection between these aspects gets lost in the standard object oriented methodology and has to be re-established later on. Not only is this tedious work but the detection of conflicts and inconsistencies in early phases is hindered by the separation of static and dynamic aspects. We propose the use of graph transformations to specify the connection between these aspects. Based on what we call an integrated business model, consistency analysis at the requirements model level becomes possible. Keywords: UML, Unified Process, functional specifications, integrated business model, graph transformation 1 Introduction At the beginning of each software development there are several ideas or visions of what the system to be build should achieve. The techniques developed in the area of requirements engineering are concerned with gathering, structuring and integrating these different ideas for the new system. It is the goal of this process to achieve a set of reasonable and consistent requirements for the further development process. The main problem is the detection and resolution of inconsistencies and conflicts between competing requirements. The application of formal methods and notations promises to support this task by enabling automated analysis. Although multiple formal methods have been proposed by scientists (see e.g. [7] for a survey), the standard methodologies in object oriented software engineering still use very informal and imprecise techniques in this phase of the development process. In particular, what is missing is a coupling between the structural (data) description (captured in class diagrams) and the behavior of the system (captured in activity and use case diagrams). In this paper we will show how to improve this situation by giving use cases a precise description, thus achieving a coupling of the dynamic and static parts of the model. This allows to apply formal techniques of consistency analysis. The paper is organized as follows: Section 2 gives an introduction to the requirements analysis phase in the Unified Process (UP) and points out some weak points of this approach. We will advance the basic ideas presented in the UP by further elaborating the ideas of a business model and formalizing their notion in Section 3. Section 4 introduces use case diagrams and their new role in the context of the integrated business model. Section 5 extends the notion of views to structure the whole requirements model and the concluding Section 6 gives perspectives toward further work on this topic.