Formal modelling of use cases with X-machines

Use cases are a popular method for capturing the behavioral requirements of software systems. They are usually written in informal text form describing the interactions between users and the system. Use cases are the central driving artifacts in Unified Process (UP), an agile software methodology. Testing plays a very important role in UP and other agile methodologies, such as Extreme Programming. X-machines is a formal method for the specification of systems. Furthermore, a method for testing systems specified by X-machines exists that generates a complete test case set. This paper proposes the integration of X-machines in the UML use case model, in order to facilitate the generation of a complete test case set for system testing. We present a transformation that semi-automatically transforms use case text into its corresponding X-machine model and we demonstrate the transformation by using the example of an ATM. We also suggest some improvements in the design of X-machine models, such as the use of compound inputs (consisting of interaction functions and data) and a structured representation of the memory, giving an object-oriented flavor, and we discuss the benefits of these improvements.

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