Checking consistency in UML diagrams: Classes and state machines

One of the main advantages of the UML is its possibility to model different views on a system using a range of diagram types. The various diagrams can be used to specify different aspects, and their combination makes up the complete system description. This does, however, always pose the question of consistency: it may very well be the case that the designer has specified contradictory requirements which can never be fulfilled together. In this paper, we study consistency problems arising between static and dynamic diagrams, in particular between a class and its associated state machine. By means of a simple case study we discuss several definitions of consistency which are based on a common formal semantics for both classes and state machines. We furthermore show how consistency checks can be automatically carried out by a model checker. Finally, we examine which of the consistency definitions are preserved under refinement.