Scenario-driven modeling and validation of requirements models

Requirements models for large systems typically cannot be developed in a single step, but evolve in a sequence of iterations. We have developed such an iterative modeling process which is based on the interactive simulation of yet incomplete and semi-formal models. Missing parts are completed interactively by the user simulating the model. We start by modeling type scenarios (i.e. use cases) and simulate these interactively before having specified any system behavior. Such simulation runs yield exemplary system behavior in form of message sequence charts (MSCs). The modeler can then generalize this recorded partial behavior into statecharts. The resulting model is simulated again, (i) for validating that the modeled behavior matches the previously recorded behavior, and (ii) for recording new yet unspecified behavior in a next iteration step. Thus, recording MSCs by playing-through the scenarios and transforming MSCs to statecharts stimulate and drive each other.In this paper we focus on two elements of our approach: firstly, we describe the syntax and semantics of our scenario language. Secondly, we give an example how our modeling process works.