Aims

An important aspect of the analysis of a model is gaining confidence that the model is an accurate reflection of the informally stated requirements. This chapter aims to provide an awareness of the techniques through which such confidence can be gained. The idea of model validation is introduced: checks for internal consistency are discussed; techniques of visualisation, integration with legacy code, testing and proof are illustrated. On completion of this chapter, the reader should be equipped to choose appropriate validation techniques for a given modelling task.

Introduction

In previous chapters we have introduced a number of different models in VDM-SL. In several cases (e.g. the alarm example in Chapter 2) we started from an informal collection of requirements and built up a model in stages. But just how confident can one be that the formal model really describes the system the customer wanted? This problem arises continually in industry. When the imprecision of the customer requirement is replaced by the precision of a model, how can the modeller be sure that those areas of incompleteness and ambiguity in the original requirement have been resolved in a way that satisfies the customer? There is a further complication: requirement documents often state the client's intentions incorrectly. Such errors can only be resolved by somehow presenting a model of the system to the client in order to obtain feedback which may lead to modifying the model.