Evaluation of Underdetermined Explicit Definitions

. The specification language VDM-SL is used in the modeloriented formal method known as the Vienna Development Method. There have been a number of different dialects of this language, but a standard for the language has now been defined. The draft standard includes a dynamic semantics which, in general, is not executable. A given specification denotes a (possibly infinite) set of models according to the dynamic semantics. This paper illustrates how all the valid results from evaluating a given expression in all the different models can be collected. It is important to be able to do this in order to investigate the amount of looseness which is present in the given specification, such that correctness properties of the expression as a whole can be derived. We present a specification of such a loose evaluation for an executable subset of VDM-SL. The subset is interesting because it also illustrates how underdeterminedness is combined with recursion in VDM-SL. 1 Introduction Formal specif..