Augmenting Sequence Enumeration with String-Rewriting for Requirements Analysis and Behavioral Specification

Sequence enumeration is a method for deriving a system model based on informal requirements. Under sequence enumeration, stimulus (input) sequences are considered in a breadth-first manner, with the expected system response to each sequence given. Not all sequences of stimuli are considered since a sequence need not be extended if either it is illegal (it cannot be applied in practice) or it can be reduced to another sequence previously considered (the sequences take the system to the same state). Sequence enumeration is mostly a manual process, which leads to a model that can be used as the basis for automation. This paper describes a method, based on string-rewriting, that automates parts of sequence enumeration. This automation has the potential to reduce both the cost and time involved in sequence enumeration but also to reduce the scope for human error. In addition to outlining this method, we discuss our experiences in applying it to four case studies.