A program slicing method for a wide spectrum language

Abstract

This thesis describes the implementation of a program slicer for WSL - a Wide Spectrum Language - which is a language that allows different levels of abstraction to coexist in the same program. WSL contains constructs not found in conventional languages, e.g. action systems (which model a segment of code with GOTOs and labels) and non deterministic constructs. Program slicing is a method for restricting a program to a specified behaviour of interest. Usually this behaviour of interest is expressed in terms of a variable or a set of variables. The method used in the thesis to slice a program is different from the classical ones in that slices do not need to be computed from an output statement, and in that slices are computed on a wide spectrum language closer to a functional language, instead of being computed on a more conventional, procedural language. A slicer for a subset of WSL has been designed and implemented based on the data flow analysis techniques for while-programs of Bergeretti and Carré [10]. It has been necessary to modify the algorithm to permit incremental slicing. Modifications of their algorithm were also needed to accommodate the specific WSL constructs mentioned above. The implementation has been developed using a rapid prototyping approach. The prototype has provided new ideas and enhancements for a more comprehensive sheer which could be implemented in the future. The slicer has assisted the maintainer using ReForm - a reverse engineering project developed at Durham University - in understanding and debugging a program by decomposing it. At the end of this thesis results showing how slicing has helped the maintainer are presented. Conclusions on the method used, the validity of the tool, and its engineering are also summarized.