Identification of program modifications and its applications in software maintenance

It is pointed out that a major problem in software maintenance is the revalidation of a modified code. It is economically desirable to restrict that process only to those parts of the program that are affected by the modifications. Towards that goal, a formal method is needed to identify the modifications in an automatic way. Such a method is proposed in the present work. The modifications are localized within clusters in the flow graphs of the original and modified programs. Both flow graphs are transformed into reduced flow graphs, between which an isomorphic correspondence is established. Cluster-nodes in the reduced graphs encapsulate modifications to the original program. An algorithm to derive the reduced flow graphs has been implemented as an extension to the recently developed system for testing and debugging (STAD 1.0) and early experiments with the algorithm are reported. Potential applications in regression testing and reasoning about the program are discussed