A Note on Similarity of Specifications and Reusability of Transformational Developments

This paper explores the possibilities of reuse of transformational developments. Although it has often been claimed that this could be done fully mechanically, the experience with a number of derivations in this chapter indicates that this claim is somewhat preposterous. Only by describing the transformation steps in a very abstract way (using just natural language) and by considering very general specifications, can the developments be reused. The central concept is similarity, and several definitions of this informal notion are given, each leading to a particular kind of reuse of derivations. Variants of a derivation of linear search lead to several interesting search algorithms, culminating in derivations by reuse of two complicated string matching algorithms.