Applying Techniques to Skeletons

This paper concerns our research on developing a theory and methodology appropriate for systematically building complicated Prolog programs. Programs are constructed procedurally from standard components. We identify skeletons, basic Prolog programs with a well-understood control ow, and techniques, standard Prolog programming practices, as basic components. Applying a technique to a skeleton creates an extension of the skeleton. Complicated programs are built by choosing a skeleton and repeatedly applying techniques. Separate extensions of the same skeleton can be composed into a single program, simplifying the process of program development. We describe our application of skeletons and techniques within the framework of Shapiro's Model Inference System. 1.1 INTRODUCTION Stepwise reenement, as advocated by Wirth Wir71], emerged as a methodology to develop programs in procedural programming languages to produce clear, well structured code. There is no analogous method for the systematic construction of Prolog programs. Sporadic attempts have been made over the years to automati-cally/systematically construct logic programs, for example LP90, Fri90]. However, much of the eeort has been concentrated on logic and formal transformations. Our experience in teaching Prolog suggests that students do not naturally develop programs by developing and then transforming correct statements of logic. Rather, they think of programming in procedural terms. This need not connict with the declarative ideal of logic programming if well structured programs are used. Procedural be