Reusing software developments

• Authors: Allen Goldberg
• Venue: SDE 4 Proceedings of the fourth ACM SIGSOFT symposium on Software development environments
• Year: 1990

Software development environments of the future will be characterized by extensive reuse of previous work. This paper addresses the issue of reusability in the context in which design is achieved by the transformational development of formal specifications into efficient implementations. It explores how an implementation of a modified specification can be realized by replaying the transformational derivation of the original and modifying it as required by changes made to the specification. Our approach is to structure derivations using the notion of tactics, and record derivation histories as an execution trace of the application of tactics. One key idea is that tactics are compositional: higher level tactics are constructed from more rudimentary using defined control primitives. This is similar to the approach used in LCF[12] and NuPRL[1, 8].Given such a derivation history and a modified specification, the correspondence problem [21, 20] addresses how during replay a correspondence between program parts of the original and modified program is established.Our approach uses a combination of name association, structural properties, and associating components to one another by intensional descriptions of objects defined in the transformations themselves.An implementation of a rudimentary replay mechanism for our interactive development system is described. For example with the system we can first derive a program from a specification that computes some basic statistics such as mean, variance, frequency data, etc. The derivation is about 15 steps; it involves deriving an efficient means of computing frequency data, combining loops and selecting data structures. We can then modify the specification by adding the ability to compute the maximum or mode and replay the steps of the previous derivation.