Program refinement by transformation

Abstract

Program maintenance is simplified when the program to be modified can be viewed as an abstract algorithm to which clearly documented implementation decisions have been applied to produce an efficient realization. The Harvard Program Development System (PDS) [8] is a programming support environment that encourages users to take this view of programs. A user of the PDS creates transformations that incorporate implementation choices, and the system uses these transformations to refine concrete programs from their abstract counterparts. In addition to simplifying maintenance, this method supports the use of notational extensions and the development of program families. We describe the transformation facilities available to the user of the PDS, and we discuss aspects of the implementation of these facilities.