CASE Design Maintenance

proven difficult in the absence of design information [19]; maintainers often spend considerable energy trying to recover this design information before making changes [15]. Capture and reuse of certain kinds of design informa-tion should consequently improve the maintenance process. Updating the design information is as important as revising the software itself, for the revised design information is necessary for further maintenance. Four major software engineering efforts that ended in disaster precisely because trying to main-tain their designs was perceived as impractical are described by [23]. Conse-quently, each design was abandoned and the projects spiraled into chaos. Rather than emphasize software maintenance, we suggest that design maintenance become the key focus, with programs being easily derived from a complete design. The details of our work lay foundations for such design maintenance systems (DMS). This article sketches such a system. In particular, it defines the kinds of information such a system must retain and a particular ap-proach to capture and modify that information. For more details, the reader is referred to [6]. We believe that productivity ad-vances in software construction and maintenance depend on automa-tion, which, in turn, depends on formalization. Our approach fo-cuses on theories and mechanisms necessary to allow formal mainte-nance deltas to be integrated into software systems constructed by rigorous, if not completely auto-matic, means. Such deltas express desired changes in program func-tionality, performance, and imple-mentation technology. Figure 1 shows a life cycle model establishing the context for a DMS. Most of the mechanisms are concerned with comparing the existing artifact with some ideal, and producing a main-tenance delta describing the error. If one had a design maintenance system based on integrating formal deltas, then the life cycle notions of design/coding phases and mainte-nance phases become indistinguish-able. Software would be con-structed by incrementally revising a current design according to a con-tinuous stream of maintenance del-tas generated by comparing ex-pected consequences of the current design with customer desires and available implementation technolo-gies