Some optimal object-based architectural features for corrective maintenance

We investigate the relationship between some characteristics of software architecture present at the top-level design stage and the resulting corrective maintainability of five Ada systems. Measures are developed for both internal and external complexity for the subset of packages, within our five projects, that were changed to correct a software fault. These measures involve the context coupling of packages and the number of visible declarations that can be exported by a package. A relationship establishing the optimal number of object couples as a function of the mean number of visible declarations is empirically estimated based on the faults contained within our projects. We find that the optimal number of object couples varies inversely with the mean number of visible declarations. When initially designing a system, or when making modifications to an existing system, this relationship can be used to provide guidance for choosing the most maintainable design among alternative designs.