Using program decomposition to guide modifications

The authors use data-flow techniques to form a notion of direct sum decomposition for programs. The decomposition yields a method and guidelines for software maintainers to use so that changes can be assured to be completely contained in the modules under consideration and that there are no undetected linkages between the modified and unmodified code. Thus, the impact of small changes can be gauged. The decomposition can also be used to limit the amount of testing required to assure that the change is correct; under suitable conditions, modification testing will be required only for the changed code. Moreover, if these hypotheses are violated, the modifier can be virtually assured that proposed changes will have a wider impact than that which is contemplated