Program slicing is applied to the software maintenance problem by extending the notion of a program slice (that originally required both a variable and line number) to a decomposition slice, one that captures all computation on a given variable, i.e., is independent of line numbers. Using the lattice of single variable decomposition slices ordered by set inclusion, it is shown how a slice-based decomposition for programs can be formed. One can then delineate the effects of a proposed change by isolating those effects in a single component of the decomposition. This gives maintainers a straightforward technique for determining those statements and variables which may be modified in a component and those which may not. Using the decomposition, a set of principles to prohibit changes which will interfere with unmodified components is provided. These semantically consistent changes can then be merged back into the original program in linear time.>

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.>

A local area network of workstations often has a number of idle workstations that could be used to lower the load of active workstations. Widely used operating systems, such as Unix, often have the capability of remotely executing a program, but no automatic load balancing facilities. The authors report on a low-cost solution to workstation load redistribution by allowing the shell to select an alternate host for command execution.>