Using Program Slicing in Software Maintenance

Program slicing, introduced by Weiser, is known to help programmers in understanding foreign code and in debugging. We apply program slicing to the 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, we demonstrate how to form a slice-based decomposition for programs. We are then able to delineate the eeects of a proposed change by isolating those eeects in a single component of the decomposition. This gives maintainers a straightforward technique for determining those statements and variables that may be modiied in a component and those that may not. Using the decomposition, we provide a set of principles to prohibit changes that will interfere with unmodiied components. These semantically consistent changes can then be merged back into the original program in linear time. Moreover, the maintainer can test the changes in the component with the assurance that there are no linkages into other components. Thus, decomposition slicing induces a new software maintenance process model that eliminates the need for regression testing.