Co-Slicing for Program Comprehension and Reuse

When trying to understand certain behaviors of a given program, a programmer’s job can be facilitated by the use of a slicing tool, which helps focusing attention on the relevant subprogram. After, or even instead of reading a selected program slice, a programmer might be interested in studying its complement, i.e. the rest of the program. But what is that complement? Simply taking all statements outside the slice will not do, as some of the slice’s statements might be relevant too. Instead, one might ask which statements of a given slice can be removed from the original program, assuming the sliced results are already available. The removal of such redundant statements would yield a slice’s complement. This paper introduces the concept of a complement-slice, or simply co-slice, and demonstrates its use in both program comprehension and reuse. Moreover, the paper presents a provably correct co-slicing algorithm for a simple programming language, and outlines a corresponding solution for the general case.