Software Evolution by Correctness Enhancement

Relative correctness is the property of a program to be more-correct than another with respect to a specification; this property enables us to rank candidate programs in a partial ordering structure whose maximal elements are the correct programs. Whereas traditionally we think of program derivation as a process of successive correctnesspreserving transformations (using refinement) starting from the specification, we argue that it is possible to derive programs by successive correctness-enhancing transformations (using relative correctness) starting from abort. One of the attributes of our approach is that it captures in the same mathematical model, not only the derivation of programs from scratch, but also most (if not all) of the activities that arise in software evolution. Given that most software is developed nowadays by evolving existing products rather than from scratch, any advance in the technology of program transformation by correctness enhancement stands to yield significant practical benefits.