Refining code-design mapping with flow analysis

Abstract

We address the problem of refining and completing a partially specified high-level design model and a partially-defined mapping from source code to design model. This is related but not identical to tasks that have been automated with a variety of reverse engineering tools to support software modification tasks. We posited that set-based flow analysis algorithms would provide a convenient and powerful basis for refining an initial rough model and partial mapping, and in particular that the ability to compute fixed points of set equations would be useful in propagating constraints on the relations among the model, the mapping, and facts extracted from the implementation. Here we report our experience applying this approach to a modest but realistic example problem. We were successful in expressing a variety of useful transformations very succinctly as flow equations, and the propagation of recursively-defined constraints was indeed useful in refining the mapping from implementation to model. On the other hand, our experience highlights remaining challenges to make this an attractive approach for general use. Special measures are required to identify and remove inconsistent constraints before they propagate through a system. Also, while the required flow equations are succinct, they are also rather opaque; it is not obvious how their expressive power might be preserved in a more accessible notation.