In this talk, 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. I will report our experience applying this approach to a modest but realistic example problem.