Stepwise refinement revisited

In this paper, rigorous application of stepwise refinement is explored. The steps of definition, decomposition, and completion are described, where completion is a newly introduced step. This combination of steps extends the use of stepwise refinement to larger systems. The notions of range, active objects, and backlog interface are introduced. Verification of incomplete programs via interactive testing is described. The paradigm is demonstrated in an example. The relationship between the paradigm and the current programming languages is considered. It is argued that the WHILE-DO loop is a harmful construct from this point of view.