ERC: an Object-Oriented Refinement Calculus for Eiffel

We present a refinement calculus for transforming object-oriented (OO) specifications (or lsquocontractsrsquo) of classes into executable Eiffel programs. The calculus includes the usual collection of algorithmic refinement rules for assignments, if-statements, and loops. However, the calculus also deals with some of the specific challenges of OO, namely rules for introducing feature calls and reference types (involving aliasing). The refinement process is compositional in the sense that a class specification is refined to code based only on the specifications (not the implementations) of the classes that the specification depends upon. We discuss how automated support for such a process can be developed based on existing tools. This work is done in the context of a larger project involving methods for the seamless design of OO software in the graphical design notation BON (akin to UML). The goal is to maintain model and source code integrity, i.e., the software developer can work on either the model or the code, where (ideally) changes in one view are reflected instantaneously and automatically in all views.