We don't use any known formal method, excepting that ours is essentially an object oriented approach to design. When I got down to really understanding OOPL systems, I was struck by just how much we had already done instinctively. It is perfectly possible to write in an OOPL style I think, but without polymorphism, which is a whole bag of worms anyway, and almost certain to mean unusable bloat in embedded applications.

Steve