Professional engineers can often be distinguished from other designers by the engineers ability to use mathematical models to describe and 1 analyze their products. This observation by Parnas describes the de facto professional standards in all classical engineering disciplines (civil, mechanical, electrical, etc.). Unf- tunately, it is in sharp contrast with current (industrial) practice in software design, where mathematical models are hardly used at all, even by those who, 2 in Holloway s words aspire to be engineers. The rare exceptions are certain critical applications, where...