Functional Specifications for Old (and New) Software

Engineering is the use of science and technology to build useful artifacts. Those who design computer systems are clearly acting as engineers. However, there are deep differences between the way that computer systems are designed and the way that engineers in other areas work. Mechanical, electrical, and civil engineers make extensive use of mathematics to provide precise descriptions of their products. In contrast, computer systems are usually described, quite inaccurately, using anthropomorphic analogies and intuitive language. If an engineer produces a system from smaller components, he realises the necessity of precise specification of each of the components. Computer systems engineers, particularly programmers rarely write such specifications. They usually rely on a “cut and try” approach in which substantial redesign must be done after “integration” is begun.