Examples of how to determine the specifications of control systems

Abstract. Creating the specification of a system by focusing primarily on the detailed properties of the digital controller can lead to complex descriptions that have no coherence. An argument put forward in a re-cent paper by Hayes, Jackson, and Jones gives reasons to focus first on the wider environment in which the system will reside. This paper infor-mally explores two examples so as to illustrate this approach to system specification. 1 Overview of approach The general idea of the “Hayes/Jackson/Jones ” approach [HJJ03] is simple: for many technical systems it is easier to derive their specification from one of a wider system in which physical phenomena are measurable. Even though the computer cannot affect the physical world directly, it is still worthwhile to start with the wider system. The message can be stated negatively: don’t jump into specifying the digital system in isolation. If one starts by recording the requirements of the wider (physical) system, the specification of the technical components ca