The architectural specification of an avionic subsystem

The work of the British Aerospace Dependable Computing Systems Centre includes the development of formal techniques for use in defining and tracing requirements for software systems at the system architecture level. A basic repertoire of techniques proposed so far includes the graphical representation of timing requirements allied to model-oriented specifications of functionality. This paper gives an overview of these techniques and reports on a small study in their application conducted by British Aerospace Defence. The study uses a realistic example of an avionics system: the pilot data entry system for a waypoint database. The example is described with some technical detail. Formally analysing a timing requirement for the rate of data entry yields local timing requirements for the cockpit equipments. Conclusions assess the value of these techniques, as perceived by BAe systems developers, and propose further work in providing tool support.