Using an object-oriented methodology to bring a hybrid system from initial concept to formal definition

Abstract

A real-time embedded system is characterised by the interaction between a discrete control program and an environment with continuous and discrete nature. Because a real-time embedded system interacts and controls a real world system, issues such as liveness and safety can be critically important. The failure of such a system to meet it liveness and safety constraints can result in large economic costs and the loss of life. The behaviour of such systems needs to verified. The first step to verifying the behaviour of a system is to formally specifying the system. Hybrid automata provide a formalism for specifying and modelling both the continuous and discrete nature of the entire system. In common with other formal methods, deriving a hybrid automata description of anything but a toy system is not a trivial task. Two factors that make the derivation a formal specification difficult are:

• bridging the “detail gap” between the initial descriptions of a system and its formal specification; and

• managing the scale of real world applications.

This paper presents a methodology that addresses these problems. This methodology OHMS (Object-oriented Methodology for Hybrid Systems) assists the user in capturing the initial system requirements, identifying the component parts of the system, defining the interfaces between these components, and incrementally developing these into a hybrid automata specification of the system. The major aspects of this methodology are illustrated with a simple case study.