Introduction

Abstract

All around us in everyday life are complex systems of men and machines. Automobile plants, steel foundries, telephone exchanges, ticket reservation systems, banking systems, air flight control systems, local transport systems, etc. spring to mind. For these to function properly, we need to be able to understand them and how they react to emergencies (perhaps a bus breaks down in the rush hour), continual high pressures (rush hour traffic) as well as under normal circumstances (traffic in off-peak periods). Since the world is continually changing, systems have to adapt to new circumstances, e.g. how does the building of a new town nearby affect the local bus company? Which extra services should be provided and thus how many extra buses and crew will be needed? We may also need to implement totally fresh systems — how then do we justify and test our designs?