REAL-TIME LOGIC, GRAPH-THEORETIC ANALYSIS, AND MODECHART A real-time system can be specified in one of two ways. The first is to structurally and functionally describe the system by specifying its mechanical, electrical, and electronic components. This type of specification shows how the components of the system work as well as their functions and operations. The second is to describe the behavior of the system in response to actions and events. Here, the specification tells sequences of events allowed by the system | Real-Time Systems Scheduling Analysis and Verification. Albert M. K. Cheng Copyright 2002 John Wiley Sons Inc. ISBN 0-471-18406-3 CHAPTER 6 REAL-TIME LOGIC GRAPH-THEORETIC ANALYSIS AND MODECHART A real-time system can be specified in one of two ways. The first is to structurally and functionally describe the system by specifying its mechanical electrical and electronic components. This type of specification shows how the components of the system work as well as their functions and operations. The second is to describe the behavior of the system in response to actions and events. Here the specification tells sequences of events allowed by the system. For instance a structural-functional specification of the real-time anti-lock braking system in an automobile describes the braking system components and sensors how they are interconnected and how the actions of each component affects the other. This specification shows for example how to connect the wheel sensors to the central decision-making computer that controls the brake mechanism. On the other hand a behavioral specification shows only the response of each braking system component in response to an internal or external event but does not describe how one can build such a system. For instance this specification shows that when the wheel sensors detect wet road conditions the decision-making computer will instruct the brake mechanism to pump the brakes at a higher frequency within 100 ms. Since we are interested in the timing properties of the system a behavioral specification without the complexity of the structural specification often suffices for verifying the satisfaction of many timing constraints. Furthermore to reduce specification and analysis complexity we restrict the specification language to handle only timing relations. This is a departure from techniques that employ specification languages capable of describing logical as well as timing relations such as real-time CTL. 148 EVENT-ACTION MODEL 149
