Automatic Analysis of Hybrid Systems
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Hybrid systems are real-time systems that react to both discrete and continuous activities (such as analog signals, time, temperature, and speed). Typical examples of hybrid systems are embedded systems, timing-based communication protocols, and digital circuits at the transistor level. Due to the rapid development of microprocessor technology, hybrid systems directly control much of what we depend on in our daily lives. Consequently, the formal specification and verification of hybrid systems has become an active area of research.
This dissertation presents the first general framework for the formal specification and verification of hybrid systems, as well as the first hybrid-system analysis tool--H scYT scECH. The framework consists of a graphical finite-state-machine-like language for modeling hybrid systems, a temporal logic for modeling the requirements of the hybrid systems, and a computer procedure that verifies modeled hybrid systems against modeled requirements. The tool H scYT scECH is the implementation of the framework using C++ and M scATHEMATICA.
More specifically, our hybrid-system modeling language, Hybrid Automata, is an extension of timed automata (AD94) with discrete and general continuous variables whose dynamics are governed by differential equations. Our requirement modeling language, I scCTL, is a branching-time temporal logic, and is an extension of T scCTL (ACD93) with stop-watch variables. Our verification procedure is a symbolic model-checking procedure that verifies linear hybrid automata against I scCTL formulas, and is an extension of the symbolic model-checking procedure for real-time systems in (HNSY94).
To make H scYT scECH more efficient and effective, we designed and implemented model-checking strategies and abstract operators that can expedite the verification process. To enable H scYT scECH to verify nonlinear hybrid automata, we also introduce two translations from nonlinear hybrid automata to linear hybrid automata that can be fed into H scYT scECH for automatic analysis. We have applied H scYT scECH to analyze more than 30 hybrid-system benchmarks. In this dissertation, we show the application of H scYT scECH to three nontrivial hybrid systems taken from the literature.