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Syntax and Consistent Equation Semantics of Hybrid Chi

D.A. van Beek, K.L. Man, M.A. Reniers, J.E. Rooda, R.R.H. Schiffelers

The hybrid Chi formalism integrates concepts from dynamics and control theory with concepts from computer science, in particular from process algebra and hybrid automata. It integrates ease of modeling with a straightforward, structured operational semantics. Its `consistent equation semantics' enforces state changes to be consistent with invariants as in most hybrid automata. Ease of modeling is ensured by means of the following concepts: 1) different classes of variables: discrete and continuous, of subclass jumping or non-jumping, and algebraic; 2) strong time determinism of alternative composition in combination with delayable guards; 3) integration of urgent and non-urgent actions; 4) differential algebraic equations as a process term as in mathematics; 5) steady-state initialization; and 6) several user-friendly modeling extensions. Furthermore, the Chi language incorporates several concepts for complex system specification: 1) process terms for scoping that integrate abstraction, local variables, local channels and recursion definitions; 2) process definition and instantiation that enable process re-use, encapsulation, hierarchical and/or modular composition of processes; and 3) different interaction mechanisms: handshake synchronization and synchronous communication for discrete-event processes that do not share variables, and shared variables for continuous-time processes. The syntax and semantics are illustrated using many different examples. Furthermore, general translations from hybrid automata and PWA systems to Chi are given.

Journal of Logic and Algebraic Programming, special issue on hybrid systems, vol. 68, no. 1-2, 129-210, 2006.

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