SEMANTICS OF STATE-EVENTS IN HYBRID LANGUAGES

The semantics of a state-event statement is considered in a situation where one process changes the value of a variable, and another process executes a state-event statement - involving the same variable - at the same time-point. If the condition of the state-event statement is evaluated immediately, the shared variable may still have its old value. By means of an example model of a multi-section conveyor it is shown that immediate evaluation of state-event conditions is undesirable from a modelling point of view. The proposed semantics of the state-event statement is that the evaluation of the state-event condition is postponed until the other processes can no longer execute statements at the current time-point, and a new consistent state has been established. This semantics facilitates the development of correct models. The proposed semantics is analogous to the transition semantics in hybrid automata.