A method for the synthesis of controllers to handle safety, liveness, and real-time constraints

This paper describes a synthesis method that automatically derives controllers for timed discrete-event systems with nonterminating behavior modeled by timed transition graphs and specifications of control requirements expressed by metric temporal logic (MTL) formulas. Synthesis is performed by using 1) a forward-chaining search that evaluates the satisfiability of MTL formulas over sequences of states generated by occurrences of actions and 2) a control-directed backtracking technique that takes into consideration the controllability of actions. This method has several interesting features. First, the issues of controllability, safety, liveness, and real time are integrated in a single framework, Second, the synthesis process does not require explicit storage of an entire transition structure over which formulas are checked and can be stopped at any moment, giving an approximate but useful result. Third, search and control mechanisms allow circumvention of the state explosion problem.