Decentralized Diagnosis of Event-Driven Systems for Safely Reacting to Failures

In this paper, we extend the notion of safe-diagnosability (Paoli & Lafortune, 2003) to the decentralized setting by formulating the notion of safe-codiagnosability. Safe-codiagnosability requires that when the system executes a trace that is faulty, there exists at least one diagnoser that can detect this within bounded delay and also before the safety specification is violated. The notion of safe-diagnosability may also be viewed as an extension of the notion of codiagnosability. We show that safe-codiagnosability is equivalent to codiagnosability together with “zero-delay codiagnosability” of “boundary safe traces”. An algorithm of polynomial complexity is given for verifying safe-codiagnosability. For a safe-codiagnosable system, the same methods as those proposed in (Qiu & Kumar, 2004) can be applied for off-line synthesis of individual diagnosers, as well as for on-line diagnosis.