Formal Verification of Diagnosability via Symbolic Model Checking Alessandro Cimatti Charles Pecheur Roberto Cavada ITC-irst RIACS/NASA Ames Research Center ITC-irst Povo, Trento, Italy Moffett Field, CA, U.S.A. Povo, Trento, Italy mailto:
[email protected] [email protected] [email protected] Abstract observed system. We propose a new, practical approach to the verification of diagnosability, making the following contribu• This paper addresses the formal verification of di• tions. First, we provide a formal characterization of diagnos• agnosis systems. We tackle the problem of diagnos• ability problem, using the idea of context, that explicitly takes ability: given a partially observable dynamic sys• into account the run-time conditions under which it should be tem, and a diagnosis system observing its evolution possible to acquire certain information. over time, we discuss how to verify (at design time) Second, we show that a diagnosability condition for a given if the diagnosis system will be able to infer (at run• plant is violated if and only if a critical pair can be found. A time) the required information on the hidden part of critical pair is a pair of executions that are indistinguishable the dynamic state. We tackle the problem by look• (i.e. share the same inputs and outputs), but hide conditions ing for pairs of scenarios that are observationally that should be distinguished (for instance, to prevent simple indistinguishable, but lead to situations that are re• failures to stay undetected and degenerate into catastrophic quired to be distinguished. We reduce the problem events). We define the coupled twin model of the plant, and to a model checking problem.