Synthesizing Masking Fault-Tolerant Systems from Deontic Specifications

In this paper, we study the problem of synthesizing faulttolerant components from specifications, i.e., the problem of automatically constructing a fault-tolerant component implementation from a logical specification of the component, and the system’s required level of fault-tolerance. We study a specific level of fault-tolerance: masking tolerance. A system exhibits masking tolerance when both the liveness and the safety properties of the behaviors of the system are preserved under the occurrence of faults. In our approach, the logical specification of components is given in dCTL, a branching time temporal logic with deontic operators, especially designed for fault-tolerant component specification. The synthesis algorithm takes the component specification, and automatically determines whether a component with masking fault-tolerance is realizable, and the maximal set of faults supported for this level of tolerance. Our technique for synthesis is based on capturing masking fault-tolerance via a simulation relation. Furthermore, a combination of an extension of a synthesis algorithm for CTL to cope with dCTL specifications, with simulation algorithms, is defined in order to synthesize masking fault-tolerant implementations.