Orthogonal Fault Tolerance for Dynamically Adaptive Systems

In dynamic systems that adapt to users’ needs and changing environments, dependability needs cannot be avoided. This paper proposes an orthogonal fault tolerance model as a means to manage and reason about multiple fault tolerance mechanisms that co-exist in dynamically adaptive systems. One of the key challenges associated with dynamically evolving fault tolerance needs is the feature interaction problem arising from the integration of fault tolerance features. The proposed approach provides a separation of fault tolerance concerns to study the effects of integrated fault tolerance on the system. This approach uses state machine and operational semantics to reason about these interactions and inconsistencies. The proposed approach is supported by the tool NuSMV to simulate and verify the state machines against logic statements. Keywords—dynamically adaptive systems; fault tolerance; orthogonal fault tolerance;