  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.
