Construction and stepwise refinement of dependability models

This paper presents a stepwise approach for dependability modeling, based on generalized stochastic Petri nets (GSPNs). The first-step model called functional-level model, is built based on the system’s functional specifications and then completed by the structural model as soon as the system’s architecture is known. It can then be refined according to three complementary aspects: component decomposition, state and event fine-tuning and distribution adjustment to take into account increasing event rates. We define specific rules to make the successive transformations as easy and systematic as possible. This approach allows the various dependencies to be taken into account at the right level of abstraction: functional dependency, structural dependency and those induced by non-exponential distributions. A part of the approach is applied to an instrumentation and control (I&C) system in power plants.