A rigorous approach to availability modeling

Modeling and analyzing the dependability of software systems is a key activity in the development of embedded systems. An important factor of dependability is availability. Current modeling methods that support availability modeling are not based on a rigorous modeling theory. Therefore, when the behavior of the system influences the availability, as it is the case for fault-tolerant systems, the resulting analysis is imprecise or relies on external information. Based on a probabilistic extension of the Focus theory, we present a modeling technique that allows specifiying availability with a clear semantics. This semantics is a transformation of the original behavior to one that includes failures. Our approach enables modeling and verifying availability properties in the same way as system behavior.