Using Architectural Properties to Model and Measure Graceful Degradation

System-wide graceful degradation may be a viable approach to improving dependability in computer systems. In order to evaluate and improve system-wide graceful degradation we present a system model that will explicitly define graceful degradation as a system property, and measure how well a system gracefully degrades in the presence of multiple combinations of component failures. The system's software architecture plays a major role in this model, because the interface and component specifications embody the architecture's abstraction principle. We use the architecture to group components into subsystems that enable reasoning about overall system utility. We apply this model to an extensive example of a distributed embedded control system architecture to specify the relative utility of all valid system configurations. We then simulate working system configurations and compare their abihty to provide functionality to the utility measures predicted by our model.