SOFTWARE DEPENDABILITY MODELS UNDER MEMORY FAULTS WITH APPLICATION TOA DIGITAL SYSTEM IN NUCLEAR-POWER-PLANTS

In this work, software dependability under memory faults in the operat ional phase is predicted by two models: an analytic model and the stoc hastic activity network (SAN) model. The analytic model is based on th e simple reliability theory and the graph theory, which represents the software as a graph composed of nodes and arcs. Through proper transf ormation, the graph can be reduced to a simple two-node graph from whi ch software reliability can be derived. The SAN model permits the repr esentation of concurrency, timeliness, fault tolerance, and degradable performance of the system and provides a means for determining the st ochastic behavior of a software. Using these models, we predict the re liability of an application software in a digital system, Interposing Logic System (ILS), in a nuclear power plant and show the sensitivity of software reliability to major physical parameters which affect soft ware failure in the normal operation phase. It is found that the effec ts of hardware faults on software failure should be considered for the accurate prediction of software dependability in the operation phase. (C) 1998 Elsevier Science Limited.