The duality of fault-tolerant system structures

An examination of the structure of fault-tolerant systems incorporating backward error recovery indicates a partitioning into two broad classes. Two canonical models, each representing a particular class of systems, have been constructed. The first model incorporates objects and actions as the entities for program construction whereas the second model employs communicating processes and conversations. Applications in areas such as office information and banking systems are typically described and built in terms of the first model whereas applications in the area of process control are usually described and built in terms of the second model. The paper claims that the two models are duals of each other and presents arguments and examples to substantiate this claim. It will be shown that the techniques that have been developed within the context of one model turn out to have interesting and hitherto unexplored duals in the other model.