A cost-effective and flexible scheme for software fault tolerance

A new software fault tolerance scheme, called the Self-Configuring Optimistic Programming scheme, (SCOP), is proposed. It attempts to reduce the cost of fault tolerant software by providing designers with a flexible redundant system component by which reliability and effectiveness can be dynamically combined. SCOP is based on comparisons of results produced by the variants, delivers resu1ts which are judged correct with the required probability, and is structured in phases in order to release such results as soon as available. It can be parameterized with respect to both the desired reliability and the desired response time. SCOP thus allows a trade-off between various attributes of system services (such as reliability, throughput and response time) in a desired manner. In offering this choice, SCOP also tries to minimize resource usage and is thus a flexible and cost-effectÌve tool for gracefully degradable systems.