Implementing fault tolerance with an attribute and functional based model

Programs constructed using techniques that allow software or operational faults to be tolerated are typically written using an imperative computational model. Here, an alternative is described in which such programs are written using an attribute and functional based model called FTAG. The basic model is introduced, followed by a description of mechanisms that allow a variety of standard fault tolerance techniques to be realized in a straightforward way. Techniques that can be accommodated include replication and checkpointing to tolerate operational faults, and recovery blocks and N-version programming to tolerate software faults. Several examples are given to illustrate these techniques, including a replicated name server and a fault-tolerant sort that uses recovery blocks. These examples also serve to highlight the advantages of FTAG when compared to traditional imperative approaches, such as a declarative style, separation of semantic and syntactic definitions and the simplicity of a functional foundation. Finally an outline of how this model can be implemented in a computer system containing multiple processors is given.<>