FTAG: A Functional and Attribute Based Model for Writing Fault-Tolerant Software

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 a functional and attribute based model called FTAG (Fault-Tolerant Attribute Grammars). The basic model is introduced first, 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. A formal description of FTAG that precisely specifies the semantics of the model is also presented. Finally, a software architecture describing how FTAG can be implemented in a computer system containing multiple processors is given.