On-Line Diagnosis of Unrestricted Faults

A formal model for the study of on-line diagnosis is introduced and used to investigate the diagnosis of unrestricted faults. Within this model a fault of a system S is considered to be a transformation of S into another system S' at some time r. The resulting faulty system is taken to be the system which looks like S up to time r and like S' thereafter. Notions of fault tolerance and error are defined in terms of the resulting system being able to mimic some desired behavior as specified by a system S. A notion of on-line diagnosis is formulated which involves an external detector and a maximum time delay within which every error caused by a fault in a prescribed set must be detected.