Formal Definition of Program Faults and Hierarchy of Program Fault-Tolerant Abilities

These two issues are addressed in this paper: 1) the formal definitions of the concepts relevant to program faults, and 2) the comparison and classification of program faulttolerant abilities. We firstly analyze the subtle differences among these basic concepts: faults, errors and failures, and represent their formal definitions by using the state-based theory of program behavior; and then we propose a hierarchy for software fault-tolerant abilities from the aspect of satisfaction of safety and liveness properties. The main purpose of this work is to facilitate an accurate understanding of basic concepts and classifying of fault-tolerant abilities of different approaches in a systematic way.