faultmodel

A fault model is an abstraction that describes the set of faults that can affect a system, used to study, test, and improve reliability and fault tolerance. It specifies which components may fail, how failures manifest, when they occur, and how the observable behavior of the system is affected. By formalizing likely failure modes, a fault model supports risk assessment, design decisions, and the planning of detection, containment, and recovery strategies.

In hardware and digital systems, common fault models include stuck-at faults (a line is fixed at logical 0 or 1), bridging faults (shorts between lines), open or short faults in connections, and delay or transition faults that affect timing. Fault models may distinguish between transient (temporary) and permanent faults. These models guide test generation and diagnosis, enabling efficient verification of circuit correctness and robustness.

In software engineering, fault models describe potential software faults and failures, such as thrown exceptions, crashes, resource leaks, data corruption, or timing violations. Fault injection uses these models to simulate failures and evaluate system resilience, recovery mechanisms, and reliability metrics. Mutation testing is a related approach that uses controlled fault models to assess the effectiveness of test suites.

Creating a fault model involves identifying plausible failure modes, estimating their impact and likelihood, and defining detectable symptoms and measurable effects. Models should be validated with field data and updated as systems evolve, balancing realism with tractability to guide testing and fault-tolerance design.