Diagnosis is the task of determining whether a system is behaving correctly and, if not, identifying the failing component or type of fault. In AI and automated reasoning, diagnostic methods use observations of system behavior to infer likely causes of errors or malfunctions.
Concerned with the development of algorithms and techniques that are able to determine whether the behaviour of a system is correct. If the system is not functioning correctly, the algorithm should be able to determine, as accurately as possible, which part of the system is failing, and which kind of fault it is facing. The computation is based on observations, which provide information on the current behaviour.