Diagnoses as Coherent Assumption Sets

Oskar Dressler Siemens ZFE IS INF 22 Otto-Hahn-Ring 6 8 Mi~nchen 83, West-Germany E-mail: dressler@ztivax.siemens.com Model-based diagnosis can be viewed as the task of assigning modes of behavior to the components of a device. Mode assignments must "match" what has been reported about the device: initial values and measurements taken during the diagnostic process. In the simplest case the behavior of a component can be ei ther normal or abnormal. Because of this a diagnosis can be characterized as a subset of the components that is assigned the abnormal mode. For the rest of the components the normal mode is assigned. The overall assignment must "match". There are several ways for giving a precise meaning to "match", The least restrictive is the consistency-based definition. A diagnosis is a mode assignment that is consistent with the observations.