Abstract: Variables associated with hypotheses of a qualitative physics model are grouped into type I variables and type II variables, wherein any possible value measured for a type I variable is guaranteed to render at least one hypothesis inconsistent and some, but not all, possible values measured for a type II variable will render at least one hypothesis inconsistent. A test score, indicating the desirability of observing a variable, is calculated for each variable and the type I variable with the highest test score is chosen for observation unless no type I variables have a test score above a predetermined threshold, in which case the type II variable with the highest test score is chosen.

Abstract: A set of confluences is deemed to be inconsistent by determining that there exists no set of values that can be assigned to all unknown variables of the confluences which result in a consistent set of predictions. Values are iteratively assigned to variables until either all unknown variables have been assigned a value or until a determination is made that no value of a particular variable will result in a consistent set of predictions. Values are assigned first to variables which appear in confluences having only two unknowns and then said values are propagated through the confluences of the hypothesis.

Abstract: A Qualitative Reasoning System (QRS) performs machine failure isolation by generating a plurality of pending hypotheses which assume the failure of one or more machine components and by testing each of the hypotheses by propagating actual values for machine parameters through confluence equations for the hypothosis being tested. Hypotheses which produce an inconsistent set of predictions are discarded while hypotheses which produce a consistent set of predictions are saved. The hypotheses are generated using a model instance data element which contains a qualitative physics model description of the machine. The machine failure is isolated when all but one hypothesis, which assumes the failure of one or more elementary machine components, remains.