certainty factor

views updated

certainty factor A device used in rule-based systems to assign weight to facts or pieces of knowledge. The weights express the perceived certainty of a fact being true: usually –1 indicates certainly false, +1 indicates definitely true, and intermediate values represent varying degrees of certainty, with 0 meaning unknown. The medical expert system MYCIN used certainty factors, with conjunctions of rules taking the minimum value. The use of certainty factors is similar to probabilistic reasoning but is less formally related to probability theory.