To Normalize the Relationship between the Certainty Factor

In this paper, we prove that the EMYCIN formula for the sequential propagation can be derived strictly from the deenition of the certainty factor according to probability theory. Some researchers think that this combination formula is inconsistent with the deenition of certainty factor in the sense of probability theory. This was not correct. Moreover, under the condition that there exists no need for prior probabilities to be supplied with values, we reformulate the parallel propagation from the deenition of the certainty factor according to probability theory. Therefore, the paper normalizes the relationship between the deenition of the certainty factor and combination formulae for sequential and parallel propagations. In conclusion, this paper demonstrated that the certainty factor model can be built on the foundation of probability theory.