Belief Models and Certainty Factors

This approach has been suggested by Shortliffe and Buchanan and used in their famous medical diagnosis MYCIN system.

MYCIN is essentially and expert system. Here we only concentrate on the probabilistic reasoning aspects of MYCIN.

• MYCIN represents knowledge as a set of rules.
• Associated with each rule is a certainty factor

• A certainty factor is based on measures of belief B and disbelief D of an hypothesis given evidence E as follows:

  
  
  

  where is the standard probability.

• The certainty factor C of some hypothesis given evidenceE is defined as:
  
  

 
• Reasoning with Certainty factors
• Overcoming the Bayes Rule shortcomings