Rule-Based Expert Systems[Shortliffe, E. Computer-based medical consultations: MYCIN. New York: Elsevier, 1976.]

MYCIN diagnoses infectious blood diseases using a backward-chained (exhaustive) control strategy.

The algorithm, ignoring certainty factors, is basically backchaining:


  1. list of diseases, Goal-list
  2. initial symptoms, DB
  3. Rules

For each g &isin Goal-list do
If prove(g, DB, Rules) then Print (``Diagnosis:'', g)

Function prove (goal, DB, Rules)
If goal &isin DB then return True
elseif &exist r &isin Rules such that rRHS contains goal
then return provelist(LHS, DB, Rules)[provelist calls prove with each condition of LHS]
else Ask user about goal and return answer

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