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Knowledge-Based Validity Maintenance for Production Systems

In many problem domains, an action may be taken by an expert, which, due to new inferences or a changing domain situation, should be retracted. To this end, an effective problem solver will need to use some kind of validity-maintenance system, so that it can gracefully recover from invalid previous decisions. 
 
Unfortunately, the standard IF/THEN paradigm often used to encode expert behavior does not readily allow the expression and processing of this validity knowledge. We present a new extension to that rule paradigm which can be used to augment production-rule-based systems with validity maintenance capabilities, and demonstrate a straightforward algorithm for its interpretation.