Rule Subsumption

A common programmer error is to leave out one or more clauses in the antecedent of a rule. This causes the rule to be over-broad in its application and may cause it to subsume other rules.

Example: SACON structural analysis consultant[ Bennett, J. S. and Engelmore, R. S., ``SACON: a Knowledge-based Consultant for Structural Analysis'', Proc. IJCAI-79, pp. 47-49, Morgan Kaufmann Publishers.]

If: 1) The analysis error (in percent) that is 
       tolerable is less than 5, and
    2) The non-dimensional stress of the 
       substructure is greater than .5, and 
    3) The number of cycles the loading is to be 
       applied is greater than 10000
Then: It is definite (1.0) that fatigue is a 
       phenomenon ...
A rule like this one, but without antecedent clause (3), was included. The bad rule subsumed this rule and two others (stress > .7, cycles > 1000; stress > .9, cycles > 100) with the same conclusion.

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