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Negation as Failure

Keywords: Micro-PLANNER, closed world assumption, rule of inference

Categories: Logic Programming


Author(s): Martin Merry

Negation as failure is a rule of inference which allows one to deduce that NOT P is true if all possible proofs of P fail. This is the way that negation is treated in Prolog and Micro-PLANNER. When using a system for database access, the assumption that negation as failure corresponds to true negation is precisely a consequence of the closed world assumption, i.e., the assumption that all relevant information is contained in the database. Without the closed world assumption, negation as failure corresponds to `we assume something is false if we cannot deduce it from available information', which is not the same as true negation. Negation as failure is an example of Default Reasoning. Its mathematical meaning is extremely questionable.


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