# Negation as Failure

### Keith L. Clark

## Reduced Abstract

A query evaluation process for a logic data base comprising a set of clauses is described. Its is essentially a Horn clause theorem prover augmented wih a special negation as failure inference rule whereby ~P can be inferred if every possible proof of P fails. We show how the rule only allows us to conclude negated facts that could be inferred from the completed date base, a data base of relation defintions and equality schemas that we consider is implicitly given by the data base of clauses.
KEYWORDS: Completed data base, equality theory

First Published in: Logic and Data Bases, (eds Gallaire and Minker), 1978.

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