Abstract
Deductive database systems, that is, database systems with a query language based on logical rules must allow negated subgoals in rules to express an adequate range of queries. Adherence to classical deductive logic rarely offers the intuitively correct meaning of the rules. Thus, a variety of approaches to defining the right meaning of such rules have been developed. In this paper we survey the principal approaches including stratified negation, well-founded negation, stable-model semantics, and modularly stratified semantics.
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