The Expressive Power of Stratified Logic Programs with Value Invention

The expressive power of the family wILOG of relational query languages is investi gated The languages are rule based with value invention and strati ed negation The semantics for value invention is based on Skolem functor terms We study a hierarchy of languages based on the number of strata allowed in programs We rst show that in presence of value invention the class of strati ed programs made of two strata has the whole expressive power of the family thus expressing the computable queries We then show that the language wILOG of programs with non equality and without negation ex presses the monotone queries and that the language wILOG of semipositive programs expresses the semimonotone queries