Abstract
The expressive power of the family wILOG (⌝) of relational query languages is investigated. The languages are rule based, with value invention and stratified 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 first show that, in presence of value invention, the class of stratified programs made of two strata has the expressive power of the whole family, thus expressing the computable queries. We then show that the language wILOG ≠ of programs with nonequality and without negation expresses the mono- tone computable queries, and that the language wILOG 1/2, ⌝ of semipositive programs expresses the semimonotone computable queries.
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