On the Power of Stratified Logic Programs with Value Invention for Expressing Database Transformations

. The expressive power of the family of ILOG (:) languages is investigated. The languages are rule based, with value invention and stratified negation. The chosen semantics for value invention is based on Skolem functor terms. We show that, in presence of value invention, the whole expressive power is achieved using programs made of two strata, and that ILOG 6= (i.e., the class of programs with non-equality and without negation) express the downward monotone list constructive transformations. 1 Introduction The study of query languages is a major issue in database theory. Departing from relational calculus and algebra for the relational model of data [8], several extensions to both the languages and model have been investigated, mainly with the goal of gaining in expressive power. The criterion of genericity has been widely accepted to limit the class of "interesting" queries to those that do not interpret values, i.e., for which the only significant relationships among data are ..