Converging to the chase - A tool for finite controllability

We solve a problem, stated in [5], showing that Sticky Datalog∃, defined in the cited paper as an element of the Datalog± project, has the Finite Controllability property, which means that whenever a query Ψ is not logically implied by a set of atoms D and a Sticky Datalog∃ theory T a finite structure M can be found such that M⊨D,T, but M⊭Ψ. In order to do that, we develop a technique, which we believe can have further applications, of approximating Chase(T,D), for a database instance D and a set of tuple generating dependencies and Datalog rules T, by an infinite sequence of finite structures, all of them being models of T and D.