Tractable Recursion over Geometric Data

We study the issue of adding a recursion operator to constraint query languages for linear spatial databases. We introduce a language with a bounded inflationary fixpoint operator which is closed and captures the set of polynomial time computable queries over linear constraint databases. This is the first logical characterization of the class of PTIME queries in this context. To prove the result, we develop original techniques to perform arithmetical and geometric operations with constraints. Work supported in part by TMR Project Chorochronos. Work supported by Inria, FNRS and ULB.