paper

Rewriting Ontological Queries into Small Nonrecursive Datalog Programs

arXiv:1106.3767

Abstract

We consider the setting of ontological database access, where an Abox is given in form of a relational database D and where a Boolean conjunctive query q has to be evaluated against D modulo a Tbox T formulated in DL-Lite or Linear Datalog+/-. It is well-known that (T,q) can be rewritten into an equivalent nonrecursive Datalog program P that can be directly evaluated over D. However, for Linear Datalog? or for DL-Lite versions that allow for role inclusion, the rewriting methods described so far result in a nonrecursive Datalog program P of size exponential in the joint size of T and q. This gives rise to the interesting question of whether such a rewriting necessarily needs to be of exponential size. In this paper we show that it is actually possible to translate (T,q) into a polynomially sized equivalent nonrecursive Datalog program P.

A shorter version is presented at the 24th International Workshop on Description Logics, DL 2011, Barcelona, Spain, July 13-16, 2011. The present version mainly extends the proof of Theorem 1 in Section 3. We plan to post further extended versions of this paper in the near future

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