Rewriting Ontological Queries into Small Nonrecursive Datalog Programs

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 T-box Σ formulated in DLLite or Linear Datalog± . It is well-known that (Σ, 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 Σ 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 (Σ, q) into a polynomially sized equivalent nonrecursive Datalog program P.

• Type: Journal
• Year: 2011
• Where: CORR
• Authors: Georg Gottlob, Thomas Schwentick
• Keywords: CORR 2011, Education, Equivalent Nonrecursive Datalog, Linear Datalog±, Nonrecursive Datalog Program