Query rewriting under query refinements

Abstract

Ontologies expressed in description logics or extensions of datalog are gradually used for describing the domain of many research and industrial strength applications. They provide a formal semantically rich and data-independent layer over which user queries can be posed. A prominent technique for query answering in ontology-based applications is query rewriting, where the given user query Q and ontology O are transformed into a (datalog) program R that captures the answers of Q over O and every database D. In realistic scenarios it is quite often the case that users refine their original query by adding or removing constraints until they produce a final one. In such scenarios, however, all existing systems would compute a new rewriting Ri for each refined query Qi from scratch, discarding any information possibly computed previously. In this paper we study the problem of computing a rewriting for a query Q′ which is a “refinement” of a query Q by exploiting as much as possible information possibly computed previously for Q. We investigate whether such information is usable when computing a rewriting for Q′ and present detailed algorithms. Finally, we have implemented all proposed algorithms and conducted an extensive experimental evaluation.