Abstract
In this paper we present practical algorithms for query answering and knowledge base satisfiability checking in DL-Lite (HN) horn, a logic from the extended DL-Lite family that contains horn concept inclusions and number restriction. This logic is the most expressive DL that is shown to be FOL-rewritable. The algorithms we present are based on the rewriting technique so that reasoning over the TBox and over the ABox can be done independently of each other, and the inference problems are reduced to first order query evaluation. This allows for employing relational database technology for the final query evaluation and gives optimal data complexity.