Abstract
In this paper we study the extension of description logics of the extit{DL-Lite} family with singleton nominals, which correspond in OWL~2 to the ObjectHasValue construct. Differently from arbitrary (non-singleton) nominals, which make query answering intractable in data complexity, we show that both knowledge base satisfiability and conjunctive query answering stay first-order rewritable when extit{DL-Lite}{$_A$} is extended with singleton nominals. Our technique is based on a practically implementable algorithm based on rewriting rules, in the style of those implemented in current state-of-the-art OBDA systems based on extit{DL-Lite}, such as QuOnto and Quest. This allows us to follow the tradition of the extit{DL-Lite} family for employing relational database technology for query answering with optimal data complexity.