Beschreibung:
<jats:p>
Ontological queries are evaluated against a database combined with ontological constraints. Answering such queries is a challenging new problem for database research. For many ontological modelling languages, query answering can be solved via query rewriting: given a conjunctive query and an ontology, the query can be transformed into a first-order query, called the
<jats:italic>perfect rewriting</jats:italic>
, that takes into account the semantic consequences of the ontology. Then, for every extensional database
<jats:italic>D</jats:italic>
, the answer to the query is obtained by evaluating the rewritten query against
<jats:italic>D.</jats:italic>
In this paper we present a new algorithm that computes the perfect rewriting of a conjunctive query w.r.t. a linear Datalog
<jats:sup>±</jats:sup>
ontology. Also, we provide an experimental comparison of our algorithm with existing rewriting techniques.
</jats:p>