Kyrie is a query rewriting system that uses an ontology to rewrite a Datalog query into an different Datalog query that captures the knowledge of the ontology. The rewritten query obtains extensionally from a data source the results (certain answers) that are extensionally or intensionally implied by the original query.

When no recursion is involved the rewritten Datalog query can be unfolded into a union of conjunctive queries, which can later be transformed to SQL or other languages, with other tools like Morph.

Kyrie started as a fork of REQUIEM. The focus for this system has been set on:

• improving rewriting times
• producing shorter queries when possible, since they should imply less computational load for systems accepting the rewritten queries.
• keeping the expressive logic ELHIO for the description of the ontology.

These objectives have been achieved as can be seen in the evaluation. The main publications related with this work are the following:

1. Mora, José and Corcho, Óscar. "Engineering optimisations in query rewriting for OBDA" I-SEMANTICS, 2013, 4-6 September 2013, Graz, Austria.
2. Mora, J. and Corcho, Oscar. (2013). Towards a systematic benchmarking of ontology-based query rewriting systems. The 12th International Semantic Web Conference (ISWC2013) (p./pp. 369--384), 21-26 October 2013, Sydney, Australia.