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Hydrowl • A Hybrid Query Answering System for OWL 2 DL Ontologies


Hydrowl is a prototype tool for answering conjunctive queries over data whose semantics have been described using the OWL 2 DL ontology language. Hence, in Semantic Web and Description Logic jargon Hydrowl is a system for ontology-based data access.

Hydrowl is based on novel hybrid techniques which attempt to combine many existing Semantic Web technologies in an effort to deliver scalable query answering over very expressive fragments of OWL 2 DL. Hence, it does not assume that expressivity is restricted to one of the known tractable profiles (e.g., OWL 2 QL), but it tries to tackle arbitrary OWL 2 DL ontologies.

In particular Hydrowl uses, on the one hand, scalable data management systems like OWL 2 RL reasoners (current version uses OWLim) and, on the other hand, heavy-weight fully-fledged OWL 2 DL and OWL 2 EL systems (current version uses HermiT and Rapid, respectively). Since OWL 2 RL systems are most likely incomplete when presented with an OWL 2 DL ontology (they won't compute all the answers to a user query), the heavy-weight systems are used to help them retrieve those answers that they would otherwise miss. The heavy-weight systems are mostly used at off-line pre-processing steps, while at run-time Hydrowl is mainly using OWLim.

Hydrowl is not strongly tied to the aforementioned systems and any combination of OWL 2 RL, OWL 2 EL, and OWL 2 DL systems is possible.

For more details about the theory behind Hydrowl please see the list of publications.



Hydrowl is available under the GNU Affero General Public License. The latest version is Hydrowl 0.3. For past versions browse through here.


  Giorgos Stoilos
Hydrowl: A Hybrid Query Answering System for OWL 2 DL Ontologies [CONFERENCE]
In Proceedings of the 8th International Conference on Web Reasoning and Rule Systems (RR 2014), Athens, Greece.
[.pdf | .bib]
  Giorgos Stoilos and Giorgos Stamou
Hybrid Query Answering Over OWL Ontologies [CONFERENCE]
In Proceedings of the 21st European Conference on Artificial Intelligence (ECAI 2014), 2014.
[.pdf | .bib]
  Giorgos Stoilos
Ontology-Based Data Access Using Rewriting, OWL 2 RL reasoners, and Repairing
In Proceedings of the 11th European Semantic Web Conference (ESWC 2014), 2014.
[.pdf | .bib]



Hydrowl is currently being developed by Giorgos Stoilos.


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