Xiao, G. and Kontchakov, Roman and Cogrel, B. and Calvanese, D. and Botoeva, E. (2018) Efficient handling of SPARQL OPTIONAL for OBDA. In: Vrandečić, D. and Bontcheva, K. and Suárez-Figueroa, M.C. and Presutti, V. and Celino, I. and Sabou, M. and Kaffee, L.-A. and Simperl, E. (eds.) The Semantic Web – ISWC 2018 17th International Semantic Web Conference, Monterey, CA, USA, October 8–12, 2018, Proceedings, Part I. Lecture Notes in Computer Science 11136. Springer, pp. 354-373. ISBN 9783030006716.
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Abstract
OPTIONAL is a key feature in SPARQL for dealing with missing information. While this operator is used extensively, it is also known for its complexity, which can make efficient evaluation of queries with OPTIONAL challenging. We tackle this problem in the Ontology-Based Data Access (OBDA) setting, where the data is stored in a SQL relational database and exposed as a virtual RDF graph by means of an R2RML mapping. We start with a succinct translation of a SPARQL fragment into SQL. It fully respects bag semantics and three-valued logic and relies on the extensive use of the LEFT JOIN operator and COALESCE function. We then propose optimisation techniques for reducing the size and improving the structure of generated SQL queries. Our optimisations capture interactions between JOIN, LEFT JOIN, COALESCE and integrity constraints such as attribute nullability, uniqueness and foreign key constraints. Finally, we empirically verify effectiveness of our techniques on the BSBM OBDA benchmark.
Metadata
| Item Type: | Book Section |
|---|---|
| Additional Information: | 17th International Semantic Web Conference, Monterey, CA, USA, October 8–12, 2018, Proceedings, Part I. The final publication is available at Springer via the link above. |
| School: | Birkbeck Faculties and Schools > Faculty of Science > School of Computing and Mathematical Sciences |
| Depositing User: | Roman Kontchakov |
| Date Deposited: | 18 Sep 2018 09:25 |
| Last Modified: | 09 Aug 2023 12:44 |
| URI: | https://eprints.bbk.ac.uk/id/eprint/23954 |
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