Monday, December 24, 2012

New build available! Tons of new features!

We are happy to announce the availability of a new build 2039 of -ontop- v1.7-alpha, a Java framework to query RDFS/OWL2QL ontologies with mappings to databases. The SPARQL engine, Quest, implements the latests techniques in SPARQL-to-SQL rewriting, produces very fast SQL queries and supports inference out of the box.

The framework is still in alpha and has several rough edges, however, given the performance it is currently able to deliver, and that many features are already stable, we think it might be interesting to give it a test drive. Please help us improve the stability of the build and bring it to beta grade and report any issues you encounter, we'll take all your feedback into account for the next release.

This upgrade includes bug fixes, major improvements to existing features and many new and exciting features. Some of the highlights of this build include:

SPARQL 1.0 support:

  • Support for most SPARQL built in functions, e.g., arithmetics, type checking, etc.
  • Support for CONSTRUCT and DESCRIBE result forms.
  • Support for OPTIONAL and bound, which allow you to have NEGATION in the usual SPARQL 1.0 style.
  • Support for variables in ANY position, e.g., to allow queries such as SELECT ?p ?v WHERE { ?x :name "John Smith". ?x ?p ?v }
  • Stronger compliance to standard RDF and SPARQL semantics for FILTER expressions.


  • Multiple improvements to the SPARQL-to-rule translation, mapping and TBox optimization algorithms.
  • New algorithm for query rewriting w.r.t. the TBox that increases the performance of query answering by many orders of magnitude when inference w.r.t. to existential constants is enabled. The implementation has been contributed by Dr. Roman Kontchakov.
  • Benchmarks. We finally started work on benchmarking. We tested against Virtuoso triple store, Virtuoso RDF views and D2R Server using the BSBM and FishMark benchmarks. The results show that Quest's query answering technique for 'virtual RDF graphs' can outperform these systems, in some cases by several orders of magnitude even when using an open source database as the backend. 

APIs and Accessibility

  • Completely new Sesame API provider, now users of Sesame can create "Virtual RDF repositories" with -ontop-.
  • SPARQL end-point support through integration with Sesame's workbench.

Mapping language

  • Improved support for default literal types, now it conforms with the R2RML "Natural Mapping" specification.
  • Support for language tags obtained from the DB
  • Proper support for constants in the mappings
  • Proper internal handling of NULL values in the database (as recommended by the R2RML standard)

Database support

  • Restored support for Oracle, DB2 and SQL Server
  • Improved support and performance over MySQL


  • Revised and extended all technical documentation

The new build can be downloaded from our brand new website:

Happy new year!
The -ontop- Team

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