Documentation and Examples

Quick update. He have re-organized the documentation section of the main site and of the technical wiki . Things should be much easier to find now.

We are also extending the "Examples" section with several of the scenarios that we use for testing, demonstration and benchmarking. We have already included the BSBM and FishMark scenarios that we use for benchmarks, and the IMDB-MovieOntology scenario that we use for demonstrations. Take a look at them, they are nice examples of very natural mappings.

The IMDB-MovieOntology scenario is particularly interesting since the database is real, very large and mappings turn out to be interesting. Take a look!

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.

Performance

• 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

Documentation

• Revised and extended all technical documentation

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

     http://ontop.inf.unibz.it/


Happy new year!
The -ontop- Team

Optique starts!

Last week we were in Oslo for the kick-off meeting of Optique. For those that don't know yet, Optique [1] is the EU project that will be funding research for and the development of -ontop- for the next 4 years.
The objective of the project (in simpler words that those used in the brochures) is to use semantic technology, with focus on reasoning and OBDA, to create an integrated solution that companies can use to regain control of their data. The keyword here is Big Data, big in volume of course, but also in diversity and speed.

The basic idea is that RDF, Ontology and OBDA can allow companies to perform complex data integration tasks in cheaper ways and through methodologies that will allow them to continue growing in a controlled way.

The consoritium is made by a great bunch of bright people, which are very much eager to deliver the promised results.

On the academic side the consortium includes of course the Free University  of Bolzano, but also University of Athens, Oxford University, Technical University of Hamburg, University of Oslo and Sapienza University of Rome.

On the industrial side things are also very exciting. Working on the integration of results and making a real product out of the things academic do we will have FuildOps, and specialised in the Statoil use case we will also have DNV. And something very exciting about the industry side is that we will have Siemens and Statoil too as providers for use cases, consumers and evaluators of the technology developed within the project. In both cases we are talking abouta huge number of data sources and ridiculous volumes of data.

What is extremely exciting about all this is that -ontop- and Quest are going to be central in achieving all this goals, we are all betting on efficient query rewriting and efficient execution. Because of that, we are getting funding of course and thanks to that we already grew the team from 2 people actively developing -ontop- to 4 people, and we will grow to 5 or 6 very soon. More over, we started already focusing a lot in things related to usability in order to be able to integrate with the tools from FluidsOp and to be ready to start providing results in the first months. Things are moving fast, and will move even faster in 2013.

In conclusion,  things are going to get really exciting in the OBDA are, so stay tuned!

[1] http://optique.project.ifi.uio.no/ (temporal website)

ISWC Demo tomorrow

Hi all,

Tomorrow we have a demo during ISWC (6:30 pm). If you want to take a look at what Quest can do in "virtual RDF" mode, come and visit us! I'll also talk about the techniques we use, the performance we get and the plans for the future.

Don't forget to vote for us!

- Mariano

Status update

A small status update.

The SPARQL 1.0 implementation is around 80% done, missing still support for some of the corner cases in nested OPTIONALs with references to upper level variables. The nice part is that Josef is almost done with all the core SPARQL functions, leaving little more to be done. Timea is also preparing the Sesame provider layer for Quest that will let us offer access to Quest through Sesame's console to setup a proper SPARQL end-point.

Also, even though we haven't fully finished the implementation it is already in a good state to cover most queries, so Mindaugas is setting up the environment for running the Berlin Benchmark. Expect some number comparing MySQL D2RQ, Virtuoso virtual RDF graphs and Quest (running on top of MySQL) very very soon.

Talking about benchmarks, the paper by Bail et al. [1] was accepted. They compare MySQL, Virtuoso virtual graphs and Quest in virtual RDF mode. Some great numbers for Quest, up to 500 times faster than Virtuoso, almost as fast as native MySQL. It seems that Virtuoso virtual graphs performance drops dramatically with each join you add to the queries, 4 queries already set Virtuoso to 20 or less queries per second (qps) when Quest and MySQL are on the hundreds (500-900). Five joins and we go down to 1 qps with virtuoso, with 550 qps for Quest and 840 qps for MySQL. The paper is available here [2].

Exciting times!

[1] Samantha Bail, Sandra Alkiviadous, Bijan Parsia, David Workman, Mark van Harmelen, Rafael S. Gonçalves, and Cristina Garilao. FishMark: A Linked Data Application Benchmark. SSWS, 2012. ISWC 2012 workshop. To appear.
[2] http://owl.cs.manchester.ac.uk/fishmark/

DAWG Tests for SPARQL 1.0

So, we finally finished the implementation of SPARQL 1.0! There is still some way to go, many edge cases need to be sorted out. However, it will be only 1 or 2 months and we will the first version fully compatible with SPARQL 1.0.

We are also already testing the Sesame Repository implementation, so expect some huge jump in functionality very very soon ;).

Teaser

Small teaser on the next build:

• First build with support for all the core features of SPARQL 1.0!! (unbound predicates, e.g.,  ?x rdf:type ?c, OPTIONAL, unbound variables through UNION, related filters: bound(), isIRI(), isLiteral())!
• Our first mapping assistant! Yes! at last some help in writing mappings in -ontopPro- (our plugin for Protege)! 
• Proper SQL null handling
• And a paper to describe the whole approach ;-)

Stay tunned! The next release is schedule in 5 weeks from today. If you can't wait, contact us to help us test and debug :D.