[DL] -ontop- SPARQL over ontologies and databases - New release, v1.7alpha-b2039

[Mariano Rodriguez]

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.

This upgrade includes bug fixes, major improvements to existing
features and many new and exciting features including:

SPARQL 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.
 * New benchmarks. 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

SPARQL query answering in -ontop- is done by means of SPARQL-to-SQL
translations. The SQL query generated by -ontop- is executed directly
at the DBMS, with no data moving back and forth. Moreover, the system
uses a variety of techniques (e.g., query rewriting, partial
evaluation, query containment, SQL analysis, virtual RDF graph
completion) to generate minimal and 'lean' SQL queries that can be
planned and executed efficiently by open source and commercial DBMS
alike.

The framework is still in alpha and has several rough edges, however,
given the performance it is currently able to deliver we think it
might be interesting to give it a test drive. The system is available
at

      http://ontop.inf.unibz.it/

The -ontop- development team