Abstract
The RDF framework is becoming popular for presenting data. It makes the data easily accessible and queryable.
However, the most common way how to store structured data is to use a relational database system. It is essential to create a mapping between these two worlds, to publish the data stored in a relational database in the RDF format.
That can be effectively achieved by a virtual SPARQL endpoint over relational data. There are already existing tools providing virtual SPARQL endpoints, but as we will show in the paper there is still space for improvement.
In this paper we propose an algorithm to query RDF data stored in a relational database with an user defined mapping. Our aim is to generate SQL queries which can be effectively executed on the relational engines.
In comparison to existing approaches we do not rely only on the optimizations of the relational query, but the SPARQL query first.