Efficient SPARQL-to-SQL translation using R2RML Mappings Mariano Rodriguez-Muro, Martin Rezk, Josef Hardi, Mindaugas Slusnys Timea Bagosi and Diego Calvanese KRDB Research Centre, Free University of Bozen-Bolzano {rodriguez,mrezk, josef.hardi, mindaugas.slusnys, timea.bagosi, calvanese}@inf.unibz.it