Jan Zemánek Simon Schenk Optimizing SPARQL Queries over Disparate RDF Data Sources through Distributed Semi-Joins. 2008 International Semantic Web Conference (Posters & Demos) http://ceur-ws.org/Vol-401/iswc2008pd_submission_69.pdf conf/semweb/2008p db/conf/semweb/iswc2008p.html#ZemanekS08