Flavius Frasincar Geert-Jan Houben Richard Vdovjak Peter Barna RAL: An Algebra for Querying RDF. 83-109 2004 7 World Wide Web 1 http://dx.doi.org/10.1023/B:WWWJ.0000015866.43076.06 db/journals/www/www7.html#FrasincarHVB04