Jonathan Hayes Claudio Gutiérrez Bipartite Graphs as Intermediate Model for RDF. 47-61 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3298&spage=47 2004 conf/semweb/2004 International Semantic Web Conference db/conf/semweb/iswc2004.html#HayesG04