Millist W. Vincent Jixue Liu Chengfei Liu Redundancy Free Mappings from Relations to XML. 55-67 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2762&spage=55 2003 conf/waim/2003 WAIM db/conf/waim/waim2003.html#VincentLL03