Sandro Daniel Camillo Carlos A. Heuser Ronaldo dos Santos Mello Querying Heterogeneous XML Sources through a Conceptual Schema. 186-199 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2813&spage=186 2003 conf/er/2003 ER db/conf/er/er2003.html#CamilloHM03