Leopoldo E. Bertossi Loreto Bravo Query Answering in Peer-to-Peer Data Exchange Systems. 476-485 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3268&spage=476 2004 conf/edbtw/2004 EDBT Workshops db/conf/edbtw/edbtw2004.html#BertossiB04