Dan Olteanu Tim Furche François Bry Evaluating Complex Queries Against XML Streams with Polynomial Combined Complexity. 31-44 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3112&spage=31 2004 conf/bncod/2004 BNCOD db/conf/bncod/bncod2004.html#OlteanuFB04