Wang Lian Nikos Mamoulis David W. Cheung A Filter Index for Complex Queries on Semi-structured Data. 397-408 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2762&spage=397 2003 conf/waim/2003 WAIM db/conf/waim/waim2003.html#LianMC03