Alexandros Nanopoulos Panayiotis Bozanis Categorical Range Queires in Large Databases. 122-139 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2750&spage=122 2003 conf/ssd/2003 SSTD db/conf/ssd/sstd2003.html#NanopoulosB03