Philip S. Yu Kun-Lung Wu Shyh-Kwei Chen Monitoring Continual Range Queries. 1-12 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3007&spage=1 2004 conf/apweb/2004 APWeb db/conf/apweb/apweb2004.html#YuWC04