Artem Katasonov Improving Usability of Location-Based Services with User-Centric Data Querying. 365-374 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3268&spage=365 2004 conf/edbtw/2004 EDBT Workshops db/conf/edbtw/edbtw2004.html#Katasonov04