Ahmed Metwally Divyakant Agrawal Amr El Abbadi Efficient Computation of Frequent and Top-k Elements in Data Streams. 398-412 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3363&spage=398 2005 conf/icdt/2005 ICDT db/conf/icdt/icdt2005.html#MetwallyAA05