Rajeev Motwani Rina Panigrahy Ying Xu 0002 Estimating Sum by Weighted Sampling. 53-64 2007 conf/icalp/2007 ICALP http://dx.doi.org/10.1007/978-3-540-73420-8_7 db/conf/icalp/icalp2007.html#MotwaniPX07