Marcel Karnstedt Kai-Uwe Sattler Michael Haß Manfred Hauswirth Brahmananda Sapkota Roman Schmidt Estimating the number of answers with guarantees for structured queries in p2p databases. 1407-1408 2008 CIKM http://doi.acm.org/10.1145/1458082.1458304 conf/cikm/2008 db/conf/cikm/cikm2008.html#KarnstedtSHHSS08