Stavros Papadopoulos Dimitris Sacharidis Kyriakos Mouratidis Continuous Medoid Queries over Moving Objects. 38-56 2007 conf/ssd/2007 SSTD http://dx.doi.org/10.1007/978-3-540-73540-3_3 db/conf/ssd/sstd2007.html#PapadopoulosSM07