Fen Xia Tie-Yan Liu Jue Wang Wensheng Zhang 0002 Hang Li Listwise approach to learning to rank: theory and algorithm. 1192-1199 2008 ICML http://doi.acm.org/10.1145/1390156.1390306 conf/icml/2008 db/conf/icml/icml2008.html#XiaLWZL08