Shengliang Xu Shenghua Bao Yunbo Cao Yong Yu Using social annotations to improve language model for information retrieval. 1003-1006 2007 conf/cikm/2007 CIKM http://doi.acm.org/10.1145/1321440.1321596 db/conf/cikm/cikm2007.html#XuBCY07