Yunzhang Zhu Gang Wang Junli Yang Dakan Wang Jun Yan Zheng Chen Revenue optimization with relevance constraint in sponsored search. 55-60 2009 KDD Workshop on Data Mining and Audience Intelligence for Advertising http://doi.acm.org/10.1145/1592748.1592756 conf/kdd/2009adkdd db/conf/kdd/adkdd2009.html#ZhuWYWYC09