Lei Guo Enhua Tan Songqing Chen Xiaodong Zhang Yihong Eric Zhao Analyzing patterns of user content generation in online social networks. 369-378 2009 KDD http://doi.acm.org/10.1145/1557019.1557064 conf/kdd/2009 db/conf/kdd/kdd2009.html#GuoTCZZ09