Xuerui Wang Andrew McCallum Xing Wei Topical N-Grams: Phrase and Topic Discovery, with an Application to Information Retrieval. 697-702 2007 ICDM http://doi.ieeecomputersociety.org/10.1109/ICDM.2007.86 conf/icdm/2007 db/conf/icdm/icdm2007.html#WangMW07