There have been many studies on sentiment classification and opinion summarization Lee, 2004, 2005;Gamon et al., 2005;Popescu and Etzioni, 2005;Liu et al., 2005;Zhuang et al., 2006;Kim and Hovy, 2006).
aspect rating as an interesting topic has also been widely studied (Titov and McDonald, 2008a;Snyder and Barzilay, 2007;Goldberg and Zhu, 2006).