Existing sentence regression methods usually model sentence importance and sentence redundancy in two separate processes, namely sentence ranking and sentence selection.
in the sentence ranking process, they evaluate the importance f (s) of each sentence s with a ranking model (Osborne, 2002;Conroy et al., 2004;Galley, 2006; through either directly measuring the salience of sentences  or firstly ranking words (or bi-grams) and then combining these scores to rank sentences (Lin and Hovy, 2000;Yih et al., 2007;Gillick and Favre, 2009;Li et al., 2013).