Following (Serban et al., 2016;Elsahar et al., 2018), we adopt some word-overlap based metrics (WBMs) for natural language generation including BLEU-4 (Papineni et al., 2002), ROUGE L (Lin, 2004) and METEOR (Denkowski and Lavie, 2014).
such metrics still suffer from some limitations (Novikova et al., 2017).