“…There are several categories of related approaches, including those that learn a single embedding for unseen words (Søgaard and Johannsen, 2012;Chen and Manning, 2014;Collobert et al, 2011), those that use character-level information (Luong et al, 2013;Botha and Blunsom, 2014;, those using morphological and n-gram information (Candito and Crabbé, 2009;Habash, 2009;Marton et al, 2010;Seddah et al, 2010;Attia et al, 2010;Bansal and Klein, 2011;Keller and Lapata, 2003), and hybrid approaches Jean et al, 2015;Luong et al, 2015;Chitnis and DeNero, 2015). The representation for the unknown token is either learned specifically or computed from a selection of rare words, for example by averaging their embedding vectors.…”