It can involve morphological information (Luong et al., 2013) derived from the character level (Santos and Zadrozny, 2014; Labeau et al., 2015), and often make use of external resources: semantic lexicon (Faruqui et al., 2015), and pre-trained embeddings from larger corpora (Komiya and Shinnou, 2018).
to our knowledge, no work has attempted to apply similar solutions to the problem of sparse data in temporal corpora, even thought this situation has been faced by many authors, often in the case of short time steps for social media data (Stewart et al., 2017;Bamler and Mandt, 2017;Kulkarni et al., 2015).