Wordbased models (Zhang et al., 2016;Cai and Zhao, 2016;Cai et al., 2017;Yang et al., 2017) directly segment a character sequence into words and can easily achieve the benefits of word-level information.
these models cannot usually conduct exact inference because of strategies, such as beam-search decoding and constraints of maximum word length, which are necessary as the number of candidate segmentations increases exponentially with the sentence length.