Most of state-of-the-art models utilize the framework of word LSTM-CRF with character LSTM or CNN features (correspond to "CLSTM+WLSTM+CRF" and "CCNN+WLSTM+CRF" of our models) (Lample et al., 2016;<cite> Ma and Hovy, 2016</cite>; Yang et al., 2017; Peters et al., 2017) .