Chinese Word Segmentation via BiLSTM+Semi-CRF with Relay Node

Semi-Markov conditional random fields (Semi-CRFs) have been successfully utilized in many segmentation problems, including Chinese word segmentation (CWS). The advantage of Semi-CRF lies in its inherent ability to exploit properties of segments instead of individual elements of sequences. Despite its theoretical advantage, Semi-CRF is still not the best choice for CWS because its computation complexity is quadratic to the sentence's length. In this paper, we propose a simple yet effective framework to help Semi-CRF achieve comparable performance with CRF-based models under similar computation complexity. Specifically, we first adopt a bi-directional long short-term memory (BiLSTM) on character level to model the context information, and then use simple but effective fusion layer to represent the segment information. Besides, to model arbitrarily long segments within linear time complexity, we also propose a new model named Semi-CRFRelay. The direct modeling of segments makes the combination with word features easy and the CWS performance can be enhanced merely by adding publicly available pre-trained word embeddings. Experiments on four popular CWS datasets show the effectiveness of our proposed methods. The source codes and pre-trained embeddings of this paper are available on https://github.com/fastnlp/fastNLP/.