Hypergraph network model for nested entity mention recognition

We propose a hypergraph network (HGN) model to recognize the nested entity mentions in texts. This model can learn the representations for the sequence structures of natural languages and the representations for the hypergraph structures of nested entity mentions. Mainstream methods recognize an entity mention by separately tagging the words or the gaps between words, which may complicate the problem and not be favorable for capturing the overall features of the mention. To solve these issues, the HGN model treats each entity mention as a whole and tags it with one label. We represent each sentence as a hypergraph, in which nodes represent words and hyperedges represent entity mentions. Thus, entity mention recognition (EMR) is transformed into a task of classifying the hyperedges. The HGN model firstly uses encoders to extract the features and learn a hypergraph representation, and then recognizes entity mentions by tagging every hyperedge. The experiments on three standard datasets demonstrate our model outperforms the previous models for nested EMR. We openly release the source code at https://github.com/nlplab-ie/HGN.