Contrastive fine-tuning to improve generalization in deep NER

A novel algorithm of two-stage fine-tuning of a BERT-based language model for more effective named entity recognition is proposed. The first stage is based on training BERT as a Siamese network using a special contrastive loss function, and the second stage consists of fine-tuning the NER as a "traditional" sequence tagger. Inclusion of the contrastive first stage makes it possible to construct a high-level feature space at the output of BERT with more compact representations of different named entity classes. Experiments have shown that this fine-tuning scheme improves the generalization ability of named entity recognition models fine-tuned from various pre-trained BERT models. The source code is available under an Apache 2.0 license and hosted on GitHub https://github.com/ bond005/runne_contrastive_ner