CharBERT: Character-aware Pre-trained Language Model

Wentao Ma, Yiming Cui, Chenglei Si, Ting Liu, Shijin Wang, Guoping Hu


Abstract
Most pre-trained language models (PLMs) construct word representations at subword level with Byte-Pair Encoding (BPE) or its variations, by which OOV (out-of-vocab) words are almost avoidable. However, those methods split a word into subword units and make the representation incomplete and fragile.In this paper, we propose a character-aware pre-trained language model named CharBERT improving on the previous methods (such as BERT, RoBERTa) to tackle these problems. We first construct the contextual word embedding for each token from the sequential character representations, then fuse the representations of characters and the subword representations by a novel heterogeneous interaction module. We also propose a new pre-training task named NLM (Noisy LM) for unsupervised character representation learning. We evaluate our method on question answering, sequence labeling, and text classification tasks, both on the original datasets and adversarial misspelling test sets. The experimental results show that our method can significantly improve the performance and robustness of PLMs simultaneously.
Anthology ID:
2020.coling-main.4
Volume:
Proceedings of the 28th International Conference on Computational Linguistics
Month:
December
Year:
2020
Address:
Barcelona, Spain (Online)
Venue:
COLING
SIG:
Publisher:
International Committee on Computational Linguistics
Note:
Pages:
39–50
Language:
URL:
https://aclanthology.org/2020.coling-main.4
DOI:
10.18653/v1/2020.coling-main.4
Bibkey:
Cite (ACL):
Wentao Ma, Yiming Cui, Chenglei Si, Ting Liu, Shijin Wang, and Guoping Hu. 2020. CharBERT: Character-aware Pre-trained Language Model. In Proceedings of the 28th International Conference on Computational Linguistics, pages 39–50, Barcelona, Spain (Online). International Committee on Computational Linguistics.
Cite (Informal):
CharBERT: Character-aware Pre-trained Language Model (Ma et al., COLING 2020)
Copy Citation:
PDF:
https://aclanthology.org/2020.coling-main.4.pdf
Code
 wtma/CharBERT
Data
CoLACoNLL-2003GLUEMRPCQNLISQuAD