Char2Subword: Extending the Subword Embedding Space Using Robust Character Compositionality
Gustavo Aguilar, Bryan McCann, Tong Niu, Nazneen Rajani, Nitish Shirish Keskar, Thamar Solorio
Abstract
Byte-pair encoding (BPE) is a ubiquitous algorithm in the subword tokenization process of language models as it provides multiple benefits. However, this process is solely based on pre-training data statistics, making it hard for the tokenizer to handle infrequent spellings. On the other hand, though robust to misspellings, pure character-level models often lead to unreasonably long sequences and make it harder for the model to learn meaningful words. To alleviate these challenges, we propose a character-based subword module (char2subword) that learns the subword embedding table in pre-trained models like BERT. Our char2subword module builds representations from characters out of the subword vocabulary, and it can be used as a drop-in replacement of the subword embedding table. The module is robust to character-level alterations such as misspellings, word inflection, casing, and punctuation. We integrate it further with BERT through pre-training while keeping BERT transformer parameters fixed–and thus, providing a practical method. Finally, we show that incorporating our module to mBERT significantly improves the performance on the social media linguistic code-switching evaluation (LinCE) benchmark.- Anthology ID:
- 2021.findings-emnlp.141
- Volume:
- Findings of the Association for Computational Linguistics: EMNLP 2021
- Month:
- November
- Year:
- 2021
- Address:
- Punta Cana, Dominican Republic
- Venue:
- Findings
- SIG:
- SIGDAT
- Publisher:
- Association for Computational Linguistics
- Note:
- Pages:
- 1640–1651
- Language:
- URL:
- https://aclanthology.org/2021.findings-emnlp.141
- DOI:
- 10.18653/v1/2021.findings-emnlp.141
- Cite (ACL):
- Gustavo Aguilar, Bryan McCann, Tong Niu, Nazneen Rajani, Nitish Shirish Keskar, and Thamar Solorio. 2021. Char2Subword: Extending the Subword Embedding Space Using Robust Character Compositionality. In Findings of the Association for Computational Linguistics: EMNLP 2021, pages 1640–1651, Punta Cana, Dominican Republic. Association for Computational Linguistics.
- Cite (Informal):
- Char2Subword: Extending the Subword Embedding Space Using Robust Character Compositionality (Aguilar et al., Findings 2021)
- PDF:
- https://preview.aclanthology.org/ingestion-script-update/2021.findings-emnlp.141.pdf
- Data
- LinCE