Tokenization Impacts Multilingual Language Modeling: Assessing Vocabulary Allocation and Overlap Across Languages

Tomasz Limisiewicz, Jiří Balhar, David Mareček


Abstract
Multilingual language models have recently gained attention as a promising solution for representing multiple languages in a single model. In this paper, we propose new criteria to evaluate the quality of lexical representation and vocabulary overlap observed in sub-word tokenizers.Our findings show that the overlap of vocabulary across languages can be actually detrimental to certain downstream tasks (POS, dependency tree labeling). In contrast, NER and sentence-level tasks (cross-lingual retrieval, NLI) benefit from sharing vocabulary. We also observe that the coverage of the language-specific tokens in the multilingual vocabulary significantly impacts the word-level tasks. Our study offers a deeper understanding of the role of tokenizers in multilingual language models and guidelines for future model developers to choose the most suitable tokenizer for their specific application before undertaking costly model pre-training.
Anthology ID:
2023.findings-acl.350
Volume:
Findings of the Association for Computational Linguistics: ACL 2023
Month:
July
Year:
2023
Address:
Toronto, Canada
Editors:
Anna Rogers, Jordan Boyd-Graber, Naoaki Okazaki
Venue:
Findings
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
5661–5681
Language:
URL:
https://aclanthology.org/2023.findings-acl.350
DOI:
10.18653/v1/2023.findings-acl.350
Bibkey:
Cite (ACL):
Tomasz Limisiewicz, Jiří Balhar, and David Mareček. 2023. Tokenization Impacts Multilingual Language Modeling: Assessing Vocabulary Allocation and Overlap Across Languages. In Findings of the Association for Computational Linguistics: ACL 2023, pages 5661–5681, Toronto, Canada. Association for Computational Linguistics.
Cite (Informal):
Tokenization Impacts Multilingual Language Modeling: Assessing Vocabulary Allocation and Overlap Across Languages (Limisiewicz et al., Findings 2023)
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PDF:
https://aclanthology.org/2023.findings-acl.350.pdf
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 https://aclanthology.org/2023.findings-acl.350.mp4