Boosting Neural Machine Translation from Finnish to Northern Sámi with Rule-Based Backtranslation

Mikko Aulamo, Sami Virpioja, Yves Scherrer, Jörg Tiedemann

Abstract
We consider a low-resource translation task from Finnish into Northern Sámi. Collecting all available parallel data between the languages, we obtain around 30,000 sentence pairs. However, there exists a significantly larger monolingual Northern Sámi corpus, as well as a rule-based machine translation (RBMT) system between the languages. To make the best use of the monolingual data in a neural machine translation (NMT) system, we use the backtranslation approach to create synthetic parallel data from it using both NMT and RBMT systems. Evaluating the results on an in-domain test set and a small out-of-domain set, we find that the RBMT backtranslation outperforms NMT backtranslation clearly for the out-of-domain test set, but also slightly for the in-domain data, for which the NMT backtranslation model provided clearly better BLEU scores than the RBMT. In addition, combining both backtranslated data sets improves the RBMT approach only for the in-domain test set. This suggests that the RBMT system provides general-domain knowledge that cannot be found from the relative small parallel training data.
Anthology ID:
2021.nodalida-main.37
Volume:
Proceedings of the 23rd Nordic Conference on Computational Linguistics (NoDaLiDa)
Month:
May 31--2 June
Year:
2021
Address:
Reykjavik, Iceland (Online)
Editors:
Simon Dobnik, Lilja Øvrelid
Venue:
NoDaLiDa
SIG:
Publisher:
Linköping University Electronic Press, Sweden
Note:
Pages:
351–356
Language:
URL:
https://aclanthology.org/2021.nodalida-main.37
DOI:
Bibkey:
Cite (ACL):
Mikko Aulamo, Sami Virpioja, Yves Scherrer, and Jörg Tiedemann. 2021. Boosting Neural Machine Translation from Finnish to Northern Sámi with Rule-Based Backtranslation. In Proceedings of the 23rd Nordic Conference on Computational Linguistics (NoDaLiDa), pages 351–356, Reykjavik, Iceland (Online). Linköping University Electronic Press, Sweden.
Cite (Informal):
Boosting Neural Machine Translation from Finnish to Northern Sámi with Rule-Based Backtranslation (Aulamo et al., NoDaLiDa 2021)
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