Unsupervised machine translation - i.e., not assuming any cross-lingual supervision signal, whether a dictionary, translations, or comparable corpora - seems impossible, but nevertheless, Lample et al. (2017) recently proposed a fully unsupervised machine translation (MT) model. The model relies heavily on an adversarial, unsupervised cross-lingual word embedding technique for bilingual dictionary induction (Conneau et al., 2017), which we examine here. Our results identify the limitations of current unsupervised MT: unsupervised bilingual dictionary induction performs much worse on morphologically rich languages that are not dependent marking, when monolingual corpora from different domains or different embedding algorithms are used. We show that a simple trick, exploiting a weak supervision signal from identical words, enables more robust induction and establish a near-perfect correlation between unsupervised bilingual dictionary induction performance and a previously unexplored graph similarity metric.
On the Limitations of Unsupervised Bilingual Dictionary Induction
Anders Søgaard,Sebastian Ruder,Ivan Vulic
Published 2018 in Annual Meeting of the Association for Computational Linguistics
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- Publication year
2018
- Venue
Annual Meeting of the Association for Computational Linguistics
- Publication date
2018-05-09
- Fields of study
Mathematics, Linguistics, Computer Science
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