Do We Really Need Fully Unsupervised Cross-Lingual Embeddings?

Ivan Vulić, Goran Glavaš, Roi Reichart, Anna Korhonen


Abstract
Recent efforts in cross-lingual word embedding (CLWE) learning have predominantly focused on fully unsupervised approaches that project monolingual embeddings into a shared cross-lingual space without any cross-lingual signal. The lack of any supervision makes such approaches conceptually attractive. Yet, their only core difference from (weakly) supervised projection-based CLWE methods is in the way they obtain a seed dictionary used to initialize an iterative self-learning procedure. The fully unsupervised methods have arguably become more robust, and their primary use case is CLWE induction for pairs of resource-poor and distant languages. In this paper, we question the ability of even the most robust unsupervised CLWE approaches to induce meaningful CLWEs in these more challenging settings. A series of bilingual lexicon induction (BLI) experiments with 15 diverse languages (210 language pairs) show that fully unsupervised CLWE methods still fail for a large number of language pairs (e.g., they yield zero BLI performance for 87/210 pairs). Even when they succeed, they never surpass the performance of weakly supervised methods (seeded with 500-1,000 translation pairs) using the same self-learning procedure in any BLI setup, and the gaps are often substantial. These findings call for revisiting the main motivations behind fully unsupervised CLWE methods.
Anthology ID:
D19-1449
Volume:
Proceedings of the 2019 Conference on Empirical Methods in Natural Language Processing and the 9th International Joint Conference on Natural Language Processing (EMNLP-IJCNLP)
Month:
November
Year:
2019
Address:
Hong Kong, China
Editors:
Kentaro Inui, Jing Jiang, Vincent Ng, Xiaojun Wan
Venues:
EMNLP | IJCNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
4407–4418
Language:
URL:
https://aclanthology.org/D19-1449
DOI:
10.18653/v1/D19-1449
Bibkey:
Cite (ACL):
Ivan Vulić, Goran Glavaš, Roi Reichart, and Anna Korhonen. 2019. Do We Really Need Fully Unsupervised Cross-Lingual Embeddings?. In Proceedings of the 2019 Conference on Empirical Methods in Natural Language Processing and the 9th International Joint Conference on Natural Language Processing (EMNLP-IJCNLP), pages 4407–4418, Hong Kong, China. Association for Computational Linguistics.
Cite (Informal):
Do We Really Need Fully Unsupervised Cross-Lingual Embeddings? (Vulić et al., EMNLP-IJCNLP 2019)
Copy Citation:
PDF:
https://aclanthology.org/D19-1449.pdf
Attachment:
 D19-1449.Attachment.zip
Code
 ivulic/panlex-bli
Data
Panlex