Log-linear Combinations of Monolingual and Bilingual Neural Machine Translation Models for Automatic Post-Editing
Summary
The paper tackles automatic post-editing (APE): repairing the output of an unseen machine translation system (English→German, IT domain) in the WMT 2016 shared task. The AMU team applied attention-based neural encoder-decoder models to this problem. The official post-editing data was far too small, so they created millions of synthetic triplets. They filtered German Common Crawl text by cross-entropy and passed it through German→English→German round-trip translation with phrase-based systems. They then kept the triplets whose TER statistics most closely resembled the real APE data. They trained two kinds of NMT models: monolingual ones (MT output → post-edit) and bilingual ones (English source → post-edit). Their ensembles were merged in a tuned log-linear model with a simple Post-Editing Penalty that discourages words absent from the input. This setup captures both the MT output and the source sentence and keeps corrections conservative. The final system ranked first in the shared task by a wide margin. It showed early on that neural models, given enough synthetic data, can beat phrase-based APE approaches.
Key points
- Data: 12,000 official training triplets and 1,000 development triplets, plus about 10 million artificial triplets from round-trip translation. These were filtered by TER similarity into round-trip.n10 (4,335,715 triplets) and round-trip.n1 (531,839 triplets).
- Preprocessing used the Moses tokenizer and truecaser and BPE subword units with 40,000 units per language. German MT output and post-edits shared one vocabulary.
- Models: four mt→pe and four src→pe checkpoints were combined log-linearly in AmuNMT. The Post-Editing Penalty adds a −1 cost for each output word not seen in the input.
- On the development set, the full system improved over the raw MT baseline by −3.7% TER and +6.0% BLEU. It also gained −1.8% TER and +2.1% BLEU over the monolingual-only ensemble.
- On the test set, the system scored 21.52 TER and 67.65 BLEU, against 24.76 TER and 62.11 BLEU for uncorrected MT (−3.2% TER, +5.5% BLEU). The best other team, FBK, reached 23.92 TER.
Cited by
- Findings of the 2021 Conference on Machine Translation (WMT21)
- Findings of the 2016 Conference on Machine Translation
- Findings of the 2017 Conference on Machine Translation (WMT17)
- Findings of the WMT 2019 Shared Task on Automatic Post-Editing
- APE at Scale and Its Implications on MT Evaluation Biases
Cite
@inproceedings{junczysdowmunt2016log,
title = {{Log-linear Combinations of Monolingual and Bilingual Neural Machine Translation Models for Automatic Post-Editing}},
author = {Junczys-Dowmunt, Marcin and Grundkiewicz, Roman},
booktitle = {Proceedings of the First Conference on Machine Translation: Volume 2, Shared Task Papers},
year = {2016},
doi = {10.18653/v1/w16-2378},
url = {https://doi.org/10.18653/v1/w16-2378}
}References
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