BlonDe: An Automatic Evaluation Metric for Document-level Machine Translation
Written for the Research library (claude-opus-5-5) from the paper text. Original — aclanthology.org/2022.naacl-main.111.pdf
Summary
Sentence-level metrics such as BLEU cannot tell whether a translation system improves document-level coherence, and they cannot point to the discourse problems behind context-unaware output. The authors build BWB, a large Chinese–English corpus of web novels paired with professional English translations. Professional translators annotated MT errors in its test set and found that most translations contain document-level mistakes, chiefly inconsistency, ellipsis, and ambiguity. From these findings they design BlonDe, a reference-based metric. It sorts discourse-relevant spans into categories (named entities, tense, pronoun gender, discourse markers) and n-grams, matches system and reference spans through a similarity-based bijection, and reports precision, recall, and F1. Human annotations can be added as extra categories. Compared with 11 existing metrics, BlonDe better separates context-aware from context-agnostic systems and correlates less with sentence-level metrics, which suggests it captures additional quality signals. It also achieves the highest Pearson correlation with human judgments. This makes it a practical, interpretable alternative to costly hand-built discourse test suites.
Key points
- BWB corpus: about 196K documents (chapters) and 9.58M sentences, which the authors describe as the largest Chinese–English document-level dataset. The training set was aligned with Bleualign, with 93.1% alignment accuracy on a manual check. Dev and test sets (79/80 documents) were manually corrected.
- Error analysis: 71.9% of MT outputs contain document-level errors. The most frequent categories are inconsistency (64.4%), ellipsis (20.3%), and ambiguity (7.3%), which together make up 86.73% of mistakes.
- Human evaluation: professional translators and revisers rated fluency and adequacy at both sentence and document level, and differences were checked with the Williams significance test. BlonDe correlates best with human ratings at both levels, but its advantage over all other metrics is statistically significant only at the document level.
- Variants: BlonD-D and BlonD+ extend the base metric. Recall-oriented variants track human judgments more closely, while precision-oriented ones are more selective. This trade-off is why F1 is the default.
- Availability: the code is released at github.com/EleanorJiang/BlonDe. The authors also plan to release the annotated BWB test set and a crawling script for the training data.
Cited by
- Large Language Models Effectively Leverage Document-level Context for Literary Translation, but Critical Errors Persist
- Embarrassingly Easy Document-Level MT Metrics: How to Convert Any Pretrained Metric into a Document-Level Metric
Cite
@inproceedings{jiang2022blonde,
title = {{BlonDe: An Automatic Evaluation Metric for Document-level Machine Translation}},
author = {Jiang, Yuchen and Liu, Tianyu and Ma, Shuming and Zhang, Dongdong and Yang, Jian and Huang, Haoyang and Sennrich, Rico and Cotterell, Ryan and Sachan, Mrinmaya and Zhou, Ming},
booktitle = {Proceedings of the 2022 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies},
year = {2022},
doi = {10.18653/v1/2022.naacl-main.111},
url = {https://doi.org/10.18653/v1/2022.naacl-main.111}
}References
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