---
title: "A Simple and Effective Unified Encoder for Document-Level"
description: "This dual-encoder design limits how context and the current sentence interact, and it does not match… 30 references, cited by 63 papers here."
authors: ["Shuming Ma", "Dongdong Zhang", "Ming Zhou"]
year: 2020
venue: "Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics"
source: "https://aclanthology.org/2020.acl-main.321/"
doi: "10.18653/v1/2020.acl-main.321"
licence: "CC BY 4.0 (ACL Anthology)"
licence_url: "https://creativecommons.org/licenses/by/4.0/"
summary_licence: "Elamur Cosmic License"
canonical: "https://research.elamur.ai/free/en/papers/ma-2020-simple-effective-unified-encoder-document/"
---
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# A Simple and Effective Unified Encoder for Document-Level Machine Translation

**Authors:** [Shuming Ma](https://md.research.elamur.ai/free/en/authors/shuming-ma/), [Dongdong Zhang](https://md.research.elamur.ai/free/en/authors/dongdong-zhang/) and [Ming Zhou](https://md.research.elamur.ai/free/en/authors/ming-zhou/) · **Year:** 2020 · **Venue:** [Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics](https://md.research.elamur.ai/free/en/venues/acl/) ([ACL 2020](https://md.research.elamur.ai/free/en/venues/acl/2020/)) · **Publisher:** [Association for Computational Linguistics](https://md.research.elamur.ai/free/en/publishers/association-for-computational-linguistics/) · **Licence:** [CC BY 4.0 (ACL Anthology)](https://creativecommons.org/licenses/by/4.0/)

**Links:** [Publisher's page](https://aclanthology.org/2020.acl-main.321/) · [PDF](https://aclanthology.org/2020.acl-main.321.pdf) · [DOI 10.18653/v1/2020.acl-main.321](https://doi.org/10.18653/v1/2020.acl-main.321) · [OpenAlex](https://openalex.org/W3034351728)

**Citations:** 73 citations (OpenAlex, 2026-10-14) · [63](https://md.research.elamur.ai/free/en/papers/ma-2020-simple-effective-unified-encoder-document/cited-by/) in our library, of the 141,840 papers whose bibliographies we read

## Summary
Document-level machine translation systems usually encode the surrounding sentences with a separate context encoder. This dual-encoder design limits how context and the current sentence interact, and it does not match single-encoder pre-trained models such as BERT. The authors propose Flat-Transformer, which feeds the context (one preceding and one following sentence) and the current source sentence into one shared encoder as a single sequence. Segment embeddings tell the model which tokens are context and which are source. The lower encoder block attends over the whole sequence, while the upper blocks process only the source positions. This keeps attention focused on the sentence being translated and adds no parameters beyond a standard Transformer. Tested on English-German TED, News and Europarl, the model outperforms earlier uni-encoder baselines. When initialized from BERT, it surpasses dual-encoder systems such as HAN, SAN and QCN on nearly every metric. The work shows that a simple flat architecture can take advantage of pre-training for context-aware translation.

## Key points
- **Data:** three English-German benchmarks (TED, News, Europarl), using the preprocessed versions from Maruf et al. (2019). Text was tokenized with Moses and split into BPE subwords with 30K merges. Evaluation uses BLEU and METEOR.
- **Architecture:** 1 bottom block runs over the full context-plus-source sequence, and 5 top blocks run over source positions only. The parameter count equals that of a standard Transformer.
- **Base Flat-Transformer results:**
  - BLEU: 24.87 / 23.55 / 30.09 (TED / News / Europarl).
  - METEOR: 47.05 / 43.97 / 48.56.
  - Both beat the uni-encoder RNNSearch and Transformer baselines.
- **With BERT initialization:**
  - BLEU rises to 26.61 / 24.52 / 31.99, and METEOR to 48.53 / 45.40 / 49.76.
  - This beats all dual-encoder baselines except News BLEU, where HAN scores 25.03.
  - In contrast, adding BERT to the dual-encoder Transformer lowered its BLEU on TED and News.
- **Ablation on TED:**
  - Segment embeddings contribute +0.51 BLEU and +0.85 METEOR.
  - The unified flat structure contributes a further +1.08 BLEU and +2.03 METEOR.

*Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.*

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## Cite

Cite as: Shuming Ma, Dongdong Zhang and Ming Zhou. 2020. A Simple and Effective Unified Encoder for Document-Level Machine Translation. Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics.

The paper itself, not this page. BibTeX from the library's record of the work.

```bibtex
@inproceedings{ma2020simple,
  title = {{A Simple and Effective Unified Encoder for Document-Level Machine Translation}},
  author = {Shuming Ma, Dongdong Zhang and Ming Zhou},
  booktitle = {Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics},
  year = {2020},
  doi = {10.18653/v1/2020.acl-main.321},
  url = {https://doi.org/10.18653/v1/2020.acl-main.321}
}
```

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## References

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*Updated 24 October 2026*