Cross-Attention Transfer for Machine Translation

This repo hosts the code to accompany the camera-ready version of "Cross-Attention is All You Need: Adapting Pretrained Transformers for Machine Translation" in EMNLP 2021.

Setup

We provide our scripts and modifications to Fairseq. In this section, we describe how to go about running the code and, for instance, reproduce Table 2 in the paper.

Data

To view the data as we prepared and used it, switch to the main branch. But we recommend cloning code from this branch to avoid downloading a large amount of data at once. You can always obtain any data as necessary from the main branch.

Installations

We worked in a conda environment with Python 3.8.

• First install the requirements.

    pip install requirements.txt

• Then install Fairseq. To have the option to modify the package, install it in editable mode.

    cd fairseq-modified
    pip install -e .

• Finally, set the following environment variable.

    export FAIRSEQ=$PWD
    cd ..

Experiments

For the purpose of this walk-through, we assume we want to train a De–En model, using the following data:

De-En
├── iwslt13.test.de
├── iwslt13.test.en
├── iwslt13.test.tok.de
├── iwslt13.test.tok.en
├── iwslt15.tune.de
├── iwslt15.tune.en
├── iwslt15.tune.tok.de
├── iwslt15.tune.tok.en
├── iwslt16.train.de
├── iwslt16.train.en
├── iwslt16.train.tok.de
└── iwslt16.train.tok.en

by transferring from a Fr–En parent model, the experiment files of which is stored under FrEn/checkpoints.

• Start by making an experiment folder and preprocessing the data.

    mkdir test_exp
    ./xattn-transfer-for-mt/scripts/data_preprocessing/prepare_bi.sh \
        de en test_exp/ \
        De-En/iwslt16.train.tok De-En/iwslt15.tune.tok De-En/iwslt13.test.tok \
        8000

  Please note that prepare_bi.sh is written for the most general case, where you are learning vocabulary for both the source and target sides. When necessary modify it, and reuse whatever vocabulary you want. In this case, e.g., since we are transferring from Fr–En to De–En, we will reuse the target side vocabulary from the parent. So 8000 refers to the source vocabulary size, and we need to copy parent target vocabulary instead of learning one in the script.

    cp ./FrEn/data/tgt.sentencepiece.bpe.model $DATA
    cp ./FrEn/data/tgt.sentencepiece.bpe.vocab $DATA

• Now you can run an experiment. Here we want to just update the source embeddings and the cross-attention. So we run the corresponding script. Script names are self-explanatory. Set the correct path to the desired parent model checkpoint in the script, and:

    bash ./xattn-transfer-for-mt/scripts/training/reinit-src-embeddings-and-finetune-parent-model-on-translation_src+xattn.sh \
        test_exp/ de en

• Finally, after training, evaluate your model. Set the correct path to the detokenizer that you use in the script, and:

    bash ./xattn-transfer-for-mt/scripts/evaluation/decode_and_score_valid_and_test.sh \
        test_exp/ de en \
        $PWD/De-En/iwslt15.tune.en $PWD/De-En/iwslt13.test.en

Issues

Please contact us and report any problems you might face through the issues tab of the repo. Thanks in advance for helping us improve the repo!

Credits

The main body of code is built upon Fairseq. We found it very easy to navigate and modify. Kudos to the developers!
The data preprocessing scripts are adopted from FLORES scripts.
To have mBART fit on the GPUs that we worked with memory-wise, we used the trimming solution provided here.

Citation

@inproceedings{gheini-cross-attention,
  title = "Cross-Attention is All You Need: {A}dapting Pretrained {T}ransformers for Machine Translation",
  author = "Gheini, Mozhdeh and Ren, Xiang and May, Jonathan",
  booktitle = "Proceedings of the 2021 Conference on Empirical Methods in Natural Language Processing (EMNLP)",
  month = nov,
  year = "2021"
}