Introduction

This repository contains the code used for soft contextual data augmentation proposed in ACL 2019 short paper, Soft Contextual Data Augmentation for Neural Machine Translation. Our code is based on fairseq. If you use this code or our results in your research, please cite the following paper:

@inproceedings{zhu2019soft,
  title={Soft Contextual Data Augmentation for Neural Machine Translation},
  author={Zhu, Jinhua and Gao, Fei and Wu, Lijun and Xia, Yingce and Qin, Tao and Zhou, Wengang and Cheng, Xueqi and Liu, Tie-Yan},
  booktitle={ACL 2019},
  year={2019}
}

Requirements and Installation

• A PyTorch installation

After PyTorch is installed, you can install fairseq with:

pip install -r requirements.txt
python setup.py build develop

Getting Started

Our method is divided into two steps:

1. Train two language models for source language and target language.
2. Train NMT models with pretrained language models.

Data prepeocessing

Following standard fairseq data preprocessing, you will get binarized translation datasets.

After that, you can copy datasets for language modeling in order to get the same vocabulary as NMT.

I shift a sentence twice in decoder input, so the shortest sentence length after bpe should be no less than 2.

src=en
tgt=ru
for l in $src $tgt; do
    srcdir=${src}2${tgt}
    tgtdir=lmof${l}
    mkdir -p $tgtdir
    cp $srcdir/dict.${l}.txt $tgtdir/dict.txt
    cp $srcdir/train.${src}-${tgt}.${l}.bin $tgtdir/train.bin
    cp $srcdir/train.${src}-${tgt}.${l}.idx $tgtdir/train.idx
    cp $srcdir/valid.${src}-${tgt}.${l}.bin $tgtdir/valid.bin
    cp $srcdir/valid.${src}-${tgt}.${l}.idx $tgtdir/valid.idx
done

Training of language model

I have modified this fairseq repo's dataloader, you'd better train language models with standard fairseq repo.

An example of our script:

python train.py $DATA  --task language_modeling --arch $ARCH \
  --optimizer adam --adam-betas '(0.9, 0.98)' --clip-norm 0.0 \
  --lr-scheduler inverse_sqrt --warmup-init-lr 1e-07 --warmup-updates 4000 \
  --lr 0.0005 --min-lr 1e-09 \
  --dropout 0.1 --weight-decay 0.0 --criterion label_smoothed_cross_entropy --label-smoothing 0.1 \
  --max-tokens 4096  --tokens-per-sample 4096  --save-dir $SAVE --update-freq 16

You can change the language model architecture according to your dataset size.

Training of NMT

The things I have added are as follows:

parser.add_argument('--load-lm', action='store_true',)
parser.add_argument('--load-srclm-file', type=str, default='checkpoint_src.pt')
parser.add_argument('--load-tgtlm-file', type=str, default='checkpoint_tgt.pt')
parser.add_argument('--load-nmt', action='store_true', )
parser.add_argument('--load-nmt-file', type=str, default='checkpoint_nmt.pt')
parser.add_argument('--tradeoff', type=float, default=0.1)

1. --load-lm is the flag to decide whether to load language model.
2. If you have specify --load-lm flag, you have place your two langage model checkpoints in $SAVE/load-srclm-file(load-tgtlm-file)
3. --tradeoff is the probability to add noise (i usually set it 0.1, 0.15, 0.2).
4. --load-nmt is the flag to decide whether to load a NMT model (only a nmt encoder and a decoder without language models) for warmup (I have not verified that this method will work, and i suggest you train your model from scratch).
5. If you have specify --load-nmt flag, you should also specify PATH for NMT model (--load-nmt-file).

An example of our script:

HOME=/blob/v-jinhzh/code/lm_fairseq
cd $HOME

export CUDA_VISIBLE_DEVICES=0,1,2,3
nvidia-smi

src={src}
tgt={tgt}
DATA_PATH=/blob/v-jinhzh/data/bt02/coldnmtdata01/{src}2{tgt}
python -c "import torch; print(torch.__version__)"

TRADEOFF={tradeoff}
SAVE_DIR=checkpoints/dataaug_{src}_{tgt}_{tradeoff}
mkdir -p ${{SAVE_DIR}}
chmod 777 ${{SAVE_DIR}}

cp /blob/v-jinhzh/code/fairseq_baseline/checkpoints/lmof{src}/checkpoint2.pt ${{SAVE_DIR}}/checkpoint_src.pt
cp /blob/v-jinhzh/code/fairseq_baseline/checkpoints/lmof{tgt}/checkpoint2.pt ${{SAVE_DIR}}/checkpoint_tgt.pt



echo SAVE_DIR ${{SAVE_DIR}}
echo TRADEOFF ${{TRADEOFF}}


python train.py ${{DATA_PATH}} --task lm_translation \
--arch transformer_vaswani_wmt_en_de_big --share-decoder-input-output-embed  \
--optimizer adam --adam-betas '(0.9, 0.98)' --clip-norm 0.0 \
--lr-scheduler inverse_sqrt --warmup-init-lr 1e-07 --warmup-updates 4000 \
--lr 0.0009 --min-lr 1e-09 \
--dropout 0.3 --weight-decay 0.0 --criterion label_smoothed_cross_entropy --label-smoothing 0.1 \
--max-tokens 2084 --update-freq 48 \
--save-dir ${{SAVE_DIR}} \
--tradeoff ${{TRADEOFF}} --load-lm --save-interval-updates 1000  --seed 200 \

I have modified the original transformer_vaswani_wmt_en_de_big arch config, and you have to specify language model arch according to your own language model if you have changed the above language model config.