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PEGASUS library

Pre-training with Extracted Gap-sentences for Abstractive SUmmarization Sequence-to-sequence models, or PEGASUS, uses self-supervised objective Gap Sentences Generation (GSG) to train a transformer encoder-decoder model. The paper can be found on arXiv.

Setup

create an instance on google cloud with GPU (optional)

Please create a project first and create an instance

gcloud compute instances create \
  ${VM_NAME} \
  --zone=${ZONE} \
  --machine-type=n1-highmem-8 \
  --accelerator type=nvidia-tesla-v100,count=1 \
  --boot-disk-size=500GB \
  --image-project=ml-images \
  --image-family=tf-1-15 \
  --maintenance-policy TERMINATE --restart-on-failure

install library and dependencies

Clone library on github and install requirements.

git clone https://github.com/google-research/pegasus
cd pegasus
export PYTHONPATH=.
pip3 install -r requirements.txt

Download vocab and model checkpoint

sudo apt install gsutil
mkdir ckpt
gsutil cp gs://pegasus_ckpt/* ckpt/

Finetuning on downstream datasets

on existing dataset

Finetune on an existing dataset aeslc.

python3 pegasus/bin/train.py --params=aeslc_transformer \
--param_overrides=vocab_filename=ckpt/c4.unigram.newline.10pct.96000.model \
--train_init_checkpoint=ckpt/model.ckpt-1500000 \
--model_dir=aeslc

Evaluate on the finetuned dataset.

python3 pegasus/bin/evaluate.py --params=aeslc_transformer \
--param_overrides=vocab_filename=ckpt/c4.unigram.newline.10pct.96000.model,batch_size=1,beam_size=5,beam_alpha=0.6 \
--model_dir=aeslc

Note that the above example is using a single GPU so the batch_size is much smaller than the results reported in the paper.

add new finetuning dataset

Two types of dataset format are supported: TensorFlow Datasets (TFDS) or TFRecords.

This tutorial shows how to add a new dataset in TFDS. (The fine-tuning dataset is expected to be supervised, please provide supervised_keys in dataset info).

Tfrecords format requires each record to be a tf example of {"inputs":tf.string, "targets":tf.string}.

For example, if you registered a TFDS dataset called new_tfds_dataset for training and evaluation, and have some files in tfrecord format called new_dataset_files.tfrecord* for test, they can be registered in /pegasus/params/public_params.py.

@registry.register("new_params")
def my_param(param_overrides):
  return public_params.transformer_params(
      {
          "train_pattern": "tfds:new_tfds_dataset,train",
          "dev_pattern": "tfds:new_tfds_dataset,validation",
          "test_pattern": "tfrecord:new_dataset_files.tfrecord*",
          "max_input_len": 512,
          "max_output_len": 128,
          "train_steps": 10000,
          "learning_rate": 0.0001,
          "batch_size": 8,
      }, param_overrides)

Evaluation metrics.

Evaluation results can be found in mode_dir. Summarization metrics are automatically calculated for each evaluation point.

  • ROUGE is the main metric for summarization quality.

  • BLEU is an alternative quality metric for language generation.

  • Extractive Fragments Coverage & Density are metrics that measures the abstractiveness of the summary.

  • Repetition Rates measures generation repetition failure modes.

  • Length statistics measures the length distribution of decodes comparing to gold summary.

Several types of output files can be found in model_dir

  • text_metrics-*.txt: above metrics in text format. Each row contains metric name, 95% lower bound value, mean value, 95% upper bound value.
  • inputs-.txt, targets-.txt, predictions-*.txt: raw text files of model inputs/outputs.

Pre-training

Pretraining (on C4 or any other corpus) requires a customly built tensorflow that includes ops for on-the-fly parsing that processes raw text document into model inputs and targets ids. Please refer to pegasus/ops/pretrain_parsing_ops.cc and pegasus/data/parsers.py for details.