# BERT (Bidirectional Encoder Representations from Transformers)

The academic paper which describes BERT in detail and provides full results on a
number of tasks can be found here: https://arxiv.org/abs/1810.04805.

This repository contains TensorFlow 2.x implementation for BERT.

## Contents
  * [Contents](#contents)
  * [Pre-trained Models](#pre-trained-models)
    * [Restoring from Checkpoints](#restoring-from-checkpoints)
  * [Set Up](#set-up)
  * [Process Datasets](#process-datasets)
  * [Fine-tuning with BERT](#fine-tuning-with-bert)
    * [Cloud GPUs and TPUs](#cloud-gpus-and-tpus)
    * [Sentence and Sentence-pair Classification Tasks](#sentence-and-sentence-pair-classification-tasks)
    * [SQuAD 1.1](#squad-1.1)


## Pre-trained Models

We released both checkpoints and tf.hub modules as the pretrained models for
fine-tuning. They are TF 2.x compatible and are converted from the checkpoints
released in TF 1.x official BERT repository
[google-research/bert](https://github.com/google-research/bert)
in order to keep consistent with BERT paper.


### Access to Pretrained Checkpoints

Pretrained checkpoints can be found in the following links:

**Note: We have switched BERT implementation
to use Keras functional-style networks in [nlp/modeling](../modeling).
The new checkpoints are:**

*   **[`BERT-Large, Uncased (Whole Word Masking)`](https://storage.googleapis.com/cloud-tpu-checkpoints/bert/keras_bert/wwm_uncased_L-24_H-1024_A-16.tar.gz)**:
    24-layer, 1024-hidden, 16-heads, 340M parameters
*   **[`BERT-Large, Cased (Whole Word Masking)`](https://storage.googleapis.com/cloud-tpu-checkpoints/bert/keras_bert/wwm_cased_L-24_H-1024_A-16.tar.gz)**:
    24-layer, 1024-hidden, 16-heads, 340M parameters
*   **[`BERT-Base, Uncased`](https://storage.googleapis.com/cloud-tpu-checkpoints/bert/keras_bert/uncased_L-12_H-768_A-12.tar.gz)**:
    12-layer, 768-hidden, 12-heads, 110M parameters
*   **[`BERT-Large, Uncased`](https://storage.googleapis.com/cloud-tpu-checkpoints/bert/keras_bert/uncased_L-24_H-1024_A-16.tar.gz)**:
    24-layer, 1024-hidden, 16-heads, 340M parameters
*   **[`BERT-Base, Cased`](https://storage.googleapis.com/cloud-tpu-checkpoints/bert/keras_bert/cased_L-12_H-768_A-12.tar.gz)**:
    12-layer, 768-hidden, 12-heads , 110M parameters
*   **[`BERT-Large, Cased`](https://storage.googleapis.com/cloud-tpu-checkpoints/bert/keras_bert/cased_L-24_H-1024_A-16.tar.gz)**:
    24-layer, 1024-hidden, 16-heads, 340M parameters
*   **[`BERT-Base, Multilingual Cased`](https://storage.googleapis.com/cloud-tpu-checkpoints/bert/keras_bert/multi_cased_L-12_H-768_A-12.tar.gz)**:
    104 languages, 12-layer, 768-hidden, 12-heads, 110M parameters

We recommend to host checkpoints on Google Cloud storage buckets when you use
Cloud GPU/TPU.

### Restoring from Checkpoints

`tf.train.Checkpoint` is used to manage model checkpoints in TF 2. To restore
weights from provided pre-trained checkpoints, you can use the following code:

```python
init_checkpoint='the pretrained model checkpoint path.'
model=tf.keras.Model() # Bert pre-trained model as feature extractor.
checkpoint = tf.train.Checkpoint(model=model)
checkpoint.restore(init_checkpoint)
```

Checkpoints featuring native serialized Keras models
(i.e. model.load()/load_weights()) will be available soon.

### Access to Pretrained hub modules.

Pretrained tf.hub modules in TF 2.x SavedModel format can be found in the
following links:

*   **[`BERT-Large, Uncased (Whole Word Masking)`](https://tfhub.dev/tensorflow/bert_en_wwm_uncased_L-24_H-1024_A-16/1)**:
    24-layer, 1024-hidden, 16-heads, 340M parameters
*   **[`BERT-Large, Cased (Whole Word Masking)`](https://tfhub.dev/tensorflow/bert_en_wwm_cased_L-24_H-1024_A-16/1)**:
    24-layer, 1024-hidden, 16-heads, 340M parameters
*   **[`BERT-Base, Uncased`](https://tfhub.dev/tensorflow/bert_en_uncased_L-12_H-768_A-12/1)**:
    12-layer, 768-hidden, 12-heads, 110M parameters
*   **[`BERT-Large, Uncased`](https://tfhub.dev/tensorflow/bert_en_uncased_L-24_H-1024_A-16/1)**:
    24-layer, 1024-hidden, 16-heads, 340M parameters
*   **[`BERT-Base, Cased`](https://tfhub.dev/tensorflow/bert_en_cased_L-12_H-768_A-12/1)**:
    12-layer, 768-hidden, 12-heads , 110M parameters
*   **[`BERT-Large, Cased`](https://tfhub.dev/tensorflow/bert_en_cased_L-24_H-1024_A-16/1)**:
    24-layer, 1024-hidden, 16-heads, 340M parameters
*   **[`BERT-Base, Multilingual Cased`](https://tfhub.dev/tensorflow/bert_multi_cased_L-12_H-768_A-12/1)**:
    104 languages, 12-layer, 768-hidden, 12-heads, 110M parameters
*   **[`BERT-Base, Chinese`](https://tfhub.dev/tensorflow/bert_zh_L-12_H-768_A-12/1)**:
    Chinese Simplified and Traditional, 12-layer, 768-hidden, 12-heads,
    110M parameters

## Set Up

```shell
export PYTHONPATH="$PYTHONPATH:/path/to/models"
```

Install `tf-nightly` to get latest updates:

```shell
pip install tf-nightly-gpu
```

With TPU, GPU support is not necessary. First, you need to create a `tf-nightly`
TPU with [ctpu tool](https://github.com/tensorflow/tpu/tree/master/tools/ctpu):

```shell
ctpu up -name <instance name> --tf-version=”nightly”
```

Second, you need to install TF 2 `tf-nightly` on your VM:

```shell
pip install tf-nightly
```

## Process Datasets

### Pre-training

There is no change to generate pre-training data. Please use the script
[`../data/create_pretraining_data.py`](../data/create_pretraining_data.py)
which is essentially branched from [BERT research repo](https://github.com/google-research/bert)
to get processed pre-training data and it adapts to TF2 symbols and python3
compatibility.


### Fine-tuning

To prepare the fine-tuning data for final model training, use the
[`../data/create_finetuning_data.py`](../data/create_finetuning_data.py) script.
Resulting datasets in `tf_record` format and training meta data should be later
passed to training or evaluation scripts. The task-specific arguments are
described in following sections:

* GLUE

Users can download the
[GLUE data](https://gluebenchmark.com/tasks) by running
[this script](https://gist.github.com/W4ngatang/60c2bdb54d156a41194446737ce03e2e)
and unpack it to some directory `$GLUE_DIR`.
Also, users can download [Pretrained Checkpoint](#access-to-pretrained-checkpoints) and locate on some directory `$BERT_DIR` instead of using checkpoints on Google Cloud Storage.

```shell
export GLUE_DIR=~/glue
export BERT_DIR=gs://cloud-tpu-checkpoints/bert/keras_bert/uncased_L-24_H-1024_A-16

export TASK_NAME=MNLI
export OUTPUT_DIR=gs://some_bucket/datasets
python ../data/create_finetuning_data.py \
 --input_data_dir=${GLUE_DIR}/${TASK_NAME}/ \
 --vocab_file=${BERT_DIR}/vocab.txt \
 --train_data_output_path=${OUTPUT_DIR}/${TASK_NAME}_train.tf_record \
 --eval_data_output_path=${OUTPUT_DIR}/${TASK_NAME}_eval.tf_record \
 --meta_data_file_path=${OUTPUT_DIR}/${TASK_NAME}_meta_data \
 --fine_tuning_task_type=classification --max_seq_length=128 \
 --classification_task_name=${TASK_NAME}
```

* SQUAD

The [SQuAD website](https://rajpurkar.github.io/SQuAD-explorer/) contains
detailed information about the SQuAD datasets and evaluation.

The necessary files can be found here:

*   [train-v1.1.json](https://rajpurkar.github.io/SQuAD-explorer/dataset/train-v1.1.json)
*   [dev-v1.1.json](https://rajpurkar.github.io/SQuAD-explorer/dataset/dev-v1.1.json)
*   [evaluate-v1.1.py](https://github.com/allenai/bi-att-flow/blob/master/squad/evaluate-v1.1.py)
*   [train-v2.0.json](https://rajpurkar.github.io/SQuAD-explorer/dataset/train-v2.0.json)
*   [dev-v2.0.json](https://rajpurkar.github.io/SQuAD-explorer/dataset/dev-v2.0.json)
*   [evaluate-v2.0.py](https://worksheets.codalab.org/rest/bundles/0x6b567e1cf2e041ec80d7098f031c5c9e/contents/blob/)

```shell
export SQUAD_DIR=~/squad
export SQUAD_VERSION=v1.1
export BERT_DIR=gs://cloud-tpu-checkpoints/bert/keras_bert/uncased_L-24_H-1024_A-16
export OUTPUT_DIR=gs://some_bucket/datasets

python ../data/create_finetuning_data.py \
 --squad_data_file=${SQUAD_DIR}/train-${SQUAD_VERSION}.json \
 --vocab_file=${BERT_DIR}/vocab.txt \
 --train_data_output_path=${OUTPUT_DIR}/squad_${SQUAD_VERSION}_train.tf_record \
 --meta_data_file_path=${OUTPUT_DIR}/squad_${SQUAD_VERSION}_meta_data \
 --fine_tuning_task_type=squad --max_seq_length=384
```

Note: To create fine-tuning data with SQUAD 2.0, you need to add flag `--version_2_with_negative=True`.

## Fine-tuning with BERT

### Cloud GPUs and TPUs

* Cloud Storage

The unzipped pre-trained model files can also be found in the Google Cloud
Storage folder `gs://cloud-tpu-checkpoints/bert/keras_bert`. For example:

```shell
export BERT_DIR=gs://cloud-tpu-checkpoints/bert/keras_bert/uncased_L-24_H-1024_A-16
export MODEL_DIR=gs://some_bucket/my_output_dir
```

Currently, users are able to access to `tf-nightly` TPUs and the following TPU
script should run with `tf-nightly`.

* GPU -> TPU

Just add the following flags to `run_classifier.py` or `run_squad.py`:

```shell
  --distribution_strategy=tpu
  --tpu=grpc://${TPU_IP_ADDRESS}:8470
```

### Sentence and Sentence-pair Classification Tasks

This example code fine-tunes `BERT-Large` on the Microsoft Research Paraphrase
Corpus (MRPC) corpus, which only contains 3,600 examples and can fine-tune in a
few minutes on most GPUs.

We use the `BERT-Large` (uncased_L-24_H-1024_A-16) as an example throughout the
workflow.
For GPU memory of 16GB or smaller, you may try to use `BERT-Base`
(uncased_L-12_H-768_A-12).

```shell
export BERT_DIR=gs://cloud-tpu-checkpoints/bert/keras_bert/uncased_L-24_H-1024_A-16
export MODEL_DIR=gs://some_bucket/my_output_dir
export GLUE_DIR=gs://some_bucket/datasets
export TASK=MRPC

python run_classifier.py \
  --mode='train_and_eval' \
  --input_meta_data_path=${GLUE_DIR}/${TASK}_meta_data \
  --train_data_path=${GLUE_DIR}/${TASK}_train.tf_record \
  --eval_data_path=${GLUE_DIR}/${TASK}_eval.tf_record \
  --bert_config_file=${BERT_DIR}/bert_config.json \
  --init_checkpoint=${BERT_DIR}/bert_model.ckpt \
  --train_batch_size=4 \
  --eval_batch_size=4 \
  --steps_per_loop=1 \
  --learning_rate=2e-5 \
  --num_train_epochs=3 \
  --model_dir=${MODEL_DIR} \
  --distribution_strategy=mirrored
```

Alternatively, instead of specifying `init_checkpoint`, you can specify
`hub_module_url` to employ a pretraind BERT hub module, e.g.,
` --hub_module_url=https://tfhub.dev/tensorflow/bert_en_uncased_L-24_H-1024_A-16/1`.

After training a model, to get predictions from the classifier, you can set the
`--mode=predict` and offer the test set tfrecords to `--eval_data_path`.
Output will be created in file called test_results.tsv in the output folder.
Each line will contain output for each sample, columns are the class
probabilities.

```shell
python run_classifier.py \
  --mode='predict' \
  --input_meta_data_path=${GLUE_DIR}/${TASK}_meta_data \
  --eval_data_path=${GLUE_DIR}/${TASK}_eval.tf_record \
  --bert_config_file=${BERT_DIR}/bert_config.json \
  --eval_batch_size=4 \
  --model_dir=${MODEL_DIR} \
  --distribution_strategy=mirrored
```

To use TPU, you only need to switch distribution strategy type to `tpu` with TPU
information and use remote storage for model checkpoints.

```shell
export BERT_DIR=gs://cloud-tpu-checkpoints/bert/keras_bert/uncased_L-24_H-1024_A-16
export TPU_IP_ADDRESS='???'
export MODEL_DIR=gs://some_bucket/my_output_dir
export GLUE_DIR=gs://some_bucket/datasets
export TASK=MRPC

python run_classifier.py \
  --mode='train_and_eval' \
  --input_meta_data_path=${GLUE_DIR}/${TASK}_meta_data \
  --train_data_path=${GLUE_DIR}/${TASK}_train.tf_record \
  --eval_data_path=${GLUE_DIR}/${TASK}_eval.tf_record \
  --bert_config_file=${BERT_DIR}/bert_config.json \
  --init_checkpoint=${BERT_DIR}/bert_model.ckpt \
  --train_batch_size=32 \
  --eval_batch_size=32 \
  --steps_per_loop=1000 \
  --learning_rate=2e-5 \
  --num_train_epochs=3 \
  --model_dir=${MODEL_DIR} \
  --distribution_strategy=tpu \
  --tpu=grpc://${TPU_IP_ADDRESS}:8470
```

Note that, we specify `steps_per_loop=1000` for TPU, because running a loop of
training steps inside a `tf.function` can significantly increase TPU utilization
and callbacks will not be called inside the loop.

### SQuAD 1.1

The Stanford Question Answering Dataset (SQuAD) is a popular question answering
benchmark dataset. See more in [SQuAD website](https://rajpurkar.github.io/SQuAD-explorer/).

We use the `BERT-Large` (uncased_L-24_H-1024_A-16) as an example throughout the
workflow.
For GPU memory of 16GB or smaller, you may try to use `BERT-Base`
(uncased_L-12_H-768_A-12).

```shell
export BERT_DIR=gs://cloud-tpu-checkpoints/bert/keras_bert/uncased_L-24_H-1024_A-16
export SQUAD_DIR=gs://some_bucket/datasets
export MODEL_DIR=gs://some_bucket/my_output_dir
export SQUAD_VERSION=v1.1

python run_squad.py \
  --input_meta_data_path=${SQUAD_DIR}/squad_${SQUAD_VERSION}_meta_data \
  --train_data_path=${SQUAD_DIR}/squad_${SQUAD_VERSION}_train.tf_record \
  --predict_file=${SQUAD_DIR}/dev-v1.1.json \
  --vocab_file=${BERT_DIR}/vocab.txt \
  --bert_config_file=${BERT_DIR}/bert_config.json \
  --init_checkpoint=${BERT_DIR}/bert_model.ckpt \
  --train_batch_size=4 \
  --predict_batch_size=4 \
  --learning_rate=8e-5 \
  --num_train_epochs=2 \
  --model_dir=${MODEL_DIR} \
  --distribution_strategy=mirrored
```

Similarily, you can replace `init_checkpoint` FLAG with `hub_module_url` to
specify a hub module path.

`run_squad.py` writes the prediction for `--predict_file` by default. If you set
the `--model=predict` and offer the SQuAD test data, the scripts will generate
the prediction json file.

To use TPU, you need switch distribution strategy type to `tpu` with TPU
information.

```shell
export BERT_DIR=gs://cloud-tpu-checkpoints/bert/keras_bert/uncased_L-24_H-1024_A-16
export TPU_IP_ADDRESS='???'
export MODEL_DIR=gs://some_bucket/my_output_dir
export SQUAD_DIR=gs://some_bucket/datasets
export SQUAD_VERSION=v1.1

python run_squad.py \
  --input_meta_data_path=${SQUAD_DIR}/squad_${SQUAD_VERSION}_meta_data \
  --train_data_path=${SQUAD_DIR}/squad_${SQUAD_VERSION}_train.tf_record \
  --predict_file=${SQUAD_DIR}/dev-v1.1.json \
  --vocab_file=${BERT_DIR}/vocab.txt \
  --bert_config_file=${BERT_DIR}/bert_config.json \
  --init_checkpoint=${BERT_DIR}/bert_model.ckpt \
  --train_batch_size=32 \
  --learning_rate=8e-5 \
  --num_train_epochs=2 \
  --model_dir=${MODEL_DIR} \
  --distribution_strategy=tpu \
  --tpu=grpc://${TPU_IP_ADDRESS}:8470
```

The dev set predictions will be saved into a file called predictions.json in the
model_dir:

```shell
python $SQUAD_DIR/evaluate-v1.1.py $SQUAD_DIR/dev-v1.1.json ./squad/predictions.json
```


