Add BertEncoder to keras_nlp.

PiperOrigin-RevId: 332122408

official/nlp/keras_nlp/encoders/__init__.py

+# Copyright 2020 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Keras-NLP layers package definition."""
+from official.nlp.keras_nlp.encoders.bert_encoder import BertEncoder

official/nlp/keras_nlp/encoders/bert_encoder.py

+# Copyright 2020 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Bert encoder network."""
+# pylint: disable=g-classes-have-attributes
+
+import tensorflow as tf
+
+from official.nlp.keras_nlp import layers
+
+
+@tf.keras.utils.register_keras_serializable(package='keras_nlp')
+class BertEncoder(tf.keras.Model):
+  """Bi-directional Transformer-based encoder network.
+
+  This network implements a bi-directional Transformer-based encoder as
+  described in "BERT: Pre-training of Deep Bidirectional Transformers for
+  Language Understanding" (https://arxiv.org/abs/1810.04805). It includes the
+  embedding lookups and transformer layers, but not the masked language model
+  or classification task networks.
+
+  The default values for this object are taken from the BERT-Base implementation
+  in "BERT: Pre-training of Deep Bidirectional Transformers for Language
+  Understanding".
+
+  *Note* that the network is constructed by
+  [Keras Functional API](https://keras.io/guides/functional_api/).
+
+  Arguments:
+    vocab_size: The size of the token vocabulary.
+    hidden_size: The size of the transformer hidden layers.
+    num_layers: The number of transformer layers.
+    num_attention_heads: The number of attention heads for each transformer. The
+      hidden size must be divisible by the number of attention heads.
+    max_sequence_length: The maximum sequence length that this encoder can
+      consume. If None, max_sequence_length uses the value from sequence length.
+      This determines the variable shape for positional embeddings.
+    type_vocab_size: The number of types that the 'type_ids' input can take.
+    inner_dim: The output dimension of the first Dense layer in a two-layer
+        feedforward network for each transformer.
+    inner_activation: The activation for the first Dense layer in a two-layer
+        feedforward network for each transformer.
+    output_dropout: Dropout probability for the post-attention and output
+        dropout.
+    attention_dropout: The dropout rate to use for the attention layers
+      within the transformer layers.
+    initializer: The initialzer to use for all weights in this encoder.
+    return_all_encoder_outputs: Whether to output sequence embedding outputs of
+      all encoder transformer layers.
+    output_range: The sequence output range, [0, output_range), by slicing the
+      target sequence of the last transformer layer. `None` means the entire
+      target sequence will attend to the source sequence, which yeilds the full
+      output.
+    embedding_width: The width of the word embeddings. If the embedding width is
+      not equal to hidden size, embedding parameters will be factorized into two
+      matrices in the shape of ['vocab_size', 'embedding_width'] and
+      ['embedding_width', 'hidden_size'] ('embedding_width' is usually much
+      smaller than 'hidden_size').
+  """
+
+  def __init__(
+      self,
+      vocab_size,
+      hidden_size=768,
+      num_layers=12,
+      num_attention_heads=12,
+      max_sequence_length=512,
+      type_vocab_size=16,
+      inner_dim=3072,
+      inner_activation=lambda x: tf.keras.activations.gelu(x, approximate=True),
+      output_dropout=0.1,
+      attention_dropout=0.1,
+      initializer=tf.keras.initializers.TruncatedNormal(stddev=0.02),
+      return_all_encoder_outputs=False,
+      output_range=None,
+      embedding_width=None,
+      **kwargs):
+    activation = tf.keras.activations.get(inner_activation)
+    initializer = tf.keras.initializers.get(initializer)
+
+    self._self_setattr_tracking = False
+    self._config_dict = {
+        'vocab_size': vocab_size,
+        'hidden_size': hidden_size,
+        'num_layers': num_layers,
+        'num_attention_heads': num_attention_heads,
+        'max_sequence_length': max_sequence_length,
+        'type_vocab_size': type_vocab_size,
+        'inner_dim': inner_dim,
+        'inner_activation': tf.keras.activations.serialize(activation),
+        'output_dropout': output_dropout,
+        'attention_dropout': attention_dropout,
+        'initializer': tf.keras.initializers.serialize(initializer),
+        'return_all_encoder_outputs': return_all_encoder_outputs,
+        'output_range': output_range,
+        'embedding_width': embedding_width,
+    }
+
+    word_ids = tf.keras.layers.Input(
+        shape=(None,), dtype=tf.int32, name='input_word_ids')
+    mask = tf.keras.layers.Input(
+        shape=(None,), dtype=tf.int32, name='input_mask')
+    type_ids = tf.keras.layers.Input(
+        shape=(None,), dtype=tf.int32, name='input_type_ids')
+
+    if embedding_width is None:
+      embedding_width = hidden_size
+    self._embedding_layer = self._build_embedding_layer()
+    word_embeddings = self._embedding_layer(word_ids)
+
+    # Always uses dynamic slicing for simplicity.
+    self._position_embedding_layer = layers.PositionEmbedding(
+        initializer=initializer,
+        max_length=max_sequence_length,
+        name='position_embedding')
+    position_embeddings = self._position_embedding_layer(word_embeddings)
+    self._type_embedding_layer = layers.OnDeviceEmbedding(
+        vocab_size=type_vocab_size,
+        embedding_width=embedding_width,
+        initializer=initializer,
+        use_one_hot=True,
+        name='type_embeddings')
+    type_embeddings = self._type_embedding_layer(type_ids)
+
+    embeddings = tf.keras.layers.Add()(
+        [word_embeddings, position_embeddings, type_embeddings])
+
+    self._embedding_norm_layer = tf.keras.layers.LayerNormalization(
+        name='embeddings/layer_norm', axis=-1, epsilon=1e-12, dtype=tf.float32)
+
+    embeddings = self._embedding_norm_layer(embeddings)
+    embeddings = (tf.keras.layers.Dropout(rate=output_dropout)(embeddings))
+
+    # We project the 'embedding' output to 'hidden_size' if it is not already
+    # 'hidden_size'.
+    if embedding_width != hidden_size:
+      self._embedding_projection = tf.keras.layers.experimental.EinsumDense(
+          '...x,xy->...y',
+          output_shape=hidden_size,
+          bias_axes='y',
+          kernel_initializer=initializer,
+          name='embedding_projection')
+      embeddings = self._embedding_projection(embeddings)
+
+    self._transformer_layers = []
+    data = embeddings
+    attention_mask = layers.SelfAttentionMask()(data, mask)
+    encoder_outputs = []
+    for i in range(num_layers):
+      if i == num_layers - 1 and output_range is not None:
+        transformer_output_range = output_range
+      else:
+        transformer_output_range = None
+      layer = layers.TransformerEncoderBlock(
+          num_attention_heads=num_attention_heads,
+          inner_dim=inner_dim,
+          inner_activation=inner_activation,
+          output_dropout=output_dropout,
+          attention_dropout=attention_dropout,
+          output_range=transformer_output_range,
+          kernel_initializer=initializer,
+          name='transformer/layer_%d' % i)
+      self._transformer_layers.append(layer)
+      data = layer([data, attention_mask])
+      encoder_outputs.append(data)
+
+    first_token_tensor = (
+        tf.keras.layers.Lambda(lambda x: tf.squeeze(x[:, 0:1, :], axis=1))(
+            encoder_outputs[-1]))
+    self._pooler_layer = tf.keras.layers.Dense(
+        units=hidden_size,
+        activation='tanh',
+        kernel_initializer=initializer,
+        name='pooler_transform')
+    cls_output = self._pooler_layer(first_token_tensor)
+
+    outputs = dict(
+        sequence_output=encoder_outputs[-1],
+        pooled_output=cls_output,
+        encoder_outputs=encoder_outputs,
+    )
+    super(BertEncoder, self).__init__(
+        inputs=[word_ids, mask, type_ids], outputs=outputs, **kwargs)
+
+  def get_embedding_table(self):
+    return self._embedding_layer.embeddings
+
+  def _build_embedding_layer(self):
+    embedding_width = self._config_dict[
+        'embedding_width'] or self._config_dict['hidden_size']
+    return layers.OnDeviceEmbedding(
+        vocab_size=self._config_dict['vocab_size'],
+        embedding_width=embedding_width,
+        initializer=self._config_dict['initializer'],
+        name='word_embeddings')
+
+  def get_embedding_layer(self):
+    return self._embedding_layer
+
+  def get_config(self):
+    return self._config_dict
+
+  @property
+  def transformer_layers(self):
+    """List of Transformer layers in the encoder."""
+    return self._transformer_layers
+
+  @property
+  def pooler_layer(self):
+    """The pooler dense layer after the transformer layers."""
+    return self._pooler_layer
+
+  @classmethod
+  def from_config(cls, config, custom_objects=None):
+    return cls(**config)

official/nlp/keras_nlp/encoders/bert_encoder_test.py

+# Copyright 2019 The TensorFlow Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Tests for transformer-based bert encoder network."""
+
+# Import libraries
+from absl.testing import parameterized
+import numpy as np
+import tensorflow as tf
+
+from tensorflow.python.keras import keras_parameterized  # pylint: disable=g-direct-tensorflow-import
+from official.nlp.keras_nlp.encoders import bert_encoder
+
+
+# This decorator runs the test in V1, V2-Eager, and V2-Functional mode. It
+# guarantees forward compatibility of this code for the V2 switchover.
+@keras_parameterized.run_all_keras_modes
+class BertEncoderTest(keras_parameterized.TestCase):
+
+  def tearDown(self):
+    super(BertEncoderTest, self).tearDown()
+    tf.keras.mixed_precision.experimental.set_policy("float32")
+
+  def test_network_creation(self):
+    hidden_size = 32
+    sequence_length = 21
+    # Create a small BertEncoder for testing.
+    test_network = bert_encoder.BertEncoder(
+        vocab_size=100,
+        hidden_size=hidden_size,
+        num_attention_heads=2,
+        num_layers=3)
+    # Create the inputs (note that the first dimension is implicit).
+    word_ids = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    mask = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    type_ids = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    dict_outputs = test_network([word_ids, mask, type_ids])
+    data = dict_outputs["sequence_output"]
+    pooled = dict_outputs["pooled_output"]
+
+    self.assertIsInstance(test_network.transformer_layers, list)
+    self.assertLen(test_network.transformer_layers, 3)
+    self.assertIsInstance(test_network.pooler_layer, tf.keras.layers.Dense)
+
+    expected_data_shape = [None, sequence_length, hidden_size]
+    expected_pooled_shape = [None, hidden_size]
+    self.assertAllEqual(expected_data_shape, data.shape.as_list())
+    self.assertAllEqual(expected_pooled_shape, pooled.shape.as_list())
+
+    # The default output dtype is float32.
+    self.assertAllEqual(tf.float32, data.dtype)
+    self.assertAllEqual(tf.float32, pooled.dtype)
+
+  def test_all_encoder_outputs_network_creation(self):
+    hidden_size = 32
+    sequence_length = 21
+    # Create a small BertEncoder for testing.
+    test_network = bert_encoder.BertEncoder(
+        vocab_size=100,
+        hidden_size=hidden_size,
+        num_attention_heads=2,
+        num_layers=3,
+        return_all_encoder_outputs=True)
+    # Create the inputs (note that the first dimension is implicit).
+    word_ids = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    mask = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    type_ids = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    dict_outputs = test_network([word_ids, mask, type_ids])
+    all_encoder_outputs = dict_outputs["encoder_outputs"]
+    pooled = dict_outputs["pooled_output"]
+
+    expected_data_shape = [None, sequence_length, hidden_size]
+    expected_pooled_shape = [None, hidden_size]
+    self.assertLen(all_encoder_outputs, 3)
+    for data in all_encoder_outputs:
+      self.assertAllEqual(expected_data_shape, data.shape.as_list())
+    self.assertAllEqual(expected_pooled_shape, pooled.shape.as_list())
+
+    # The default output dtype is float32.
+    self.assertAllEqual(tf.float32, all_encoder_outputs[-1].dtype)
+    self.assertAllEqual(tf.float32, pooled.dtype)
+
+  def test_network_creation_with_float16_dtype(self):
+    hidden_size = 32
+    sequence_length = 21
+    tf.keras.mixed_precision.experimental.set_policy("mixed_float16")
+    # Create a small BertEncoder for testing.
+    test_network = bert_encoder.BertEncoder(
+        vocab_size=100,
+        hidden_size=hidden_size,
+        num_attention_heads=2,
+        num_layers=3)
+    # Create the inputs (note that the first dimension is implicit).
+    word_ids = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    mask = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    type_ids = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    dict_outputs = test_network([word_ids, mask, type_ids])
+    data = dict_outputs["sequence_output"]
+    pooled = dict_outputs["pooled_output"]
+
+    expected_data_shape = [None, sequence_length, hidden_size]
+    expected_pooled_shape = [None, hidden_size]
+    self.assertAllEqual(expected_data_shape, data.shape.as_list())
+    self.assertAllEqual(expected_pooled_shape, pooled.shape.as_list())
+
+    # If float_dtype is set to float16, the data output is float32 (from a layer
+    # norm) and pool output should be float16.
+    self.assertAllEqual(tf.float32, data.dtype)
+    self.assertAllEqual(tf.float16, pooled.dtype)
+
+  @parameterized.named_parameters(
+      ("all_sequence", None, 21),
+      ("output_range", 1, 1),
+  )
+  def test_network_invocation(self, output_range, out_seq_len):
+    hidden_size = 32
+    sequence_length = 21
+    vocab_size = 57
+    num_types = 7
+    # Create a small BertEncoder for testing.
+    test_network = bert_encoder.BertEncoder(
+        vocab_size=vocab_size,
+        hidden_size=hidden_size,
+        num_attention_heads=2,
+        num_layers=3,
+        type_vocab_size=num_types,
+        output_range=output_range)
+    # Create the inputs (note that the first dimension is implicit).
+    word_ids = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    mask = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    type_ids = tf.keras.Input(shape=(sequence_length,), dtype=tf.int32)
+    dict_outputs = test_network([word_ids, mask, type_ids])
+    data = dict_outputs["sequence_output"]
+    pooled = dict_outputs["pooled_output"]
+
+    # Create a model based off of this network:
+    model = tf.keras.Model([word_ids, mask, type_ids], [data, pooled])
+
+    # Invoke the model. We can't validate the output data here (the model is too
+    # complex) but this will catch structural runtime errors.
+    batch_size = 3
+    word_id_data = np.random.randint(
+        vocab_size, size=(batch_size, sequence_length))
+    mask_data = np.random.randint(2, size=(batch_size, sequence_length))
+    type_id_data = np.random.randint(
+        num_types, size=(batch_size, sequence_length))
+    outputs = model.predict([word_id_data, mask_data, type_id_data])
+    self.assertEqual(outputs[0].shape[1], out_seq_len)
+
+    # Creates a BertEncoder with max_sequence_length != sequence_length
+    max_sequence_length = 128
+    test_network = bert_encoder.BertEncoder(
+        vocab_size=vocab_size,
+        hidden_size=hidden_size,
+        max_sequence_length=max_sequence_length,
+        num_attention_heads=2,
+        num_layers=3,
+        type_vocab_size=num_types)
+    dict_outputs = test_network([word_ids, mask, type_ids])
+    data = dict_outputs["sequence_output"]
+    pooled = dict_outputs["pooled_output"]
+    model = tf.keras.Model([word_ids, mask, type_ids], [data, pooled])
+    outputs = model.predict([word_id_data, mask_data, type_id_data])
+    self.assertEqual(outputs[0].shape[1], sequence_length)
+
+    # Creates a BertEncoder with embedding_width != hidden_size
+    test_network = bert_encoder.BertEncoder(
+        vocab_size=vocab_size,
+        hidden_size=hidden_size,
+        max_sequence_length=max_sequence_length,
+        num_attention_heads=2,
+        num_layers=3,
+        type_vocab_size=num_types,
+        embedding_width=16)
+    dict_outputs = test_network([word_ids, mask, type_ids])
+    data = dict_outputs["sequence_output"]
+    pooled = dict_outputs["pooled_output"]
+    model = tf.keras.Model([word_ids, mask, type_ids], [data, pooled])
+    outputs = model.predict([word_id_data, mask_data, type_id_data])
+    self.assertEqual(outputs[0].shape[-1], hidden_size)
+    self.assertTrue(hasattr(test_network, "_embedding_projection"))
+
+  def test_serialize_deserialize(self):
+    # Create a network object that sets all of its config options.
+    kwargs = dict(
+        vocab_size=100,
+        hidden_size=32,
+        num_layers=3,
+        num_attention_heads=2,
+        max_sequence_length=21,
+        type_vocab_size=12,
+        inner_dim=1223,
+        inner_activation="relu",
+        output_dropout=0.05,
+        attention_dropout=0.22,
+        initializer="glorot_uniform",
+        return_all_encoder_outputs=False,
+        output_range=-1,
+        embedding_width=16)
+    network = bert_encoder.BertEncoder(**kwargs)
+    expected_config = dict(kwargs)
+    expected_config["inner_activation"] = tf.keras.activations.serialize(
+        tf.keras.activations.get(expected_config["inner_activation"]))
+    expected_config["initializer"] = tf.keras.initializers.serialize(
+        tf.keras.initializers.get(expected_config["initializer"]))
+    self.assertEqual(network.get_config(), expected_config)
+    # Create another network object from the first object's config.
+    new_network = bert_encoder.BertEncoder.from_config(network.get_config())
+
+    # Validate that the config can be forced to JSON.
+    _ = network.to_json()
+
+    # If the serialization was successful, the new config should match the old.
+    self.assertAllEqual(network.get_config(), new_network.get_config())
+
+    # Tests model saving/loading.
+    model_path = self.get_temp_dir() + "/model"
+    network.save(model_path)
+    _ = tf.keras.models.load_model(model_path)
+
+
+if __name__ == "__main__":
+  tf.test.main()