BERT 输出说明

Question

BERT编码器输出的key是default、encoder_outputs、pooled_output和sequence_output

据我所知，encoder_outputs是每个encoder的输出，pooled_output是全局上下文的输出，sequence_output是每个token的输出上下文（如果我错了请纠正我）。但是 default 是什么？你能给我一个更详细的解释吗？

This is the link to the encoder

Answer 1

Tensorflow docs 对您询问的输出提供了很好的解释：

The BERT models return a map with 3 important keys: pooled_output, sequence_output, encoder_outputs:

pooled_output represents each input sequence as a whole. The shape is [batch_size, H]. You can think of this as an embedding for the entire movie review.

sequence_output represents each input token in the context. The shape is [batch_size, seq_length, H]. You can think of this as a contextual embedding for every token in the movie review.

encoder_outputs are the intermediate activations of the L Transformer blocks. outputs["encoder_outputs"][i] is a Tensor of shape [batch_size, seq_length, 1024] with the outputs of the i-th Transformer block, for 0 <= i < L. The last value of the list is equal to sequence_output

Here 是另一个关于 pooled_output 和 sequence_output 之间区别的有趣讨论，如果您有兴趣的话。

default 输出等于 pooled_output，您可以在这里确认：

import tensorflow as tf
import tensorflow_hub as hub

tfhub_handle_preprocess = 'https://tfhub.dev/tensorflow/bert_en_uncased_preprocess/3'
tfhub_handle_encoder = 'https://tfhub.dev/tensorflow/small_bert/bert_en_uncased_L-4_H-512_A-8/1'

def build_classifier_model(name):
    text_input = tf.keras.layers.Input(shape=(), dtype=tf.string, name='features')    
    bert_preprocess_model = hub.KerasLayer(tfhub_handle_preprocess, name='preprocessing')
    encoder_inputs = bert_preprocess_model(text_input)
    encoder = hub.KerasLayer(tfhub_handle_encoder) 
    outputs = encoder(encoder_inputs)
    net = outputs[name]
    return tf.keras.Model(text_input, net)

sentence = tf.constant([
"Improve the physical fitness of your goldfish by getting him a bicycle"
])

classifier_model = build_classifier_model(name='default')
default_output = classifier_model(sentence)

classifier_model = build_classifier_model(name='pooled_output')
pooled_output = classifier_model(sentence)

print(default_output == pooled_output)

BERT 输出说明

BERT outputs explained

python

tensorflow

deep-learning

nlp

bert-language-model