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--- |
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language: en |
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tags: |
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- exbert |
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license: apache-2.0 |
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datasets: |
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- bookcorpus |
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- wikipedia |
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base_model: google-bert/bert-base-uncased |
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--- |
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# BERT base model (cased) |
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Pretrained model on English language using a masked language modeling (MLM) objective. It was introduced in |
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[this paper](https://arxiv.org/abs/1810.04805) and first released in |
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[this repository](https://github.com/google-research/bert). This model is case-sensitive: it makes a difference between |
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english and English. |
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Disclaimer: The team releasing BERT did not write a model card for this model so this model card has been written by |
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the Hugging Face team. |
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## Model description |
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BERT is a transformers model pretrained on a large corpus of English data in a self-supervised fashion. This means it |
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was pretrained on the raw texts only, with no humans labelling them in any way (which is why it can use lots of |
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publicly available data) with an automatic process to generate inputs and labels from those texts. More precisely, it |
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was pretrained with two objectives: |
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- Masked language modeling (MLM): taking a sentence, the model randomly masks 15% of the words in the input then run |
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the entire masked sentence through the model and has to predict the masked words. This is different from traditional |
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recurrent neural networks (RNNs) that usually see the words one after the other, or from autoregressive models like |
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GPT which internally mask the future tokens. It allows the model to learn a bidirectional representation of the |
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sentence. |
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- Next sentence prediction (NSP): the models concatenates two masked sentences as inputs during pretraining. Sometimes |
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they correspond to sentences that were next to each other in the original text, sometimes not. The model then has to |
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predict if the two sentences were following each other or not. |
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This way, the model learns an inner representation of the English language that can then be used to extract features |
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useful for downstream tasks: if you have a dataset of labeled sentences for instance, you can train a standard |
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classifier using the features produced by the BERT model as inputs. |
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## Intended uses & limitations |
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You can use the raw model for either masked language modeling or next sentence prediction, but it's mostly intended to |
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be fine-tuned on a downstream task. See the [model hub](https://huggingface.co/models?filter=bert) to look for |
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fine-tuned versions on a task that interests you. |
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Note that this model is primarily aimed at being fine-tuned on tasks that use the whole sentence (potentially masked) |
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to make decisions, such as sequence classification, token classification or question answering. For tasks such as text |
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generation you should look at model like GPT2. |
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### How to use |
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You can use this model directly with a pipeline for masked language modeling: |
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```python |
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>>> from transformers import pipeline |
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>>> unmasker = pipeline('fill-mask', model='bert-base-cased') |
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>>> unmasker("Hello I'm a [MASK] model.") |
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[{'sequence': "[CLS] Hello I'm a fashion model. [SEP]", |
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'score': 0.09019174426794052, |
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'token': 4633, |
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'token_str': 'fashion'}, |
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{'sequence': "[CLS] Hello I'm a new model. [SEP]", |
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'score': 0.06349995732307434, |
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'token': 1207, |
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'token_str': 'new'}, |
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{'sequence': "[CLS] Hello I'm a male model. [SEP]", |
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'score': 0.06228214129805565, |
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'token': 2581, |
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'token_str': 'male'}, |
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{'sequence': "[CLS] Hello I'm a professional model. [SEP]", |
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'score': 0.0441727414727211, |
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'token': 1848, |
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'token_str': 'professional'}, |
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{'sequence': "[CLS] Hello I'm a super model. [SEP]", |
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'score': 0.03326151892542839, |
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'token': 7688, |
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'token_str': 'super'}] |
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``` |
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Here is how to use this model to get the features of a given text in PyTorch: |
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```python |
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from transformers import BertTokenizer, BertModel |
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tokenizer = BertTokenizer.from_pretrained('bert-base-cased') |
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model = BertModel.from_pretrained("bert-base-cased") |
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text = "Replace me by any text you'd like." |
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encoded_input = tokenizer(text, return_tensors='pt') |
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output = model(**encoded_input) |
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``` |
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and in TensorFlow: |
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```python |
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from transformers import BertTokenizer, TFBertModel |
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tokenizer = BertTokenizer.from_pretrained('bert-base-cased') |
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model = TFBertModel.from_pretrained("bert-base-cased") |
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text = "Replace me by any text you'd like." |
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encoded_input = tokenizer(text, return_tensors='tf') |
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output = model(encoded_input) |
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``` |
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### Limitations and bias |
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Even if the training data used for this model could be characterized as fairly neutral, this model can have biased |
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predictions: |
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```python |
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>>> from transformers import pipeline |
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>>> unmasker = pipeline('fill-mask', model='bert-base-cased') |
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>>> unmasker("The man worked as a [MASK].") |
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[{'sequence': '[CLS] The man worked as a lawyer. [SEP]', |
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'score': 0.04804691672325134, |
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'token': 4545, |
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'token_str': 'lawyer'}, |
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{'sequence': '[CLS] The man worked as a waiter. [SEP]', |
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'score': 0.037494491785764694, |
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'token': 17989, |
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'token_str': 'waiter'}, |
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{'sequence': '[CLS] The man worked as a cop. [SEP]', |
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'score': 0.035512614995241165, |
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'token': 9947, |
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'token_str': 'cop'}, |
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{'sequence': '[CLS] The man worked as a detective. [SEP]', |
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'score': 0.031271643936634064, |
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'token': 9140, |
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'token_str': 'detective'}, |
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{'sequence': '[CLS] The man worked as a doctor. [SEP]', |
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'score': 0.027423162013292313, |
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'token': 3995, |
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'token_str': 'doctor'}] |
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>>> unmasker("The woman worked as a [MASK].") |
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[{'sequence': '[CLS] The woman worked as a nurse. [SEP]', |
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'score': 0.16927455365657806, |
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'token': 7439, |
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'token_str': 'nurse'}, |
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{'sequence': '[CLS] The woman worked as a waitress. [SEP]', |
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'score': 0.1501094549894333, |
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'token': 15098, |
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'token_str': 'waitress'}, |
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{'sequence': '[CLS] The woman worked as a maid. [SEP]', |
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'score': 0.05600163713097572, |
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'token': 13487, |
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'token_str': 'maid'}, |
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{'sequence': '[CLS] The woman worked as a housekeeper. [SEP]', |
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'score': 0.04838843643665314, |
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'token': 26458, |
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'token_str': 'housekeeper'}, |
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{'sequence': '[CLS] The woman worked as a cook. [SEP]', |
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'score': 0.029980547726154327, |
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'token': 9834, |
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'token_str': 'cook'}] |
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``` |
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This bias will also affect all fine-tuned versions of this model. |
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## Training data |
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The BERT model was pretrained on [BookCorpus](https://yknzhu.wixsite.com/mbweb), a dataset consisting of 11,038 |
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unpublished books and [English Wikipedia](https://en.wikipedia.org/wiki/English_Wikipedia) (excluding lists, tables and |
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headers). |
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## Training procedure |
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### Preprocessing |
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The texts are tokenized using WordPiece and a vocabulary size of 30,000. The inputs of the model are then of the form: |
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``` |
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[CLS] Sentence A [SEP] Sentence B [SEP] |
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``` |
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With probability 0.5, sentence A and sentence B correspond to two consecutive sentences in the original corpus and in |
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the other cases, it's another random sentence in the corpus. Note that what is considered a sentence here is a |
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consecutive span of text usually longer than a single sentence. The only constrain is that the result with the two |
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"sentences" has a combined length of less than 512 tokens. |
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The details of the masking procedure for each sentence are the following: |
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- 15% of the tokens are masked. |
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- In 80% of the cases, the masked tokens are replaced by `[MASK]`. |
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- In 10% of the cases, the masked tokens are replaced by a random token (different) from the one they replace. |
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- In the 10% remaining cases, the masked tokens are left as is. |
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### Pretraining |
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The model was trained on 4 cloud TPUs in Pod configuration (16 TPU chips total) for one million steps with a batch size |
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of 256. The sequence length was limited to 128 tokens for 90% of the steps and 512 for the remaining 10%. The optimizer |
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used is Adam with a learning rate of 1e-4, \\(\beta_{1} = 0.9\\) and \\(\beta_{2} = 0.999\\), a weight decay of 0.01, |
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learning rate warmup for 10,000 steps and linear decay of the learning rate after. |
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## Evaluation results |
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When fine-tuned on downstream tasks, this model achieves the following results: |
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Glue test results: |
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| Task | MNLI-(m/mm) | QQP | QNLI | SST-2 | CoLA | STS-B | MRPC | RTE | Average | |
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|:----:|:-----------:|:----:|:----:|:-----:|:----:|:-----:|:----:|:----:|:-------:| |
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| | 84.6/83.4 | 71.2 | 90.5 | 93.5 | 52.1 | 85.8 | 88.9 | 66.4 | 79.6 | |
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### BibTeX entry and citation info |
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```bibtex |
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@article{DBLP:journals/corr/abs-1810-04805, |
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author = {Jacob Devlin and |
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Ming{-}Wei Chang and |
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Kenton Lee and |
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Kristina Toutanova}, |
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title = {{BERT:} Pre-training of Deep Bidirectional Transformers for Language |
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Understanding}, |
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journal = {CoRR}, |
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volume = {abs/1810.04805}, |
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year = {2018}, |
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url = {http://arxiv.org/abs/1810.04805}, |
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archivePrefix = {arXiv}, |
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eprint = {1810.04805}, |
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timestamp = {Tue, 30 Oct 2018 20:39:56 +0100}, |
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biburl = {https://dblp.org/rec/journals/corr/abs-1810-04805.bib}, |
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bibsource = {dblp computer science bibliography, https://dblp.org} |
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} |
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``` |
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<a href="https://huggingface.co/exbert/?model=bert-base-cased"> |
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<img width="300px" src="https://cdn-media.huggingface.co/exbert/button.png"> |
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</a> |
