TOD-BERT: Pre-trained Natural Language Understanding for Task-Oriented Dialogue
Written for the Research library (claude-opus-5-5) from the paper text. Original — aclanthology.org/2020.emnlp-main.66.pdf
Summary
Language models pre-trained on general text such as Wikipedia or books transfer poorly to task-oriented dialogue. Conversation differs linguistically from written prose, and individual task-oriented corpora are small and scattered. To close this gap, the authors merge nine English, human-human, multi-turn task-oriented dialogue datasets into one pre-training corpus. They then continue training BERT-base on it, producing TOD-BERT. Two changes adapt the model to dialogue. First, special speaker tokens mark each user turn and each system turn. Second, standard masked language modeling is paired with a response contrastive loss that imitates response selection. With only minimal added components, the model is fine-tuned for four downstream tasks: classifying user intents, tracking the state of the dialogue, predicting the acts of dialogue turns, and choosing the correct response. On all four, TOD-BERT beats BERT, GPT-2 and DialoGPT. Its advantage is especially large when only a small portion of the labeled data is available. This matters because annotated task-oriented data is costly to collect. The model also works as a drop-in encoder for existing dialogue systems.
Key points
- The unified pre-training corpus covers 100,707 dialogues and about 1.39M utterances across more than 60 domains. Its sources are MetaLWOZ, Schema, Taskmaster, MWOZ, MSR-E2E, SMD, Frames, WOZ and CamRest676.
- The architecture is BERT-base uncased (12 layers, 12 heads, hidden size 768) with added [USR] and [SYS] tokens. Training uses MLM alone (TOD-BERT-mlm) or MLM plus response contrastive loss (TOD-BERT-jnt).
- In response selection on MWOZ, TOD-BERT-jnt achieves 65.8% 1-to-100 and 87.0% 3-to-100 accuracy. This is 18.3 and 11.5 points above BERT, with similar gains on DSTC2 and GSIM.
- In few-shot dialogue act prediction with 1% of MWOZ training data, TOD-BERT-mlm exceeds BERT by 3.5 micro-F1 and 6.6 macro-F1.
- K-means clustering of system-response embeddings matches MWOZ domain labels better for TOD-BERT than for BERT. NMI is 0.143 vs 0.094 at K=10 and 0.213 vs 0.109 at K=20. Code is available at github.com/jasonwu0731/ToD-BERT.
Cited by
Cite
@inproceedings{wu2020tod,
title = {{TOD-BERT: Pre-trained Natural Language Understanding for Task-Oriented Dialogue}},
author = {Wu, Chien-Sheng and Hoi, Steven C.H. and Socher, Richard and Xiong, Caiming},
booktitle = {Proceedings of the 2020 Conference on Empirical Methods in Natural Language Processing (EMNLP)},
year = {2020},
doi = {10.18653/v1/2020.emnlp-main.66},
url = {https://doi.org/10.18653/v1/2020.emnlp-main.66}
}References
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