Sequicity: Simplifying Task-oriented Dialogue Systems with Single Sequence-to-Sequence Architectures
Summary
Conventional task-oriented dialogue systems chain separate modules, and the belief tracker is the weakest link. It typically uses one classifier per slot, which grows heavy as slots and values multiply. It also cannot recognise slot values unseen in training, depends on delexicalisation, and must be pre-trained apart from the rest of the system. Lei et al. replace this pipeline with Sequicity, a framework built on a single seq2seq model. Its central idea is the belief span (bspan): a short text segment, with <Inf> and <Req> fields, that the model writes out at each turn to record constraints and requested slots. Under a Markov assumption, the model reads only the previous bspan, the previous system reply and the current user utterance. It then decodes in two steps: first the new bspan, which drives the knowledge base lookup, then the reply, conditioned on the bspan and the lookup result. The authors build this as Two Stage CopyNet (TSCP) and train it with supervised learning plus optional reinforcement learning. On CamRes676 and KVRET, TSCP beats pipeline baselines in both task success and language quality. It is also roughly ten times smaller and faster to train, and it still works when slot values are out-of-vocabulary.
Key points
- Sequicity frames dialogue state tracking and response generation as one sequence-generation problem, so the whole system is trained end to end with no separately pre-trained tracker.
- TSCP extends CopyNet (Gu et al., 2016), since words in bspans and replies are often copied from earlier utterances. Reinforcement learning fine-tuning raises both BLEU and success F1 at modest extra training cost.
- Evaluation uses CamRes676 and KVRET. In OOV stress tests, the pipeline baseline NDM collapses, while TSCP keeps a reasonable entity match rate because it learns sentence patterns rather than fixed value labels.
- On KVRET, the authors grow the slot inventory through 79, 144 and 284 distinct slot values by adding domains. TSCP's parameter count stays about an order of magnitude below NDM's and is far less sensitive to this growth.
- Source code is released at github.com/WING-NUS/sequicity. A simple post-processing script helps handle users who change their minds, but only when slot values are predefined.
Cited by
- In-Context Learning for Few-Shot Dialogue State Tracking
- Efficient Dialogue State Tracking by Selectively Overwriting Memory
- MinTL: Minimalist Transfer Learning for Task-Oriented Dialogue Systems
- TRACER: Early Failure Detection for Task-Oriented Dialogue
- Find or Classify? Dual Strategy for Slot-Value Predictions on Multi-Domain Dialog State Tracking
- TAT-QA: A Question Answering Benchmark on a Hybrid of Tabular and Textual Content in Finance
Cite
@inproceedings{lei2018sequicity,
title = {{Sequicity: Simplifying Task-oriented Dialogue Systems with Single Sequence-to-Sequence Architectures}},
author = {Lei, Wenqiang and Jin, Xisen and Kan, Min-Yen and Ren, Zhaochun and He, Xiangnan and Yin, Dawei},
booktitle = {Proceedings of the 56th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)},
year = {2018},
doi = {10.18653/v1/p18-1133},
url = {https://doi.org/10.18653/v1/p18-1133}
}References
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