Hierarchical Transformer for Task Oriented Dialog Systems

Bishal Santra, Potnuru Anusha, Pawan Goyal


Abstract
Generative models for dialog systems have gained much interest because of the recent success of RNN and Transformer based models in tasks like question answering and summarization. Although the task of dialog response generation is generally seen as a sequence to sequence (Seq2Seq) problem, researchers in the past have found it challenging to train dialog systems using the standard Seq2Seq models. Therefore, to help the model learn meaningful utterance and conversation level features, Sordoni et al. (2015b), Serban et al. (2016) proposed Hierarchical RNN architecture, which was later adopted by several other RNN based dialog systems. With the transformer-based models dominating the seq2seq problems lately, the natural question to ask is the applicability of the notion of hierarchy in transformer-based dialog systems. In this paper, we propose a generalized framework for Hierarchical Transformer Encoders and show how a standard transformer can be morphed into any hierarchical encoder, including HRED and HIBERT like models, by using specially designed attention masks and positional encodings. We demonstrate that Hierarchical Encoding helps achieve better natural language understanding of the contexts in transformer-based models for task-oriented dialog systems through a wide range of experiments.
Anthology ID:
2021.naacl-main.449
Volume:
Proceedings of the 2021 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies
Month:
June
Year:
2021
Address:
Online
Editors:
Kristina Toutanova, Anna Rumshisky, Luke Zettlemoyer, Dilek Hakkani-Tur, Iz Beltagy, Steven Bethard, Ryan Cotterell, Tanmoy Chakraborty, Yichao Zhou
Venue:
NAACL
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
5649–5658
Language:
URL:
https://aclanthology.org/2021.naacl-main.449
DOI:
10.18653/v1/2021.naacl-main.449
Bibkey:
Cite (ACL):
Bishal Santra, Potnuru Anusha, and Pawan Goyal. 2021. Hierarchical Transformer for Task Oriented Dialog Systems. In Proceedings of the 2021 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies, pages 5649–5658, Online. Association for Computational Linguistics.
Cite (Informal):
Hierarchical Transformer for Task Oriented Dialog Systems (Santra et al., NAACL 2021)
Copy Citation:
PDF:
https://aclanthology.org/2021.naacl-main.449.pdf
Video:
 https://aclanthology.org/2021.naacl-main.449.mp4
Code
 bsantraigi/hier-transformer-pytorch +  additional community code
Data
MultiWOZ