In dialogue systems, a dialogue state tracker aims to accurately find a
compact representation of the current dialogue status, based on the entire
dialogue history. While previous approaches often define dialogue states as a
combination of separate triples ({\em domain-slot-value}), in this paper, we
employ a structured state representation and cast dialogue state tracking as a
sequence generation problem. Based on this new formulation, we propose a {\bf
C}oa{\bf R}s{\bf E}-to-fine {\bf DI}alogue state {\bf T}racking ({\bf CREDIT})
approach. Taking advantage of the structured state representation, which is a
marked language sequence, we can further fine-tune the pre-trained model (by
supervised learning) by optimizing natural language metrics with the policy
gradient method. Like all generative state tracking methods, CREDIT does not
rely on pre-defined dialogue ontology enumerating all possible slot values.
Experiments demonstrate our tracker achieves encouraging joint goal accuracy
for the five domains in MultiWOZ 2.0 and MultiWOZ 2.1 datasets.

本文提出了一种基于结构化状态表征的、称为 Coarse-to-fine Dialogue State Tracking (CREDIT) 的方法，它将对话状态跟踪作为序列生成问题，并在 MultiWOZ 数据集上获得了令人满意的实验结果。