Abstract: The ability of a dialog system to express prespecified language style during conversations has a direct, positive impact on its usability and on user satisfaction. We introduce a new prototype-to-style (PS) framework to tackle the challenge of stylistic dialogue generation. The framework uses an Information Retrieval (IR) system and extracts a response prototype from the retrieved response. A stylistic response generator then takes the prototype and the desired language style as model input to obtain a high-quality and stylistic response. To effectively train the proposed model, we propose a new style-aware learning objective as well as a de-noising learning strategy. Results on three benchmark datasets from two languages demonstrate that the proposed approach significantly outperforms existing baselines in both in-domain and cross-domain evaluations

Introduction: Most early research on dialogue response generation focused on generating grammatical and contextually relevant responses BIBREF0, BIBREF1, BIBREF2. While promising results have been demonstrated BIBREF3, BIBREF4, syntactically coherent responses alone do not guarantee an engaging and attractive dialogue system. Expressing a unique and consistent speaking style has been shown to be crucial for increasing the user's engagement with dialogue systems BIBREF5. There are various definitions of language style BIBREF6, BIBREF7, BIBREF8, BIBREF9, BIBREF10. In this work, from a purely computational standpoint, we refer to language style as any characteristic style of expression. Hence, our work is in line with previous work on dialogue generation with emotion BIBREF11, BIBREF12, BIBREF13, BIBREF14; response attitude BIBREF15, and speaker personality BIBREF16. The aforementioned approaches explicitly incorporate the language style information into the model configuration either via embeddings or memory modules to control the process of response generation. In our replication experiments, we found that these approaches tend to overemphasise the importance of the language style. As a result, the generated responses tend to be generic and non-informative BIBREF17, but they do express a distinct style; e.g., they generate a generic response: “I am happy to hear that." that conveys a `happy' emotion to different queries. In this work, we propose a novel prototype-to-style (PS) framework to tackle the challenge of stylistic dialogue generation. Our motivation is two-fold: (1) Human-written responses are informative and diverse, which could be leveraged as guidance for the generation model; (2) However, the retrieved response is not guaranteed to express the desired language style. Moreover, the quality of the retrieved response varies among different queries due to the instability of the IR system. Therefore, to transform the retrieved result into a relevant and stylistic response, an adequate editing process is necessary. An illustration of the proposed framework is shown in Figure FIGREF2, where a prototype is first extracted from the retrieved response. The stylistic response generator then takes the desired language style and the extracted prototype as additional input to obtain an adequate and stylistic response. The proposed stylistic response generator mainly inherits from the GPT-2 model BIBREF18 which is pre-trained with a large unlabeled text corpus. However, the GPT-2 model does not naturally fit the task of dialogue generation. To this end, we design various adaptations to the model architecture to extend the GPT-2 model to address the task of dialogue generation. Furthermore, in order to control the style of the generated responses, we train the model with a novel style-aware maximum likelihood estimation (MLE) objective that encodes additional style knowledge into the model's parameters. Finally, to mitigate the possible effect that the retrieved response containing irrelevant and inappropriate information with respect to the input query, we adopt a de-noising learning strategy BIBREF19, BIBREF20 to prevent the model from uncritically copying the prototype. To fully evaluate the proposed approach, we conduct extensive experiments on three benchmark datasets. Results of both human and automatic evaluation show that the proposed approach significantly outperforms several strong baselines. In addition, we also conduct an extensive cross-domain experiment to demonstrate that the proposed approach is more robust than such baselines. It should be noted that stylistic dialogue generation is different from the task of text style transfer. Text style transfer aims to rewrite the input sentences such that they possess certain language styles, while rigorously preserving their semantic meaning BIBREF21. On the other hand, stylistic dialogue generation does not aim at preserving the semantic meaning of the input sentences. Instead, it aims at generating sentences that are adequate and relevant responses to the input sentences, while expressing the prespecified language styles. In summary, the contributions of this work are: (1) We propose a novel framework that tackles the challenge of stylistic dialogue generation by leveraging useful information contained in the retrieved responses; (2) We propose a new stylistic response generator by making proper adaptations to a large-scale pre-trained language model. We train our model with a new style-aware learning objective in a de-noising manner. Experiments show that the proposed model outperforms many strong baselines on three benchmark datasets on both in-domain and cross-domain evaluations.

Question: On what two languages is experimented on?
Answer: Chinese and English