Conversational Search with Mixed-Initiative -- Asking Good Clarification Questions backed-up by Passage Retrieval

We deal with a scenario of conversational search with mixed-initiative: namely user-asks system-answers, as well as system-asks (clarification questions) and user-answers. We focus on the task of selecting the next clarification question, given conversation context. Our method leverages passage retrieval that is used both for an initial selection of relevant candidate clarification questions, as well as for fine-tuning two deep-learning models for re-ranking these candidates. We evaluated our method on two different use-cases. The first is an open domain conversational search in a large web collection. The second is a task-oriented customer-support setup. We show that our method performs well on both use-cases.