An Explainable Collaborative Dialogue System using a Theory of Mind

Eva is a neuro-symbolic domain-independent multimodal collaborative dialogue system that takes seriously that the purpose of task-oriented dialogue is to assist the user. To do this, the system collaborates by inferring their intentions and plans, detects obstacles to success, finds plans to overcome them or to achieve higher-level goals, and plans its actions, including speech acts, to help users accomplish those goals. In doing so, the system maintains and reasons with its own declaratively-specified beliefs, goals and intentions, and explicitly reasons about those of its user. Because Eva can track different users' mental states, it can engage multiple agents in multi-party dialogues. Reasoning is accomplished with a modal Horn-clause meta-interpreter that enables computable inference within the subset of logic implemented. The system employs both hierarchical and backward-chaining planning, operating over a rich modal logic-based knowledge and action representation. The planning and reasoning subsystems obey the principles of persistent goals and intentions including: 1) The formation and decomposition of intentions to perform complex actions, 2) the conditions under which persistent goals and intentions can be given up, and 3) persistent goal and intention revision using the relativizing formulas that are created during the planning process. The system treats its speech acts just like its other actions. This general approach enables Eva to plan a variety of speech acts, including requests, informs, questions, confirmations, offers, acceptances, and emotive expressions. Because the dialogue engine is a planner, as the dialogue proceeds, the system can flexibly generate, execute, and potentially repair its plans using physical, digital, and speech actions. Importantly, Eva can explain its utterances because it has created a plan that caused it to utter them.