This thesis presents a mixed-initiative response generation model in a task- execution dialog system. Target domain is task-execution dialog system and target conversation style is mixed-initiative dialog. The model uses plan- based dialog processing model in order to trace user's underlying plans and to select system agent's plans. This was done by enhancing current plan-based dialog model in dialog understanding field and making system agent's planning strategies.
In task-execution dialog, both user and system agent have different goals and perform their own task-related plans while they try to accomplish their own goals during the conversation. The proposed dialog processing model uses individual plans rather than a joint plan to the domain and problem-solving levels, and keeps maintain separated contexts of user and system agent. Thus the system agent's problem-solving actions can be made independently from communicative situations and therefore, can deal with mixed-initiative interactions. If the system agent is operating under some joint plan, it can deal with only altruistic style reactions. The model needed two major decision heuristics to make system agent's plans. One is about controlling task-execution flow in problem-solving level and the other is about making dialog sentence in communicative level.
The proposed model can do two different kinds of reaction and select system agent's task-related plans. To do this, the model classifies the problem-solving actions and specifies the sequence of applying plan library with a view to reaction styles. The introduction of problem-solving level interactions enables the proposed model to deal with mixed-initiative interactions effectively and simplifies a consistent control flow for task-execution dialogs.
In a conversation, ellipsis and anaphora are the main tools of reflecting the context appropriately. This model suggests a decision strategy of applying ellipsis and anaphora with a viewpoint of context-intimacy in the dialog sentence generation. The decision of the context-intimacy is made on every word of a response sentence. The context-intimacy is either distinctive or intimate. If a word is a part of a context, then the context-intimacy of a word with that context is intimate and otherwise it is distinctive. The surface form of a word is decided differently according to whether the context neighbors with the word or not. Considering this, we suggests two evaluation criteria, one for the neighboring context and the other for the separated context.