Training a sentence planner for spoken dialogue using boosting

In the past few years, as the number of dialogue systems has increased, there has been an increasing interest in the use of natural language generation in spoken dialogue. Our research assumes that trainable natural language generation is needed to support more flexible and customized dialogues with human users. This paper focuses on methods for automatically training the sentence planning module of a spoken language generator. Sentence planning is a set of inter-related but distinct tasks, one of which is sentence scoping, i.e., the choice of syntactic structure for elementary speech acts and the decision of how to combine them into one or more sentences. The paper first presents SPoT, a trainable sentence planner, and a new methodology for automatically training SPoT on the basis of feedback provided by human judges. Our methodology is unique in neither depending on hand-crafted rules nor on the existence of a domain-specific corpus. SPoT first randomly generates a candidate set of sentence plans and then selects one. We show that SPoT learns to select a sentence plan whose rating on average is only 5% worse than the top human-ranked sentence plan. We then experimentally evaluate SPoT by asking human judges to compare SPoT's output with a hand-crafted template-based generation component, two rule-based sentence planners, and two baseline sentence planners. We show that SPoT performs better than the rule-based systems and the baselines, and as well as the hand-crafted system.