A Hybrid Reasoning Model for Indirect Answers

A HYBRID REASONING MODEL FOR INDIRECT ANSWERS Nancy Green Department of Computer Science University of Delaware Newark, DE 19716, USA Internet: green@udel.edu Sandra Carberry Department of Computer Science University of Delaware Visitor: Inst. for Research in Cognitive Science University of Pennsylvania Internet: carberry@udel.edu Abstract This paper presents our implemented computa- tional model for interpreting and generating in- direct answers to Yes-No questions. Its main fea- tures are 1) a discourse-plan-based approach to implicature, 2) a reversible architecture for gen- eration and interpretation, 3) a hybrid reasoning model that employs both plan inference and log- ical inference, and 4) use of stimulus conditions to model a speaker's motivation for providing ap- propriate, unrequested information. The model handles a wider range of types of indirect answers than previous computational models and has sev- eral significant advantages. 1. INTRODUCTION Imagine a discourse context for (1) in which R's use of just (ld) is intended to convey a No, i.e., that R is not going shopping tonight. (By con- vention, square brackets indicate that the enclosed text was not explicitly stated.) The part of R's re- sponse consisting of (ld) - (le) is what we call an indirect answer to a Yes-No question, and if (lc) had been uttered, (lc) would have been called a direct answer. l.a. Q: I need a ride to the mall. b. Are you going shopping tonight? c. R: [no] d. My car's not running. e. The rear axle is broken. According to one study of spoken English [Stenstrhm, 1984], 13 percent of responses to Yes- No questions were indirect answers. Thus, the ability to interpret indirect answers is required for robust dialogue systems. Furthermore, there are good reasons for generating indirect answers in- stead of just yes, no, or I don't know. First, they may provide information which is needed to avoid misleading the questioner [Hirschberg, 1985]. Sec- ond, they contribute to an efficient dialogue by anticipating follow-up questions. Third, they may be used for social reasons, as in (1). This paper provides a computational model for the interpretation and generation of indirect answers to Yes-No questions in English. More pre- cisely, by a Yes-No question we mean one or more utterances used as a request by Q (the questioner) that R (the responder) convey R's evaluation of the truth of a proposition p. An indirect answer implicitly conveys via one or more utterances R's evaluation of the truth of the questioned proposi- tion p, i.e. that p is true, that p is false, that there is some truth to p, that p may be true, or that p may be false. Our model presupposes that Q's question has been understood by R as intended by Q, that Q's request was appropriate, and that Q and R are engaged in a cooperative goal-directed dialogue. The interpretation and generation com- ponents of the model have been implemented in Common Lisp on a Sun SPARCstation. The model employs an agent's pragmatic knowledge of how language typically is used to answer …

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