A Tripartite Plan-Based Model of Dialogue

A TRIPARTITE PLAN-BASED MODEL OF DIALOGUE Lynn Lambert Sandra Carberry Department of Computer and Information Sciences University of Delaware Newark, Delaware 19716, USA Abstract 1 This paper presents a tripartite model of dialogue in which three different kinds of actions are modeled: domain actions, problem-solving actions, and dis- course or communicative actions. We contend that our process model provides a more finely differenti- ated representation of user intentions than previous models; enables the incremental recognition of com- municative actions that cannot be recognized from a single utterance alone; and accounts for implicit acceptance of a communicated proposition. 1 Introduction This paper presents a tripartite model of di- alogue in which intentions are modeled on three levels: the domain level (with domain goals such as traveling by train), the problem-solving level (with plan-construction goals such as instantiating a pa- rameter in a plan), and the discourse level (with communicative goals such as ezpressing surprise). Our process model has three major advantages over previous approaches: 1) it provides a better repre- sentation of user intentions than previous models and allows the nuances of different kinds of goals and processing to be captured at each level; 27 it enables the incremental recognition of commumca- tire goals that cannot be recognized from a single utterance alone; and 3) it differentiates between il- locutionary effects and desired perlocutionary ef- fects, and thus can account for the failure of an inform act to change a heater's beliefs[Per90] ~. 2 Limitations of Current Models of Discourse A number of researchers have contended that a coherent discourse consists of segments that are related to one another through some type of structuring relation[Gri75, MT83] or have used rhetorical relations to generate coherent text[Hov88, MP90]. In addition, some researchers 1 This material is based upon work supported by the Na- tional Science Foundation under Grant No. IRI-8909332. The Government has certain rights in this material. 2We would ilke to thank Kathy McCoy for her comments on various drafts of this paper. have modeled discourse based on the semantic rela- tionship of individual clauses[Po186a] or groups of clauses[Rei78]. But all of the above fail to capture the goal-oriented nature of discourse. Grosz and Sidner[GS86] argue that recognizing the structural relationships among the intentions underlying a dis- course is necessary to identify discourse structure, but they do not provide the details of a compu- tational mechanism for recognizing these relation- ships. To account for the goal-oriented nature of discourse, many researchers have adopted the planning/plan-recognition paradigm[APS0, PA80] in which utterances are viewed as part of a plan for accomplishing a goal and understanding con- sists of recognizing this plan. The most well- developed plan-based model of discourse is that of Litman and AIIen[LA87]. However, their discourse plans conflate problem-solving actions and commu- nicative actions. For example, their Correct-Plan has the flavor of a problem-solving plan that one would pursue in attempting to construct another plan, whereas their Identify-Parameter takes on some of the characteristics of a communicative plan that one would pursue …

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