An Integrated Approach to Reference and Presupposition Resolution

, O @ O O O O O @ O O O O O O O O @ O O O @ O O O O O O O @ O O O O O O O O O O An Integrated Approach to Reference and Presupposition Resolution Robert T. Kasper, Paul C. Davis~ and Craige Roberts Department of Linguistics Ohio State University 222 Oxley Hall 1712 Neil Avenue Columbus, OH 43210" e-mail: (kasper~ pcdavis, croberts}@ling.ohio-state.edu Abstract We describe an approach to resolving definite de- scriptious and pronominal anaphora as subcases of a general strategy for presupposition satisfaction. Generally, a presupposition is satisfied in a context if the context contains a specific type of information and is organized in such a way that this information can be retrieved by the interlocutors. The model of discourse context we develop assumes that dis- course structure is organized around a stack of ques- tions under discussion, which plays a crucial role in narrowing the search for referents and other presup- posed information. The algerithmA for maintaining the discourse structures and retrieving presupposed information are presented and illustrated by several example dialogues in which human users interact with an agent tomake hotel reservatious. I Introduction "Any theory of referring expressions must take into account the discourse context in which they ot~ur. Indeed, previous research has shown that the hier- archical organization of discourse is fundamentally related to the rderence resolution process. In this paper, we show how a highly structured discourse model, in conjunction with a treatment of referring expressions as presuppmitional, enables us to de- velop a common strategy for z~olving a number of reference resolution problems, such as pronominal anaphora and definite descriptions. We also out- line how this approach extends to a larger group of phenomena which we take to be presuppositional,. including domain restriction, ellipsis, and lexically and syntactically triggered presuppositions. All of these constructions are presuppositional in a broad sense, in that their use assumes that certain infor- marion can be retrieved from the discourse context. RecoL, nlzing the structure of the discourse will there- fore play a crucial role in narrowing the search for referents and other presupposed information. We will illustrate our approach with four example human-computer dialogues, shown below. SYS in- dicates the utterances spoken by the computer sys- tem. Example I illustrates a case of pronominal anaphora resolution (it in (8)), in which recowniT.ing the hierarchical structure of the discourse is crucial for identifying the antecedent, which was introduced many utterances earlier. The overall topic of the conversation is the question of where the user can find a hotel for June 15th in New York, and th|8 snper-question both facilitates and constrains the intexpretafion of fl in (8). This example is similar to the well-known examples of long-distance anaphora in task-oriented dialogues described by Grosz (1981). Our approach is consistent with pre- vious research that uses the intentional structure of discourse to determine a set of potential antecedents for pronominal anaphora. The following examples will …

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