Discourse and Dialogue 6.1.1 beyond Sentence Interpretation 6.1.2 Interpretation and Generation in Context 6.2 Discourse Modeling 6.2.1 Overview: Discourse and Dialogue 6.2.2 Discourse Representation Theory Mechanisms for Handling Key Linguistic Phenomena: of the Predominant

The problems addressed in discourse research aim to answer two general kinds of questions: (1) what information is contained in extended sequences of utterances that goes beyond the meaning of the individual utterances themselves? (2) how does the context in which an utterance is used aaect the meaning of the individual utterances, or parts of them? Computational work in discourse has focused on two diierent types of discourse: extended texts and dialogues, both spoken and written. Although there are clear overlaps between these|dialogues contain text-like sequences spoken by a single individual and texts may contain dialogues|the current state of the art leads research to focus on diierent questions for each. In addition, application opportunities and needs are diierent. Work on text is of direct relevance to document analysis and retrieval applications whereas work on dialogue is of import for human-computer interfaces regardless of the modality of interaction. A good sense of the current state of research in text interpretation can be gained from reading the papers on text interpretation in a Text and dialogue have, however, two signiicant commonalities. First, a major result of early work in discourse was the determination that discourses divide into discourse segments much like sentences divide into phrases. Utterances group into segments, with 227 228 Chapter 6: Discourse and Dialogue the meaning of a segment encompassing more than the meaning of the individual parts. Diierent theories vary on the factors they consider central to explaining this segmentation; a review of the alternatives can be found in a previous survey (Grosz, Pollack, et al., 1989) (hereafter, Discourse Survey). 1 However, many of the implications for language processing are shared. For example, segment boundaries need to be detected; recent work suggests there are intonational indicators of these boundaries in spoken language (e.g., Grosz & Hirschberg, 1992 and the references cited in this paper) and can be used to improve speech synthesis (e.g., Davis & Hirschberg, 1988). Second, discourse research on the interpretation of referring expressions, including pronouns and deenite descriptions (e.g., le petit chat, das gr une Buch), and the event reference aspect of verb phrase interpretation (e.g., the relationship between the buying and arriving events in the sequence John went to Mary's house; he had bought owers at her favorite orist's also is relevant to both text and dialogue. Work on these problems before 1990 is described in Discourse Survey. The major lines of research on …