Discourse Deixis: Reference to Discourse Segments

DISCOURSE DEIXIS: REFERENCE TO DISCOURSE SEGMENTS Bonnie Lynn Webber Department of Computer & Information Science University of Pennsylvania Philadelphia PA 19104-6389 ABSTRACT Computational approaches to discourse understanding have a two-part goal: (1) to identify those aspects of discourse understanding that require process-based accounts, andS(2) to characterize the processes and data structures they involve. To date, in the area of reference, process-hased ac.omnts have been developed for subsequent reference via anaphoric pronouns and reference via definite descriptors. In this paper, I propose and argue for a process-based account of subsequent reference via deiedc expressions. A significant feature of this account is that it attributes distinct mental reality to units of text often called discourse segments, a reality that is distinct from that of the entities deem therein. 1. INTRODUCTION There seem to be at least two constructs that most current theories of discourse understanding have adopted in at least some form. The In'st is the discourse entity, first introduced by Lauri Karmunen in 1976 (under the name "discourse referent") [9] and employed (under various other names) by many researchers, including myself [18]. The other is the discourse segment. Discourse entities provide these theories with a uniform way of explaining what it is that noun phrases (NP) and pronouns in a discourse refer to. Some NPs evoke a new discourse entity in the listener's evolving model of the discourse (which I have called simply a discourse model), others refer to ones that are already there. Such entities may correspond to something in the outside world, but they do not have to. To avoid confusion with a sense of "referring in the outside world", I will use the terms referm here, meaning "refer in a model", and referentm, for the entity in the model picked out by the linguistic expression. The basic features of a discourse entity are that (a) it is a constant within the current discourse model and that Co) one can attribute to it, inter alia, properties and relationships with other entities. (It is for this reason that Bill Woods once called them "conceptual coat hooks".) In some theories, different parts of the discourse model (often called spaces) may represent diffeaent modalities, including hypothetical contexts, quantified contexts, the belief contexts of different agents, etc. Depending on what space is currently being described, the same NP or pronoun may evoke and/or referm to very different discourse entities. The other common construct is the discourse segment. While discourse segmentation is generally taken to be a chunking of a linguistic text into sequences of related clauses or sentences, James Allen notes: ... there is little consensus on what the segments of a particular discourse should be ~ how segmentation could be accomplished. One reason for this lack of consensus is that there is no precise definition of what a segment is beyond the intuition that certain sentences naturally group together [[1], p. 398-9] What is taken to unify a segment is different in different theories: fox example, among computational linguists, Grosz & Sidner …

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