Centering: A Framework for Modelling the Local Coherence of Discourse, (1995)

Our original paper (Grosz, Joshi, and Weinstein, 1983) on centering claimed that certain entities mentioned in an utterance were more central than others and that this property imposed constraints on a speaker's use of di erent types of referring expressions.Centering was proposed as a model that accounted for this phenomenon.We argued that the coherence of discourse was a ected by the compatibility between centering properties of an utterance and choice of referring expression.Subsequently, we revised and expanded the ideas presented therein.We de ned various centering constructs and proposed two centering rules in terms of these constructs.A draft manuscript describing this elaborated centering framework and presenting some initial theoretical claims has been in wide circulation since 1986.This draft (Grosz, Joshi, and Weinstein 1986, hereafter, gjw86) has led to a number of papers by others on this topic and has been extensively cited, but has never been published. 1e have been urged to publish the more detailed description of the centering framework and theory proposed in gjw86 so that an o cial version would be archivally available.The task of completing and revising this draft became more daunting as time passed and more and more papers appeared on centering.Many of these papers proposed extensions to or revisions of the theory and attempted to answer questions posed in gjw86.It has become ever more clear that it would be useful to have a \de nitive" statement of the original motivations for centering, the basic de nitions underlying the centering framework, and the original theoretical claims.This paper attempts to meet that need.To accomplish this goal, we have chosen to remove descriptions of many open research questions posed in gjw86 as well as solutions that were only partially developed.We have also greatly shortened the discussion of criteria for and constraints on a possible semantic theory as a foundation for this work. IntroductionThis paper presents an initial attempt to develop a theory that relates focus of attention, choice of referring expression, and perceived coherence of utterances within a discourse segment.The research described here is a further development of several strands of previous research.It ts within a larger e ort to provide an overall theory of discourse structure and meaning.In this section we describe the larger research context of this work and then brie y discuss the previous work that led to it.Centering ts within the theory of discourse structure developed by Grosz and Sidner (1986), henceforth, G&S.G&S distinguish among three components of discourse structure: a linguistic structure, an intentional structure, and an attentional state.At the level of linguistic structure, discourses divide into constituent discourse segments; an embedding relationship may hold between two segments.The intentional structure comprises intentions and relations among them.The intentions provide the basic rationale for the discourse, and the 1 Early drafts of gjw86 were in circulation from 1983.Some citations to other work have dates between 1983 and 1986.This work utilized these earlier drafts.