Discourse Coherence

Abstract

The naive semantic representations in the KT system contain enough information to recover much of the discourse structure of a text. The first part of this chapter describes coherence and segmentation phenomena in text understanding, and defends a set of genre-relative coherence relations. The next part places discourse coherence in an overall theory of grammar and relates coherence theory to the formal semantics of discourse as expressed in Discourse Representation Theory (DRT) (Kamp, 1981, Heim, 1982, Asher, 1987). The broad theory in place, we demonstrate that just the syntax and logical form of the sentences in the discourse do not provide sufficient information to assign coherence. In order to recover the discourse structure of the text, the recipient must often appeal to commonsense knowledge (Lockman and Klappholz, 1980, Hobbs, 1985). Given that syntactic and semantic information alone does not suffice to assign discourse coherence, the next section analyzes the contribution of each level of grammar in parallel to this task. Next we illustrate the parallel use of all levels of grammar in recovering the structure of a text taken from the newspaper. Finally, the processing implications of the parallel model of discourse is explored.