Representing discourse coherence: A corpus-based analysis

We present a set of discourse structure relations that are easy to code, and develop criteria for an appropriate data structure for representing these relations. Discourse structure here refers to informational relations that hold between sentences in a discourse (cf. Hobbs, 1985). We evaluated whether trees are a descriptively adequate data structure for representing coherence. Trees are widely assumed as a data structure for representing coherence but we found that more powerful data structures are needed: In coherence structures of naturally occurring texts, we found many different kinds of crossed dependencies, as well as many nodes with multiple parents. The claims are supported by statistical results from a database of 135 texts from the Wall Street Journal and the AP Newswire that were hand-annotated with coherence relations, based on the annotation schema presented in this paper.