The Multifaceted Organization Of Discourse

The organization of discourse is multifaceted. Theories that take a single perspective on discourse structure, examining for example only goal satisfaction or textual coherence or ignoring the context in which a text was generated, will fail to identify the full functional significance of the content and organization of text. The task of generating coherent text to meet some communicative intentions requires consideration of a number of constraints on content and organization that manifest in different ways in the end-product. Therefore the task of analyzing a text with respect to its coherence and intended functionality requires factoring distinct influences on the organization of the text itself. Diverse Accounts of Coherence Various accounts of discourse coherence have been offered in the literature, each with their own merits and limitations. For example, Grosz & Sidner [1986] defined a coherent discourse to be one in which a single discourse purpose is "shared bffy all the participants and when each utterance of the discourse contributes to achieving this purpose." Grosz and Sidner provided a clear account of certain aspects of the hierarchical and prerequisite structure of discourse. However they did not address the variety of communicative roles that sibling text segments can play with respect to each other. Intersegmental coherence is the concern of rhetorical structure theory (KST), whose proponents have stated (in various forms, and most directly by Hovy [1988]) that a coherent text is one in which each contiguous segment of text is related by a rhetorical relation. This claim is concisely stated, easy to understand and apply, and intuitively appealing. However it is deficient in being too weak in explanatory power and too strong in its conditions for coherence. It is too weak because the rhetorical relations themselves were developed by identifying relationships between contiguous segments of text in a corpus of texts considered to be coherent. Because of this circularity, the rhetorical characterization of coherence does not account for the sources of coherence or say why the text is coherent: the rhetorical relations are merely descriptive of coherent text. The claim is too strong because coherence does not necessarily require rhetorical relations between every contiguous segment of a text. The ordering of a text can be arbitrary at points. There is unlikely to be a well motivated rhetorical relation between those segments whose contiguity is arbitrary. This problem has shown up in text generation: Moore ~ Paris [1991] encountered certain difficulties …