Syntax-Centered and Semantics-Centered Views of Discourse. Can They be Reconciled?

In this paper, we argue that there are two seemingly incompatible perceptions of discourse structure: a semantics-centered view and a syntax-centered view. In the semantics-based view, discourse structure is viewed as a structure that identifies the most important portions of the text and describes how they combine semantically. In the syntax-based view, discourse structure is viewed as an extension of syntax to the discourse level, which essentially links the syntactic trees for the individual sentences into one big tree structure. We will argue that these differences in perception may explain some of the central disagreements in the literature about the nature of discourse structure, in particular whether discourse structure is best viewed as a tree or a general graph. However, the two views are not as incompatible as they may seem at first sight, since the semantic discourse structure can be reinterpreted as a functor-argument structure that is derived from the syntactic tree structure. We describe the ramifications of the two views for the analysis of discourse markers, which are the focus of the discourse annotation in the Penn Discourse Treebank, and show how the syntax-based view can maintain a tree structure even for examples that seem to exhibit non-tree like properties in a semantics-based view