ITRI - 00 - 17 Can text structure be incompatible with rhetorical structure ?

Scott and Souza (1990) have posed the problem of how a rhetorical structure (in which propositions are linked by rhetorical relations, but not yet arranged in a linear order) can be realized by a text structure (in which propositions are ordered and linked up by appropriate discourse connectives). Almost all work on this problem assumes, implicitly or explicitly, that this mapping is governed by a constraint on compatibility of structure. We show how this constraint can be stated precisely, and present some counterexamples which seem acceptable even though they violate compatibility. The examples are based on a phenomenon we call extraposition, in which complex embedded constituents of a rhetorical structure are extracted and realized separately.