Among the set of schemata specified by Rhetorical Structure Theory is a pattern known variously as the request schema, satellite tie, multisatellite nucleus, or convergence. The essential feature of this schema is that it permits multiple satellites to attach to a single nucleus. Although the schema has long been considered fundamental to RST, it has never been subjected to detailed evaluation. This paper provides such an assessment. Close examination shows that it results in structures that are ambiguous, disjoint, incomplete, and sometimes incoherent. Fortunately, however, further examination shows it to be unnecessary. This paper describes the difficulties with convergences and presents methods for refactoring them as explicit specifications of text structure. The study shows that convergences can be more clearly rendered not as flat relational conjunctions, but rather as organized expressions of cumulative rhetorical moves, wherein each move asserts an identifiable structural integrity and the expressions conform to specifiable scoping rules.

Although diagrams are fundamental to Rhetorical Structure Theory, their interpretation has received little in-depth exploration. This paper presents an algorithmic approach to accessing the meaning of these diagrams. Three algorithms are presented. The first of these, called reenactment, recreates the abstract process whereby structures are created, following the dynamic of coherence development, starting from simple relational propositions, and combing these to form complex expressions which are in turn integrated to define the comprehensive discourse organization. The second algorithm, called composition, implements Marcu’s strong nuclearity assumption. It uses a simple inference mechanism to demonstrate the reducibility of complex structures to simple relational propositions. The third algorithm, called compress, picks up where Marcu’s assumption leaves off, providing a generalized fully scalable procedure for progressive reduction of relational propositions to their simplest accessible forms. These inferred reductions may then be recycled to produce RST diagrams of abridged texts. The algorithms described here are useful in positioning computational descriptions of rhetorical structures as discursive processes, allowing researchers to go beyond static diagrams and look into their formative and interpretative significance.

The relational status of Attribution in Rhetorical Structure Theory has been a matter of ongoing debate. Although several researchers have weighed in on the topic, and although numerous studies have relied upon attributional structures for their analyses, nothing approaching consensus has emerged. This paper identifies three basic issues that must be resolved to determine the relational status of attributions. These are identified as the Discourse Units Issue, the Nuclearity Issue, and the Relation Identification Issue. These three issues are analyzed from the perspective of classical RST. A finding of this analysis is that the nuclearity and the relational identification of attribution structures are shown to depend on the writer’s intended effect, such that attributional relations cannot be considered as a single relation, but rather as attributional instances of other RST relations.

This paper describes how Rhetorical Structure Theory (RST) and relational propositions can be used to define a method for rendering and analyzing texts as expressions in propositional logic. Relational propositions, the implicit assertions that correspond to RST relations, are defined using standard logical operators and rules of inference. The resulting logical forms are used to construct logical expressions that map to RST tree structures. The resulting expressions show that inference is pervasive within coherent texts. To support reasoning over these expressions, a set of rules for negation is defined. The logical forms and their negation rules can be used to examine the flow of reasoning and the effects of incoherence. Because there is a correspondence between logical coherence and the functional relationships of RST, an RST analysis that cannot pass the test of logic is indicative either of a problematic analysis or of an incoherent text. The result is a method for analyzing the logic implicit within discursive reasoning.