More or Less Elaborate

The notion of structural scalarity of subordinating relations is introduced and semantic and pragmatic consequences pointed out. A measure for relevance of elaborations, as a special case of subordinating relation, is suggested. Discourse structure and scalarity Theorists (Grosz & Sidner 1986; Mann & Thompson 1988; Asher & Lascarides 2003) agree that coherent discourse is representable by a connected graph: for every vertex in a graph representing a discourse unit, there is a path connecting it to every other vertex in the representation. Moreover, these graphs are usually taken to be hierarchical in that two types of relations hold: coordinating and subordinating. Besides these general agreements, there are stark differences in the assumptions on graph representations. (E.g., only in Rhetorical Structure Theory (RST, (Mann & Thompson 1988)), the edges are assumed to be asymmetric in that they represent relations connecting a satellite to a nucleus.) Recently, it has been suggested to consider the assignment of relations between discourse units not to be an all-or-nothing decision. The difference in accepability of examples like (1) John loves sport. He hates football. (2) John loves sport. But he hates football. (taken from (Asher & Lascarides 2003, 169)) are said to be indicative for a stronger Contrast relation in example (2) as compared to (1). This is a case of what I call qualitative scalarity. Until now, scalarity has always been discussed in the context of co-ordinating discourse relations (like Contrast or Narration); in the present paper, I will shift the view and include sub-ordinating relations, my prime example being Elaboration. Copyright c © 2008, Association for the Advancement of Artificial Intelligence (www.aaai.org). All rights reserved. Structural scalarity Consider the following example, translated from a dutch newspaper1 [According to the police, there was also some work for first aid teams and ambulance personnel.][Six visitors had to be brought to the hospital because they incurred small injuries.][Hurt knees, burns, that sort of things.][Five others could be treated immediately.][Blisters and hyperventilation were at issue.] I suggest to analyse the example as follows: unit 1 is elaborated by unit 2, which in turn is elaborated by unit 3; unit 4 is coordinated to unit 2, and further elaborated by unit 5. For a start, I follow (Asher & Vieu 2005, 595) and adopt the principle Continuing Discourse Patterns (CDP): If R1(α, β) and R2(β, γ), and Subord(R1) and Coord(R2), then R1(α, γ) and Continuation(β, γ) (in addition to R2(β, γ)). From this principle it follows that unit 4, just like unit 2, elaborates unit 1. I now suggest to drop the Continuation relations and generalize CDP to Structural Scalarity: If R1(α, β, n) and R2(β, γ, 0), and Subord(R1) and • either Coord(R2), then R1(α, γ, n) • or Subord(R2), then R1(α, γ, n+ 1) (in addition to R2(β, γ, 0)). In case of a co-ordinating relation between β and γ, the relation to a superordinated unit α is just the same, as stipulated by CDP. The extension I propose captures the intuition from (Grosz & Sidner 1986) that subordinated (purposes of) discourse units serve to achieve the purposes of dominating units: the “inherited” relation R1(α, γ, n+ 1) if Subord(R2) in the above definition is, as I want to put it, a structurally weaker version of R1 as holding between α and β. Structural scalarity is thus a syntactic measure for the distance between a node in a discourse representation and the Source: Algemeen Dagblad 20 Aug 2007, www.ad.nl/rotterdam/stad/article1596957.ece 115 Proceedings of the Twenty-First International FLAIRS Conference (2008)