Discourse Annotation: Discourse Connectives and Discourse Relations



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Discourse Annotation: Discourse Connectives and Discourse Relations

  • Aravind Joshi and Rashmi Prasad
  • University of Pennsylvania
  • Bonnie Webber
  • University of Edinburgh
  • COLING/ACL 2006 Tutorial
  • Sydney, July 16, 2006

Outline

  • PART I
  • PART II
    • Presentation of PDTB
    • Experiments with PDTB
    • Demo
    • Final Discussion and Questions

Introduction

  • Overall Motivation
    • Richly annotated discourse corpora can facilitate theoretical advances
    • as well as contribute to language technology.
  • Specific Goals
    • Discuss issues related to describing and annotating discourse relations.
    • Describe briefly some specific approaches, which involve reasonably large corpora, highlighting the similarities and differences and how this shapes the resulting annotations.
    • Describe in detail the predominantly lexicalized approach to discourse relation annotation in the Penn Discourse Treebank (PDTB) – partly released in April 2006, final release, April 2007– and illustrate some of its uses.
    •  Encourage you to provide feedback and USE the PDTB!

What is a discourse relation?

  • The meaning and coherence of a discourse results partly from how its constituents relate to each other.
    • Reference relations
    • Discourse relations
  • Informational discourse relations convey relations that hold in the subject matter.
  • Intentional discourse relations specify how intended discourse effects relate to each other.
  • [Moore & Pollack, 1992] argue that discourse analysis requires both types.
  • This tutorial focuses on the former – informational or semantic relations (e.g, CONTRAST, CAUSE, CONDITIONAL, TEMPORAL, etc.) between abstract entities of appropriate sorts (e.g., facts, beliefs, eventualities, etc.), commonly called Abstract Objects (AOs) [Asher, 1993].
  • Reference Relations
  • Discourse Coherence
  • Discourse Relations
  • Informational
  • Intentional

Why Discourse Relations?

  • Discourse relations provide a level of description that is
    • theoretically interesting, linking sentences (clauses) and discourse;
    • identifiable more or less reliably on a sufficiently large scale;
    • capable of supporting a level of inference potentially relevant to many NLP applications.

How are Discourse Relations declared?

  • Broadly, there are two ways of specifying discourse relations:
  • Abstract specification
    • Relations between two given Abstract Objects are always inferred, and declared by choosing from a pre-defined set of abstract categories.
    • Lexical elements can serve as partial, ambiguous evidence for inference.
    • Lexically grounded
    • Relations can be grounded in lexical elements.
    • Where lexical elements are absent, relations may be inferred.

Where are Discourse Relations declared?

  • Similarly, there are two types of triggers for discourse relations considered by researchers:
  • Structure
    • Discourse relations hold primarily between adjacent components with respect to some notion of structure.
    • Lexical Elements and Structure
    • Lexically-triggered discourse relations can relate the Abstract Object interpretations of non-adjacent as well as adjacent components.
    • Discourse relations can be triggered by structure underlying adjacency, i.e., between adjacent components unrelated by lexical elements.

Triggering Discourse Relations

  • Lexical Elements
    • Cohesion in Discourse (Halliday & Hasan)
  • Structure
    • Rhetorical Structure Theory (Mann & Thompson)
    • Linguistic Discourse Model (Polanyi and colleagues)
    • Discourse GraphBank (Wolf & Gibson)
  • Lexical Elements and Structure
    • Discourse Lexicalized TAG (Webber, Joshi, Stone, Knott)
  • Different triggers encourage different annotation schemes.

Halliday and Hasan (1976)

  • H&H associate discourse relations with conjunctive elements:
    • Coordinating and subordinating conjunctions
    • Conjunctive adjuncts (aka discourse adjuncts), including
      • Adverbs such as but, so, next, accordingly, actually, instead, etc.
      • Prepositional phrases (PPs) such as as a result, in addition, etc.
      • PPs with that or other referential item such as in addition to that, in spite of that, in that case, etc.
  • Each such element conveys a cohesive relation between

Halliday and Hasan (1976)

  • H&H use presupposition to mean that a discourse element cannot
  • be effectively decoded except by recourse to another element
  • On a level site you can provide a cross pitch to the entire slab by raising one side of the form, but for a 20-foot-wide drive this results in an awkward 5-inch slant. Instead, make the drive higher at the center.
  • Here instead cannot be effectively decoded without reference to
    • the presupposed predication: raising one side of the form
  • Instead of raising one side of the form, make the drive higher at the center.
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