Discourse Structure

Discourse Segments

• Discourse are divided into segments
  • Within a segment, recency is usable for interpreting anaphora
  • The clauses within a segment refer to one time and place or a simple progression of time and place.
  • A fixed set of speakers and hearers participate with a segment.
  • A fixed set of background assumptions is relevant.
• Segments may be contained in others
• Segments function to
  • Define the context for the interpretation of referring expressions: the referent can only be found with the current segment or its ancestors
  • Facilitate the identification of the relation between a new sentence and previous discourse
• Relations between segments and subsegments
  • Digression
  • Dominance with respect to discourse purpose
    • Event description: subsegment describes part of event
    • Argument: subsegment provides evidence for claim
    • Instructions: subsegment tells how to perform subtask
• Example (digression)

  1a A: You've got the back off, right?
  1b B: Yep.
  1c A: Well, look on the right side, way in the back.
  1d    You'll see what looks like a little light bulb.
  1e    That's the thing you need to remove.
  2a    By the way, did you remember to buy some cheese on the way
        home?
  2b B: Oops.  I forgot.
  2c A: Well, I won't be able to make that lasagna.
  2d B: Too bad.
  1f A: OK, have you got it out?
  

• Example (dominance)

  1a There are a number of reasons to be concerned about sending troops
     to Bosnia.
  2a First, American lives may be lost.
  2b Despite assurances, there appear to be people over there who are
     hostile to the NATO forces.
  3a Second, there is no clear exit strategy.
  3b It's possible that we could get bogged down there like we did in
     Vietnam.
  4a Third, it could be argued that what happens in the Balkans is not
     in the self-interest of the United States.
  4b What would we gain even if peace were maintained?
  5  Despite these three reasons, and others as well, it appears that
     sending troops is the least of a whole range of possible evils.
  

Discourse Segmentation

• Detecting discourse segment boundaries
  • Cue phrases
    • Indicating semantic relations: and, because, but, so, then
    • Indicating discourse structure: anyway, by the way, first, next, OK, bye
  • Referring expressions which only make sense if a segment boundary has occurred, e.g,, three reasons in 5 above
  • Tense/aspect change
    John and Mary went out for dinner on Friday. They had met the week before at a wedding for Mary's sister. They hit it off well because they discovered that they both hated weddings.
• The attentional stack
  • Attentional stack contains segments (really discourse states), the current one at the top.
  • Each new sentence
    • May be part of the current segment: the segment at the top of the stack is updated
    • May begin a subsegment of the current segment: the new segment is pushed onto the stack
    • May begin a subsegment of a parent (or other ancestor) of the current segment: the segment at the top is popped and the new segment pushed onto the stack
    • May contine the parent (or other ancestor) of the current segment: the segment at the top is popped and the parent segment updated

[L645 Syllabus]