Coherence in Text and Dialogue

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Coherence in Text and Dialogue
Read J M Chapters 18.2, 18.3, 19
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Why is Coherence a Computational Issue?

• Anaphora resolution
• Question answering
• Text extraction
• Text summarization
• Discourse
• Generation

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Question Answering
John arrived at the station later than hed
hoped. He rushed to the ticket booth, then ran
to the platform. He got there just before the
conductor closed the doors. Did John get on the
train? Did John have enough money for the
ticket? Or a news wire example
http//www.csi.uottawa.ca/tanka/QA/sample.html
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Text Extraction
The alphas have a long-standing hatred of the
betas. Their leaders have decided that the time
has come to launch an attack. They are
considering the Thanksgiving weekend, but thats
long ways away. They know theyll have to count
on the fact that they are much better shots than
the betas are.
attack (status ltplanned, imminent, active,
completedgt) (attacker ) (attackee ) (locati
on ) (mode-of-attack ) (time-of-attack )
(credit-claimer )
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Text Summarization
Generating long summaries http//www1.cs.columbi
a.edu/nlp/newsblaster/ Suppose Google
(http//channels.netscape.com/ns/search/default.js
p) returned a summary of a page, not just the
first line domestic robots
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Discourse
What we dont want http//www.dcs.shef.ac.uk/wa
lker/Seinf.mpg What we do want I want to see
The Matrix tonight. It isnt playing anywhere in
town.
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Two Kinds of Knowledge

• Task/domain knowledge
• John offered to go stop by Bills house to pick
  up the report. He didnt have a key but the door
  was unlocked.
• Linguistic/social conventions that govern the way
  we use language
• Local linguistic clues
• John went to the mall but he didnt
  buy anything.
• John went to the mall so he didnt buy
  anything.
• Conventions
• Do you know what time it is?
• Can we come up with a single mechanism for
  representing and reasoning with all of these
  things?

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Task/Domain Knowledge - Scripts
Scripts or frames represent facts about the world
as we know it Example a train-taking
script Scene 1 (arrival) S arrives at
station Scene 2 (ticket purchase) S goes to
ticket window S tells C destination and
class C tells S the price S hands
over money C hands over ticket Scene 3
(boarding) S goes to platform S gets
on train P closes doors
train pulls away Scene 4
travelling etc.
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Task/Domain Knowledge Pre and Post Conditions

• Actions are especially important, particularly in
  interactive dialogue systems. Actions can be
  represented as
• Preconditions
• Postconditions
• Body (sequence of subactions)
• The first two may be able to be represented in
  FOPC. Sometimes the latter is too, or in a
  separate action language. But we may need a
  higher order system.

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Pre and Post Conditions May Involve Beliefs
Do you know what time it is? (Action (Tell, P,
R, A) P tells R A (precondition Know(P,
A) ? Contact(P, R)) (postcondition Know(R, A)
or maybe Know (R, Believe(P,
A))) Know(Tim, time(now, 200)) or Know(Tim
Believe (I, time(now, 200)))
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Linguistic Cues
John went to the mall but he didnt buy
anything. John went to the mall so he didnt go
to the movie. John went to the mall and he went
to the movie. John went to the mall after he went
to the movie. John went to the mall so that he
could go to the movie. John went to the mall even
though he didnt have any money.
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The Structure of Text Relations
The pieces have to hang together, typically in
some tree like structure that represents
relations among the pieces. Some
relations Result John forgot to set his alarm.
So he missed the exam. Explanation John missed
the exam. Hed forgotten to set his
alarm. Parallel/contrast John always brings ham
and cheese. Mary always brings peanut
butter. Elaboration John went to the Friday
night dance. He brought Mary and arrived in a
white limousine. Sequence The police arrested a
tall man for the burglary. They brought him to
the station and read him his rights. Then they
locked him up until morning.
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The Structure of Text Hanging Together
The police are searching for a tall white man.
They canvassed the neighborhood and interviewed
everyone they could find. Then they examined
several security cameras in the area. They think
the robbery was caught on at least one of them.
They are also requesting cell phone records at
the time of the robbery. They are reasonably
certain that they will be able to find their man.
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The Structure of Dialogue Typed vs. Spoken

• In addition to all of the issues we must confront
  with typed dialogues, spoken dialogue management
  must also consider
• Conventions for interruptions and turn taking.
• The need for grounding to confirm success over a
  noisy channel
• False starts
• Ungrammaticality
• Whens the next um or any cheap flights to
  Boston?
• Lets see. Theres one tomorrow at 800.

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The Structure of Dialogue Speech Acts
Talking (or writing) is just one kind of action
that we can take when we want to achieve a goal.
So we should analyze each utterance of a dialogue
just as we would analyze any other action. Some
utterances have an effect just by virtue of being
uttered I name this ship the Titanic. I second
that motion. I bet you five dollars that it will
snow. I hereby announce my candidacy for governor.
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Speech Acts Three Levels
But most utterances are actions because of the
effect they have on their listeners. We can
analyze utterances on three levels Locutionary
act the utterance of some sentence with some
particular linguistic meaning. Illocutionary act
the act of asking or answering or telling or
ordering promising or whatever. Perlocutionary
act the production of some specific effect on
the addressee as a result of the act.
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Speech Acts An Example
Im freezing. Locutionary force DCL(?e time(e,
now) ? cold(e) ? AE(e, speaker)) Illocutionary
force IMP(?e close(e) ? AE(e, window) ? Agent(e,
you) Perlocutionary force closed(window)
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Speech Acts
There are several main classes of speech acts
(illocutionary forces) Assertives/statements
(commits the speaker to S being the
case) Directives (asking, ordering, requesting,
inviting, advising, begging) Commissives (commits
the speaker to some future action) Expressives
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Indirect Speech Acts
Utterances in which the locutionary force and the
illocutionary force are different. Im
freezing. Do you know what time it is? ? Please
tell me the time.
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Planning Speech Acts

• Sequences of utterances require the same kind of
  planning as do sequences of any other actions.
• Planning to generate utterances
• Inferring plans in understanding utterances

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Conversational Implicature

• Grices maxims
• The Maxim of Quantity
• Be as informative as required.
• Dont be more so.
• The Maxim of Quality
• Do not way what you believe to be false.
• Do not say that for which you lack sufficient
  evidence.
• Maxim of relevance Be relevant
• Maxim of manner
• Avoid obscurity of expression
• Avoid ambiguity
• Be brief.
• Be orderly.

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Grices Maxims at Work
For understanding Grices maxims support a
kind of reasoning called implicature, a form of
defeasible inference. By defeasible we mean that
later information can undo the inference. For
example John is in either New York or Paris. I
know which but Im not going to tell you.
Contrast with semantic deductions John
stopped smoking, although he never started. For
generation Grices maxims suggest a generation
strategy that will seem natural and helpful to
human interactors. In both cases, we require a
model of what is required, true, and relevant.
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Conversational Implicature

• Other maxims
• Dont say negative things about others.
• Dont say things that will hurt someones
  feelings.
• Dont use language that is inappropriate to the
  context unless you want to offend.
• Dont reveal things that are more intimate than
  the other person also reveals.
• Etc.

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Examples

1. Do you have any money on you?
2. This volume is well-bound, and free of
   typographical errors.
3. This sure is a great neighborhood.
4. A Im out of gas. B Theres a gas station
   around the corner.
5. A Joe doesn't seem to have a girl-friend these
   days. B He's been going to Dallas a lot lately.
6. A When did you get home last night? B I was
   in bed by midnight.
7. A Lets go to the movies tonight. B I have to
   study for an exam.
8. I need to get to Chicago by noon.
9. A Do you like my new hairstyle. B Its
   interesting.

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Interpretation as Reasoning
A Do you know what time it is? B reasons as
follows A is asking me about what I know.
There must be some reason he wants to know what I
know. My knowing P is a precondition to my being
able to tell him. A is trying to establish the
preconditions to my being able to tell him P.
So what he really wants is for me to tell him P.
I can just do that.
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Scalar Implicature

1. A How many people will fit in your car? B 5
2. Tie and jacket required.
3. No overnight parking.
4. No stopping or standing.
5. No pipe smoking.
6. No stovetop or broiler.
7. Free HBO.
8. No sandals or flipflops.
9. A Have you finished your paper yet? B I
   havent even got a topic yet.

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Presuppositions
In the interest of brevity, we often leave out
many of the assertions that we assume to be true
when we formulate an utterance. In cooperative
discourse, a listener who believes that a
presuppostion is not true should say so A When
did you graduate from college?B I never
went. A Whens the next Delta flight to
Chicago?B Delta doesnt fly to Chicago, or
There arent any more today. A Whats the
monthly fee for long distance service?B There
isnt a fixed monthly fee, or Which level of
service do you want? or We dont offer long
distance service. A Whos the king of France?