Coherence in Text and Dialogue. Read J & M Chapters 18.2, 18.3, 19. Why is Coherence a Computational Issue?. Anaphora resolution Question answering Text extraction Text summarization Discourse Generation. Question Answering.
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Coherence in Text and Dialogue
Read J & M Chapters 18.2, 18.3, 19
John arrived at the station later than he’d 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
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 that’s long ways away. They know they’ll have to count on the fact that they are much better shots than the betas are.
attack(status <planned, imminent, active, completed>)
Generating long summaries:
Suppose Google (http://channels.netscape.com/ns/search/default.jsp) returned a summary of a page, not just the first line:
What we don’t want:
What we do want:
I want to see The Matrix tonight.
It isn’t playing anywhere in town.
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
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, 2:00)) or Know(Tim Believe (I, time(now, 2:00)))
John went to the mall but he didn’t buy anything.
John went to the mall so he didn’t 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 didn’t have any money.
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. He’d 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.
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.
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.
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.
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)
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)
Utterances in which the locutionary force and the illocutionary force are different.
Do you know what time it is? Please tell me the time.
For understanding: Grice’s 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 I’m not going to tell you.
Contrast with semantic deductions:
* John stopped smoking, although he never started.
For generation: Grice’s 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.
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.
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: When’s the next Delta flight to Chicago?B: Delta doesn’t fly to Chicago, orThere aren’t any more today.
A: What’s the monthly fee for long distance service?B: There isn’t a fixed monthly fee, or Which level of service do you want? orWe don’t offer long distance service.
A: Who’s the king of France?