May 2006CLINT CS Dialogue1 Computational Linguistics Introduction NL Dialogue Systems

May 2006 CLINT CS Dialogue 1

Computational Linguistics Introduction

NL Dialogue Systems


References

• Jurafsky & Martin Ch 19.


What is Dialogue• A special kind of discourse

– Prose– Argument– Monologue– Dialogue

• Like all discourse shares the following– Anaphora - e.g. pronouns and referents– Coherence

John hid Bill’s car keys. He was drunkJohn hid Bill’s car keys. He likes spinach

• But it also has special features…


What Makes Dialogue Different?

• Turn Taking• Grounding• Implicature


Turn Taking

• Utterances and Turns.– One utterance can take several turns– One turn can include several utterances.

• How do speakers know when is the proper time to contribute their turn?

• Sacks (1974) proposed that turn-taking is rule-governed.


One Utterance, Several Turns

A: yeah yeah the um let me see here we’ve got you on American flight nine thirty eight

C: yepA: leaving on the twentieth of June out of

Orange County John Wayne Airport at 7.30 pm

C: 7.30A: and into uh San Francisco at eight fifty seven


Several Utterances, One Turn

A: Three two three and seven five one. OK and then does he know there is a nonstop that goes from Dulles to San Fransisco? Instead of connection through St Louis.


Turn Taking Rule(Sacks 1974)

• If during this turn the current speaker has selected A as the next speaker then A must speak next

• If the current speaker does not select the next speaker, any other speaker may take the next turn

• If no-one else takes the next turn, the current speaker may take the next turn.





Grounding• Speaker and hearer must constantly establish

common ground. Ways of establishing common ground include:– Continued attention (I am still attending)– Acknowledgement (I understood what you just

said)– Demonstration (I will show you part of what I

understood)• When things go wrong there are ways to

indicate this:– Repair request (I didn’t get it: please repeat)


Grounding Examples

DemonstrationA: OK I’ll take the 5ish flight on the night

before on the 11thB: On the 11th?

Repair RequestA: Why is that?B: Huh?A: Why is that?





Implicature

A: And what day in May did you want to travel?B: I need to be there for a meeting that’s from the 12th to

the 15th.• B’s answer does not actually answer the question.• Somehow the speaker communicates more than is

actually said• Implicature is the mechanism which makes it possible

for that communication to take place.• Implicature is based on a series of heuristics called

Maxims.


Maxim of Relevance• If we assume that B’s answer is relevant, we can

infer a connection.– If speaker has to be at a meeting from 12th to 15th

May then he has to be there by 12th.– If he has to be there by 12th he has to travel on

11th.– Therefore, we infer the answer is 12th May

• The problem with such a mechanism is control of the inference process

• Many other things can be inferred from B’s utterance. • Computation of relevant inferences is hard.


Gricean Maxims• Maxim of Quantity: say exactly enough (no more and

no less)– Maggie ate some of the chocolate.– Implicature: she did not eat all of the chocolate

• Maxim of Quality: be truthful– That will cost the earth– Implicature: that will cost a great deal

• Maxim of Relevance: be relevant• Maxim of Manner: be clear (avoid ambiguity,

obscurity, long windedness)– Are you going to come or aren’t you?– Implicature: the hearer is witholding the information


Dialogue Acts

• An important insight about conversation, originally due to Austin (1962) is that an utterance in a dialogue is a kind of action being performed by the speaker– I name this ship Titanic– I hereby pronounce you man and wife– I bet you he’ll lose


Speech Acts• Assertives

– Suggest, swear, conclude• Directives

– Ask, order, invite, advise, beg• Commissives

– Promise, plan, bet, vow• Expressives

– Thank, apologise, welcome, deplore• Declarations

– Resign, volunteer


Plan Based Theoryof Speech Acts

(Perrault and Cohen 198...)• To satisfy their goals, people plan

speech acts to to affect their listeners’ beliefs and goals.

• Such language use can be modelled by viewing speech acts as operators in a planning system.

• Integration of planning mechanisms for both physical and social actions.


Dialogue GamesLevin and Moore (1976)

• A Dialogue Game is a method of attempting to solve a problem through communicative actions.

• Each game has a set of problems for which it is appropriate

• Certain preconditions must hold beforehand• Exit conditions provide guarantees on the

resulting state.• One of the possible terminal states includes the

solution of the original problem


Helping Game

• Parameters: Helpee, Helper, Task• Parameter Specs:

– Helper, Helpee are persons– Helpee wants: helpee perform task– Helpee unable– Helpee permitted– Helper willing to help helpee– Helper able to help helpee


Helping Game

• Rules– Helpee describes actions already

performed.– Helpee describes unexpected outcome– Helper recommends to Helpee actions

which help Helpee do task.– If Helper is unable to help– Helper initiates Cannot Help Game


Helping Game

• I can’t get RUNOFF to work. Can you help me?– (task is (get RUNOFF to work))– (speaker unable (perform task))– (speaker want (speaker perform task))– (speaker want (hearer help speaker (perform

task)))• These assertions are matched against

preconditions of game which is then activated.


Dialogue Act Markup in Several Layers (DAMSL)

• Tagging scheme developed by Allen and Core (1997).

• Codes various levels of dialogue information


Levels of Dialogue Information

Levels Include• Information Level: semantic content of the

utterance.• Forward Looking Function - how the current

utterance constrains the future beliefs and actions of the participants – c.f. promising

• Backward Looking Function - how the current utterance relates to the previous discourse – c.f. accepting


Forward LookingSTATEMENTINFO REQUEST

CHECKINFLUENCE ON ADDRESSEE

OPEN OPTIONACTION DIRECTIVE

INFLUENCE ON SPEAKEROFFERCOMMIT

CONVENTIONALOPENINGCLOSINGTHANKING


Backward LookingAGREEMENT

ACCEPTACCEPT PARTMAYBEREJECT PARTREJECTHOLD

ANSWERUNDERSTANDING

SIGNAL NON-UNDERSTANDINGSIGNAL UNDERSTANDING

ACKREPEAT REPHRASECOMPLETION



Summary

• Dialogue is a special kind of discourse• For a computer to participate in dialogues it

has to classify the utterances into types.• Utterance classification is non-trivial• Utterance types are like action-types• Participating in a dialogue involves reasoning

about plans made of action-type instances.

Documents

May 2006CLINT CS Dialogue1 Computational Linguistics Introduction NL Dialogue Systems