May 2006CLINT CS Dialogue1 Computational Linguistics Introduction NL Dialogue Systems

May 2006CLINT CS Dialogue2 References Jurafsky & Martin Ch 19.

May 2006CLINT CS Dialogue3 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 drunk John hid Bill’s car keys. He likes spinach But it also has special features…

May 2006CLINT CS Dialogue4 What Makes Dialogue Different? Turn Taking Grounding Implicature

May 2006CLINT CS Dialogue5 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.

May 2006CLINT CS Dialogue6 One Utterance, Several Turns A: yeah yeah the um let me see here we’ve got you on American flight nine thirty eight C: yep A: leaving on the twentieth of June out of Orange County John Wayne Airport at 7.30 pm C: 7.30 A: and into uh San Francisco at eight fifty seven

May 2006CLINT CS Dialogue7 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.

May 2006CLINT CS Dialogue8 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.

May 2006CLINT CS Dialogue9 What Makes Dialogue Different? Turn Taking Grounding Implicature

May 2006CLINT CS Dialogue10 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)

May 2006CLINT CS Dialogue11 Grounding Examples Demonstration A: OK I’ll take the 5ish flight on the night before on the 11th B: On the 11th? Repair Request A: Why is that? B: Huh? A: Why is that?

May 2006CLINT CS Dialogue12 What Makes Dialogue Different? Turn Taking Grounding Implicature

May 2006CLINT CS Dialogue13 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.

May 2006CLINT CS Dialogue14 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.

May 2006CLINT CS Dialogue15 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

May 2006CLINT CS Dialogue16 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

May 2006CLINT CS Dialogue17 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

May 2006CLINT CS Dialogue18 Plan Based Theory of Speech Acts (Perrault and Cohen ) 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.

May 2006CLINT CS Dialogue19 Dialogue Games Levin 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

May 2006CLINT CS Dialogue20 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

May 2006CLINT CS Dialogue21 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

May 2006CLINT CS Dialogue22 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.

May 2006CLINT CS Dialogue23 Dialogue Act Markup in Several Layers (DAMSL) Tagging scheme developed by Allen and Core (1997). Codes various levels of dialogue information

May 2006CLINT CS Dialogue24 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

May 2006CLINT CS Dialogue25 Forward Looking STATEMENT INFO REQUEST CHECK INFLUENCE ON ADDRESSEE OPEN OPTION ACTION DIRECTIVE INFLUENCE ON SPEAKER OFFER COMMIT CONVENTIONAL OPENING CLOSING THANKING

May 2006CLINT CS Dialogue26 Backward Looking AGREEMENT ACCEPT ACCEPT PART MAYBE REJECT PART REJECT HOLD ANSWER UNDERSTANDING SIGNAL NON-UNDERSTANDING SIGNAL UNDERSTANDING ACK REPEAT REPHRASE COMPLETION

May 2006CLINT CS Dialogue27

May 2006CLINT CS Dialogue28 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.