Computational Linguistics
Introduction
NL Dialogue Systems
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References
• Jurafsky & Martin Ch 19.
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What is Dialogue
• A special kind of discourse
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–
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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…
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What Makes
Dialogue Different?
• Turn Taking
• Grounding
• Implicature
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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.
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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
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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.
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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.
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What Makes
Dialogue Different?
• Turn Taking
• Grounding
• Implicature
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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)
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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?
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What Makes
Dialogue Different?
• Turn Taking
• Grounding
• Implicature
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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 tha t communication to take place.
• Implicature is based on a series of heuristics called
Maxims.
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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.
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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
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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
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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
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Plan Based Theory
of 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.
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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
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Helping Game
• Parameters: Helpee, Helper, Task
• Parameter Specs:
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–
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Helper, Helpee are persons
Helpee wants: helpee perform task
Helpee unable
Helpee permitted
Helper willing to help helpee
Helper able to help helpee
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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
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Helping Game
• I can’t get RUNOFF to work. Can you help
me?
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–
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(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.
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Dialogue Act Markup in
Several Layers (DAMSL)
• Tagging scheme developed by Allen
and Core (1997).
• Codes various levels of dialogue
information
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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
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Forward Looking
STATEMENT
INFO REQUEST
CHECK
INFLUENCE ON ADDRESSEE
OPEN OPTION
ACTION DIRECTIVE
INFLUENCE ON SPEAKER
OFFER
COMMIT
CONVENTIONAL
OPENING
CLOSING
THANKING
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Backward Looking
AGREEMENT
ACCEPT
ACCEPT PART
MAYBE
REJECT PART
REJECT
HOLD
ANSWER
UNDERSTANDING
SIGNAL NON-UNDERSTANDING
SIGNAL UNDERSTANDING
ACK
REPEAT REPHRASE
COMPLETION
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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.
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