discourse martin hassel kth nada royal institute of technology 100 44 stockholm +46-8-790 66 34...
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Discourse
Martin HasselKTH NADA
Royal Institute of Technology100 44 Stockholm+46-8-790 66 34
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2Martin Hassel
What is a discourse?
• The linguistic term for a contextually related group of sentences or utterances
• Basic discourse types• Monologue• Dialogue• HCI turn taking / ”dialogue”
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3Martin Hassel
Cohesion and Coherence
• Cohesion • The bond that ties sentences to one another on a
textual level
• Coherence• The application of cohesion in order to form a
discourse
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4Martin Hassel
Reference Phenomena 1
• Indefinite noun phrases• an apple, some lazy people
• Definite noun phrases• the fastest computer
• Demonstratives• this, that
• One-anaphora
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5Martin Hassel
Reference Phenomena 2
• Inferrables• car engine, door
• Discontinous sets• they, them
• Generics• they
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6Martin Hassel
Referential Constraints
• Agreement• Number• Person and case• Gender
• Syntactic constraints• Selectional restrictions
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7Martin Hassel
Coreferential Expressions
• Coreference• Expressions denoting the same discourse entity corefer
• Anaphors• Refer backwards in the discourse• The referent is called the antecedent
• Cataphors• Refer forwards in the discourse
Although he loved fishing, Paul went skating with Mary.
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8Martin Hassel
Pronouns 1
• A pronoun that emphasizes a person, place, or idea is demonstrative• these, that, this, those
• A pronoun that forms a question in the sentence is interrogative• whom, who, which, what, whose
• Subordinate clauses are introduced by relative pronouns• that, which, whose, whom, who
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9Martin Hassel
Pronouns 2
• Possessive pronouns are used to show ownership over something else.• whose, your, its, their
• A pronoun is personal if it refers to the person speaking. It is also personal if it refers to the person being spoken to or the person being spoken about.• all, another, many, someone, other, neither, anybody
• A person, place, or thing that is not specifically named is refered to by a indefinite pronoun.• I, my, our, yours, you, its, they, their, them
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10Martin Hassel
Pronouns 3
• Seldom refer more than two sentences back• Requires a salient referent as antecedent
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11Martin Hassel
Antecedent Indicators
• Recency• Grammatical role• Parallellism• Repeated mention• Verb semantics
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12Martin Hassel
Text Coherence
• Coherence relations• Result• Explanation• Parallel• Elaboration• Occasion
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13Martin Hassel
Coherence Relations 1
• When S0 is a first sentence and S1 is a second sentence in the same discourse:
• Result• S0 causes or can cause S1
• Explanation• S1 is (or can be) the cause of what is stated in S0
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14Martin Hassel
Coherence Relations 2
• Parallel• Rabbits eat carrots. Cats eat mice.
• Elaboration• Peter bought some food. He bought two bananas and
a dietary fruit drink.
• Occasion• Peter bought some snacks. He ate in front of the TV.
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15Martin Hassel
Discourse Structure
• John went to the bank to deposit his paycheck (S1)• He then took a train to Bill’s car dealership (S2)• He needed to buy a car (S3)• The company he works for now isn’t near any
public tranportation (S4)• He also wanted to talk to Bill about their softball
league (S5)
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16Martin Hassel
A Discourse Tree
S2 (S2 (ee2)2)
Explanation (Explanation (ee2)2)
Occasion (Occasion (ee1;1;ee2)2)
S1 (S1 (ee1)1)
Parallel (Parallel (ee3;3;ee5)5)
S3 (S3 (ee3)3)
S5 (S5 (ee5)5)Explanation (Explanation (ee3)3)
S4 (S4 (ee4)4)
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17Martin Hassel
Inference 1
Rule: If it rains the ground gets wet
Observation: It rains
Conclusion: The ground gets wet
Deduction: rule + observation → conclusion (modus ponens)
Induktion: observation +conclusion → rule (modus tollens)
Abduktion: rule + conclusion - (?!) → obeservation
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18Martin Hassel
Inference 2
• John hid Bill’s car keys. He was drunk.1. John usually does stupid things when drunk
2. Bill often drives when drunk
• Bill was drunk. John hid his car keys.1. Bill tends to ”borrow” cars when drunk
2. Bill often drives his car when drunk
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19Martin Hassel
Background Knowledge
• The problem of encoding inference is usually said to AI-complete
• AI-completeness indicates that the problem requires all of the knowledge – and utilities to utilize it – that humas possess
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20Martin Hassel
Different Levels
• Syntax• Rules for constructing grammatical sentences
• Semantics• Rules for assigning meaning to statements
• Pragmatics• Rules (of thumb) for applying contextual constraints on
the semantics of a statement
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21Martin Hassel
Pragmatics
• The study of meaning contained by utterences in situations (Leech, 1983)
• Relates the content of a clause (semantics) with the content of an utterance of that clause (pragmatics)
• Pragmatic rules often rules of thumb• Dialogues – Cooperative Principles
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22Martin Hassel
Grice’ Cooperative Principle
• Grice' Cooperative Principles (Grice 1975) are a set of conversational principles that have been developed to facilitate conversation.
• These principles are usually, or should be, followed in order to effectivly convey the meaning of an utterance.
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23Martin Hassel
• Quantity– Don’t say more that necessary
• Quality– Do not say anything you do not believe in or have proof
of• Relevance
– A response should be an answer to the question• Form
– Be clear– Avoid ambiguity– Be consice– Be methodical
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24Martin Hassel
Discourse, what for?
• Information Retrieval• Summarization• Pronoun Resolution
…• Natural Language Generation