Discourse Martin Hassel KTH NADA Royal Institute of Technology Stockholm

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”

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

4Martin Hassel Reference Phenomena 1 Indefinite noun phrases an apple, some lazy people Definite noun phrases the fastest computer Demonstratives this, that One-anaphora

5Martin Hassel Reference Phenomena 2 Inferrables car  engine, door Discontinous sets they, them Generics they

6Martin Hassel Referential Constraints Agreement Number Person and case Gender Syntactic constraints Selectional restrictions

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.

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

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

10Martin Hassel Pronouns 3 Seldom refer more than two sentences back Requires a salient referent as antecedent

11Martin Hassel Antecedent Indicators Recency Grammatical role Parallellism Repeated mention Verb semantics

12Martin Hassel Text Coherence Coherence relations Result Explanation Parallel Elaboration Occasion

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

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.

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)

16Martin Hassel A Discourse Tree S2 (e2) Explanation (e2) Occasion (e1;e2) S1 (e1) Parallel (e3;e5) S3 (e3) S5 (e5) Explanation (e3) S4 (e4)

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

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

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

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

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

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.

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

24Martin Hassel Discourse, what for? Information Retrieval Summarization Pronoun Resolution … Natural Language Generation