Curs 6: Teorii ale discursului: AST şi RST

1. Curs 6: Teorii ale discursului: AST şi RST Dan Cristea Selecţie de slide-uri prezentate în tutoriale (RANLP-03, Borovits, Sept. 2003; ICON-04, Hyderabad, Dec. 2004) şi conferinţe

2. Content I. Introduction • What is discourse? Text versus discourse. Coherence and cohesion. II. Theories • attentional state theory • rhetorical structure theory

3. What is discourse? Longman: 1. a serious speech or piece or writing on a particular subject: Professor Grant delivered a long discourse on aspects of moral theology. 2. serious conversation between people: You can’t expect meaningful discourse when you two disagree so violently. 3. the language used in particular kinds of speech or writing: scientific discourse.

4. What is discourse? Longman: 1. a serious speech or piece or writing on a particular subject: Professor Grant delivered a long discourse on aspects of moral theology. 2. serious conversation between people: You can’t expect meaningful discourse when you two disagree so violently. 3. the language used in particular kinds of speech or writing: scientific discourse.

5. From Garcia Marquez Text versus discourse Syntactically – a discourse is more than a single sentence.

6. Text versus discourse A text is not a discourse! But it becomes a discourse the very moment it is read or heard by a human... or a machine.

7. real time 1 2 discourse time 1 2 story time 2 1 800 920 1000 1030 Time and discourse Discourse has a dynamic nature Time axes

8. Cohesion and coherence A text manifests cohesion when its parts closely correlate. A text is coherent when it makes sense, with respect to an accepted setting, real or virtual.

9. knowledge about the language knowledge about the world knowledge about the situation knowledge about the author text setting Interpretation of discourse discourse interpretation

10. Discourse phenomena: interruptions and flash-backs E: Now attach the pull rope to the top of the engine. By the way, did you buy gasoline today? A: Yes. I got some when I bought the new lawnmower wheel. I forgot to take the gas with me, so I bought a new one. E: Did it cost much? A: No, and we could use another anyway to keep with the tractor. E: OK, how far have you got? Did you get it attached? from (Allen, 1987)

11. Discourse phenomena: pop-overs E: Now attach the pull rope to the top of the engine. By the way, did you buy gasoline today? A: Yes. I got some when I bought the new lawnmower wheel. I forgot to take the gas with me, so I bought a new one. E: Did it cost much? A: No, and we could use another anyway to keep with the tractor. E: OK, how far have you got? Did you get it attached? from (Allen, 1987)

12. Discourse phenomena: pop-overs E: Now attach the pull rope to the top of the engine. By the way, did you buy gasoline today? A: Yes. I got some when I bought the new lawnmower wheel. I forgot to take the gas with me, so I bought a new one. E: Did it cost much? A: No, and we could use another anyway to keep with the tractor. E: OK, how far have you got? Did you get it attached? from (Allen, 1987)

13. Discourse phenomena: inference load and pronoun use Why is it that some discourses seem more difficult to understand than others? Why do we use the pronouns and other anaphoric means the way we do? localising the setting cohesion is lower coherence is lower

14. Discourse theories? Sub-domain of Computational Linguistics: searching for the intrinsic laws of the discourse and for models making possible an automated analysis, representation and generation of the discourse.

15. II. Discourse theories • atentional state theory • rhetorical structure theory • centering theory • veins theory

16. Attentional state theory(AST) (Barbara Grosz & Candence Sidner, 1987) Models the linguistic structure of the discourse Gives an account on intentions and how they are combined Explains the shift of attention during discourse interpretation Explains interruptions and flash-backs Puts in evidence a dynamic domain of referentiality 3 components

17. AST: 1st component • a linguistic structure: • more sentences are aggregated in the same segment • segments display a recursive structure

18. AST: 2nd component • an intentional structure: • a segment communicates an intention, it has a goal to accomplish in the reader; • the goals of the component segments contribute to the realisation of the goal of the overall segment; • two type of relations between segment goals: dominance and satisfaction-precedence

19. A A AA AAA AAB AA AB AC AAB ABA ABB AB ABA ABB AAA AC AST: 2nd component Relations: dominance DSP A dominates DSP AA: the intention associated with DSP AA contributes to the satisfaction of the intention associated with DSP A

20. A AA AB AC AAA AAB ABA ABB AST: 2nd component Relations: satisfaction-precedence DSP AA satisfaction-precedes DSP AB: DSP AA must be satisfied before DSP AB

21. A SA AST: 3rd component • an attentional state • to each segment corresponds a space of entities under focus • these spaces have the dynamics of a stack A AA AB AC AAA AAB ABA ABB

22. AA SAA AST: 3rd component • an attentional state • to each segment corresponds a space of entities under focus • these spaces have the dynamics of a stack A A AB AC SA AAA AAB ABA ABB

23. SAAA AAA AST: 3rd component • an attentional state • to each segment corresponds a space of entities under focus • these spaces have the dynamics of a stack A A AA AB AC SAA SA AAB ABA ABB

24. SAAB AAB AST: 3rd component • an attentional state • to each segment corresponds a space of entities under focus • these spaces have the dynamics of a stack A A AA AB AC SAA SA AAA ABA ABB

25. AST: 3rd component • an attentional state • to each segment corresponds a space of entities under focus • these spaces have the dynamics of a stack A A AA AB AC SAB SA AAA AAB ABA ABB

26. AST: 3rd component • an attentional state • to each segment corresponds a space of entities under focus • these spaces have the dynamics of a stack A A SABA AA AB AC SAB SA AAA AAB ABA ABB

27. AST: 3rd component • an attentional state • to each segment corresponds a space of entities under focus • these spaces have the dynamics of a stack A A SABB AA AB AC SAB SA AAA AAB ABA ABB

28. AST: 3rd component • an attentional state • to each segment corresponds a space of entities under focus • these spaces have the dynamics of a stack A A AA AB AC SAC SA AAA AAB ABA ABB

29. AST: 3rd component • an attentional state • to each segment corresponds a space of entities under focus • these spaces have the dynamics of a stack A A AA AB AC SA AAA AAB ABA ABB

30. AST: 3rd component • an attentional state • to each segment corresponds a space of entities under focus • these spaces have the dynamics of a stack A A AA AB AC AAA AAB ABA ABB

31. AST: 3rd component • an attentional state • accessibility modeled by the top-down access in the stack A SABB AA AB AC SAB SA AAA AAB ABA ABB

32. AST explains interruptions E: Now attach the pull rope to the top of the engine. By the way, did you buy gasoline today? A: Yes. I got some when I bought the new lawnmower wheel. I forgot to take the gas with me, so I bought a new one. E: Did it cost much? A: No, and we could use another anyway to keep with the tractor. E: OK, how far have you got? Did you get it attached? from (Allen, 1987) An interruption is a discourse segment whose DSP is not dominated nor satisfaction-preceded by the DSP of the immediately proceeding segment.

33. … … … AST: interruptions By the way, did you buy gasoline today? A: Yes. I got some when I bought the new lawnmower wheel. E: Now attach the pull rope to the top of the engine. I forgot to take the gas with me, so I bought a new one. E: Did it cost much? A: No, and we could use another anyway to keep with the tractor. E: OK, how far have you got? Did you get it attached? …

34. AST explains flashbacks Whoops I forgot about ABC. I need an individual concept for the company ABC. … Sinit … SABC … SBillOK. Now how do I say that Bill is... SFB SBillNow back to Bill. How do I say that Bill is an employee of ABC? From (Grosz and Sidner, 1987) A flashback is a particular kind of interruption whose DSP satisfaction-precedes the interrupted segment or a segment that dominates the interrupted segment.

35. AST: flashbacks Sinit … SABC … SBillOK. Now how do I say that Bill is... SFBWhoops I forgot about ABC. I need an individual concept for the company ABC. … SBillNow back to Bill. How do I say that Bill is an employee of ABC? From (Grosz and Sidner, 1987) A flashback is a particular kind of interruption whose DSP satisfaction-precedes the interrupted segment or a segment that dominates the interrupted segment. Sinit SFB SABC SBill SBill SFB SFB SFB SABC SBill SBill Sinit Sinit Sinit flashback starts flashback ends

36. AST doesn‘t accommodate left satellites a. Jack and Sue went to buy a new lawn mower b. since their old one was stolen. c. Sue had seen the men who took it and d. had chased them down the street, e. but they'd driven away in a truck. f. After looking in the store g. they realized they couldn't afford a new one. h. By the way, Jack lost his job last month i. so he's been short of cash recently. j. He has been looking for a new one, k. but so far hasn't had any luck. l. Anyway, they finally found a used one at a garage sale. From (Allen, 1993)

37. AST doesn‘t accommodate left satellites a. Jack and Sue went to buy a new lawn mower b. since their old one was stolen. f. After looking in the store g. they realized they couldn't afford a new one. l. Anyway, they finally found a used one at a garage sale. c. Sue had seen the men who took it and d. had chased them down the street, e. but they'd driven away in a truck. h. By the way, Jack lost his job last month i. so he's been short of cash recently. j. He has been looking for a new one, k. but so far hasn't had any luck.

38. a. Jack and Sue went to buy a new lawn mower a. Jack and Sue went to buy a new lawn mower b. since their old one was stolen. a a,b Attentional state stack

39. a. Jack and Sue went to buy a new lawn mower b. since their old one was stolen. c. Sue had seen the men who took it and d. had chased them down the street, e. but they'd driven away in a truck. c,d,e a,b Attentional state stack

40. a. Jack and Sue went to buy a new lawn mower b. since their old one was stolen. f. After looking in the store g. they realized they couldn't afford a new one. c. Sue had seen the men who took it and d. had chased them down the street, e. but they'd driven away in a truck. a,b,f,g Attentional state stack

41. a. Jack and Sue went to buy a new lawn mower b. since their old one was stolen. f. After looking in the store g. they realized they couldn't afford a new one. h. By the way, Jack lost his job last month i. so he's been short of cash recently. j. He has been looking for a new one, k. but so far hasn't had any luck. c. Sue had seen the men who took it and d. had chased them down the street, e. but they'd driven away in a truck. h,i,j,k a,b,f,g Attentional state stack

42. a. Jack and Sue went to buy a new lawn mower b. since their old one was stolen. f. After looking in the store g. they realized they couldn't afford a new one. l. Anyway, they finally found a used one at a garage sale. h. By the way, Jack lost his job last month i. so he's been short of cash recently. j. He has been looking for a new one, k. but so far hasn't had any luck. c. Sue had seen the men who took it and d. had chased them down the street, e. but they'd driven away in a truck. a,b,f,g,l Attentional state stack

43. Problem:a finer granularity • Jack and Sue went to buy a new lawn mower • g. they realized they couldn't afford a new one. • l. Anyway, they finally found a used one at a garage sale. b. since their old one was stolen. c, d, e f. After looking in the store h, i, j, k

44. Problem c,d,e b b f a a a a a, g

45. AST: pluses • Discourse structure: • a proposal for discourse structure • stack behavior models hierarchical relationships among text segments • Reference: accounted for by accessibility in the stack • Explains interruptions • Explains flash-backs

46. AST: minuses Stack mechanism fails for certain dominant/dominated segment configurations when granularity is sufficiently fine Does not accommodate left satellites The stack model is impurified with an artificial border (in treating interruptions) Do we have an additional memory from where states have to be restored (in treating flashbacks)?

47. Rhetorical structure theory (William Mann and Sandra Thompson, 1987) Basics • text span: un uninterrupted linear interval of text • relation: holds between two or more non-overlapping spans • arguments of relations are of a nuclear type and a satellite type • a nucleus is more important than a satellite (deletion and substitution tests) • relations: hypotactic (one nucleus + satellites) and paratactic (all nuclear) • scheme: integrates by a relation two or more text spans (like grammar rules) • RST analysis are trees • they reflect a judge interpretation (therefore could be subjective)

48. relation text span: satellite text span: nucleus relation text span: nucleus text span: nucleus RST schemes

49. relation2 relation1 relation2 relation1 relation1 relation2 RST schemes: equivalences

50. relation relation relation relation relation relation RST schemes: equivalences