Curs 9: Veins Theory Discourse structure and cohesion

1. Curs 9: Veins Theory Discourse structure and cohesion Dan Cristea Selecţie de sliduri

2. Overview • What do we expect… • Some linguistic motivations • Basics of the Veins Theory (VT) • Cohesion in VT

3. What do we expect from a theory of discourse? • To tell us how is the discourse structured • To make explicit, using this discourse structure, some discourse phenomena: at least cohesion and coherence • To explain interruptions, flashbacks (all from Grosz&Sidner)… • To explain how the structure can be built from the raw text • To be easily put at the base of implementations in different settings

4. Some linguistic motivations

5. Are you comfortable with finding a referent for it in unit 3? 1. With one year before finishing his mandate as president of the company, 2. Mr. W. Ross has begun to bring about its bankruptcy. 3. There were rumors that he has obtained it by fraud.

6. Are you comfortable with finding a referent for it in unit 3? 1. With one year before finishing his mandate as president of the company, 2. Mr. W. Ross has begun to bring about its bankruptcy. *3. There were rumors that he has obtained it by fraud.

7. How about now? 1. Mr. W. Ross has begun to bring about the bankruptcy of his company. 2. with one year before finishing his mandate as president. 3. There were rumors that he has obtained it by fraud.

8. How about now? 1. Mr. W. Ross has begun to bring about the bankruptcy of his company. 2. with one year before finishing his mandate as president. 3. There were rumors that he has obtained it by fraud.

9. How many of you think that she in unit 4 refers John’s mother? 1 John told Mary that he loves her. 2. He has never been married 3. and lived until his 40s with his mother. 4. She, on the contrary, was married twice.

10. Discourse structure modifies the distance between anaphor and antecedent 1 John told Mary that he loves her. 2. He has never been married 3. and lived until his 40s with his mother. 4. She, on the contrary, was married twice. 24 antithesis 2 4

11. Discourse structure modifies the distance between anaphor and antecedent 1 John told Mary that he loves her. 2. He has never been married 3. and lived until his 40s with his mother. 4. She, on the contrary, was married twice. 14 elaboration 24 antithesis 1 2 4

12. A satellite can access a far nucleus… 1 John told Mary that he loves her. 2. He has never been married 3. and lived until his 40s with his mother. 4. She, on the contrary, was married twice. 14 elaboration antithesis 1 elaboration 4 3 2

13. … but not another satellite 1 John told Mary that he loves her. 2. He has never been married 3. and lived until his 40s with his mother. 4. She, on the contrary, was married twice. 14 elaboration antithesis 1 elaboration 4 3 2

14. A nucleus blocks the access between two satellites… 1. With one year before finishing his mandate as president of the company, 2. Mr. W. Ross has begun to bring about its bankruptcy. 3. There were rumors that he has obtained it by fraud. 13 background circumstance 1 2 3

15. … and a satellite can access its nucleus 1. Mr. W. Ross has begun to bring about the bankruptcy of his company. 2. with one year before finishing his mandate as president. 3. There were rumors that he has obtained it by fraud. 13 circumstance background 1 3 2

16. Veins Theory – basics

17. Fundamental assumption in VT (the cohesion claim) • An inter-unit reference is possible only if the two units are in a structural relation one with the other • The nucleus-satellite distinction, as a component of the discourse structure, gives indications on the range of referents to which an anaphor can be resolved

18. relations nuclear labeled units 1 4 2 3 Trees as in RST

19. The definitions of VT: heads • Head expression of a node: the sequence of the most important units within the corresponding span of text: • the head of a terminal node: its label • the head of a non-terminal node: the concatenation of the head expressions of the nuclear daughters • the important units are projected up to the level where the corresponding span is seen as a satellite

20. Veins Vein expression of a node: the sequence of units that are required to understand the span of text covered by the node, in the context of the whole discourse to understand a piece of text in the context of the whole discourse one needs the significant units within the span together with other surrounding units

21. Veins • Vein expressions are computed top-down starting with the root • the vein expression of the root is its head expression H=h V=h

22. V=v V=v Vein expressions • A nuclear node with no satellites to the left V=v

23. V=v H=h Vein expressions • A nuclear node with left satellites V=seq(mark(h), v)

24. V=v H=h Vein expressions • A satellite node on the left V=seq(h, v)

25. V=v H=h Vein expressions • A satellite node on the right V= seq(h, simpl(v))

26. Example of simplification V0=v V1=seq(mark(h1), v) H=h1 H=h2 V= seq(h2, simpl(V1))

27. Example of simplification V0=v V1=seq(mark(h1), v) H=h1 H=h2 V= seq(h2, simpl(seq(mark(h1), v)))

28. Example of simplification V0=v V1=seq(mark(h1), v) H=h1 H=h2 V= seq(h2, simpl(seq(mark(h1), v)))

29. Example of simplification V0=v V1=seq(mark(h1), v) H=h1 H=h2 V= seq(h2, seq(v))

30. Example of simplification V0=v V1=seq(mark(h1), v) H=h1 H=h2 V= seq(h2, seq(v))

31. Example of simplification V0=v V1=seq(mark(h1), v) H=h1 H=h2 V= seq(h2, v)

32. 2 5 4 3 1 Heads and veins H=1 2 H=3 H=3 V=3 V=3 H=5 V=3 5 V=1 2 3 H=3 H=1 V=(1 2) 3 V=1 2 3 H=2 H=4 H=3 V=1 2 3 V=(1 2) 3 V=3 4