Curs 10: Veins Theory Discourse structure and coherence Dan Cristea Selecţie de sliduri

On cohesion

Types of references evocative references -evocative resolution processes: - an anaphor may be resolved to a referent that is not linearly the closest, but only hierarchically the closest - based on associations (pattern matching on morpho-semantic features) - fast - give fluency to the text

Types of references - post-evocative resolution processes: - are inferential processes developed in memory, - computationally and cognitively slow (compel to more inference load), - require more powerful referencing means (like proper nouns), - are less frequent. post-evocative references

Domain of evocative accessibility (DEA) dea(u) = pref(u, vein(u)) Remind! The vein expression of a terminal node (discourse unit): the sequence of units that are required to understand just that unit, in the context of the whole discourse. (simplified)

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

From vein expressions V=1 2 3 V=(1 2) 3 V=3 4 V=3 5

... to Domains of Evocative Accessibility V=3 5 V=1 2 3 V=3 4 DEAs V=1 2 3

The reason why she can refer Mary but not 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. antithesis 1414 4 2 elaboration V=1 2 4

The reason why we recuperate with difficulty the antecedent of it 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313 circumstance 21 background V=2 3

… while here the reference is immediate 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313 2 background 3 1 circumstance 123 V=1 2 3

Experiment 1: evocative vs post- evocative references SourceNo. of units Total no. of refs On the veins Outside the veins English %8.30% French %0.90% Romanian %4.50% Total %4.40%

The 4.4% exceptions decreasing evoking power Type of REVT pragmatic56.30% proper nouns22.70% common nouns16.00% pronouns5.00%

Experiment 2: potential to establish correct co-reference links Compare Linear-k and Discourse-VT-k models: –For each k, each re, and each model M (Linear or VT) p(M-k,re,DEA k ) = p(M-k,Corpus) =  re  Corpus p(M-k,re,DEA k ) 1, re can be resolved to antecedents in DEA k 0, otherwise. {

Potentials

Experiment 3: the effort required to find antecedents Compare Linear-k and Discourse-VT-k models: –For each k, each re, and each model M (Linear or VT) e(M-k,re,DEA k ) = e(M-k,Corpus) =  re  Corpus e(M-k,re,DEA k ) d<k, the distance between re and the closest antecedent in DEA k k, if no such antecedent exists. {

Effort: an example Michael D. Casey Genetic Therapy Inc. Mr. Casey Genetic Therapy Inc. Mr. Casey the smaller company Johnson & Johnson M. James Barett chairman its president its J&J Mr. Casey J&J Mr. Barett CEO Michael D. Casey, a top Johnson&Johnson manager, moved to Genetic Therapy Inc., a small biotechnology concern here, 2. to become its president and chief operating officer. 3. Mr. Casey, 46 years old, was president of J&J's McNeil Pharmaceutical subsidiary, 4. which was merged with another J&J unit, Ortho Pharmaceutical Corp., this year in a cost-cutting move. 5. Mr. Casey succeeds M. James Barrett, 50, as president of Genetic Therapy. 6. Mr. Barrett remains chief executive officer 7. and becomes chairman. 8. Mr. Casey said 9. he made the move to the smaller company.

Efforts

The account of VT on coherence Veins give a natural way to generalize Centering from local to global

Centering Rule 2: transitions C b (u) = C b (u-1) C b (u)  C b (u-1) C b (u) = C p (u) C b (u)  C p (u) CONTINUINGSMOOTH SHIFT RETAININGABRUPT SHIFT CON > RET > SSH > ASH

V=1 3 5 V= V=1 3 5 V= Vein expressions give „lines of argumentation“ 1. John sold his bicycle 3. He obtained a good price for it, 5. Therefore he decided to use the money to go on a trip. 1. John sold his bicycle 2. although Bill would have wanted it 3. He obtained a good price for it, 4. which Bill could not have afforded 5. Therefore he decided to use the money to go on a trip.

V=1 3 5 V= V=1 3 5 V= Lines of argumentation 2. although Bill would have wanted it. 1. John sold his bicycle 2. although Bill would have wanted it 3. He obtained a good price for it, 5. Therefore he decided to use the money to go on a trip.

V=1 3 5 V= V=1 3 5 V= Lines of argumentation 3. He obtained a good price for it, 1. John sold his bicycle 3. He obtained a good price for it, 5. Therefore he decided to use the money to go on a trip.

V=1 3 5 V= V=1 3 5 V= Lines of argumentation 4. which Bill could not have afforded. 1. John sold his bicycle 3. He obtained a good price for it, 4. which Bill could not have afforded 5. Therefore he decided to use the money to go on a trip.

V=1 3 5 V= V=1 3 5 V= Lines of argumentation 5. Therefore he decided to use the money to go on a trip. 1. John sold his bicycle 3. He obtained a good price for it, 5. Therefore he decided to use the money to go on a trip.

Computation of longest argumentation lines (al) uV(u)V(u)dea(u)al

Evaluating the coherence of a discourse A smoothness score: –CONTINUING = 4 –RETAINING = 3 –SMOOTH SHIFT =2 –ABRUPT SHIFT = 1 –NO Cb = 0 A global smoothness score: summing up the score of all units

The second conjecture (on coherence) The global smoothness score of a discourse when computed following VT is at least as high as the score computed following CT. But segments, as considered by Centering, typically are developed along veins. When passing segments frontiers, in a linear reading, transitions are usually abrupt. Therefore, what we claim here is that long- distance transitions, as computed along veins, are systematically smoother than accidental transitions at segment boundaries.

Transitions and scores on a linear adjacency metric J = [John], b = [John's bicycle], B = [Bill], p = [price], m = [the money], t = [a trip]) CfJ, bB, bJ, p, bp, BJ, m, t CbJbbp- TransASHRETSSHNo Cb Score1320 Global6/4 = 1.5

Transitions and scores on a hierarchical adjacency metric 12 Cf J, bB, b Cb Jb Trans ASH Score 1 Global 134 J, bJ, p, bp, B JJp CONSSH J, bJ, p, bJ, m, t JJJ CON 4 11/4=2.75

Verifying the second conjecture SourceNo. of transitions CT scoreAverage CT score per transition VT scoreAverage VT score per transition English French Romanian Total

VT references Cristea,D.; Ide,N.; Romary,L. (1998): Veins Theory. An Approach to Global Cohesion and Coherence. In Proceedings of Coling/ACL ‘98, Montreal Cristea,D., Ide,N., Marcu,D., Tablan, M.-V. (2000): Discourse Structure and Co-Reference: An Empirical Study, In Proceedings of The 18th International Conference on Computational Linguistics COLING'2000, LuxembourgDiscourse Structure and Co-Reference: An Empirical Study Ide,N., Cristea,D. (2000): A Hierarchical Account of Referential Accessibility. In Proceedings of The 38th Annual Meeting of the Association for Computational Linguistics, ACL'2000, Hong KongA Hierarchical Account of Referential Accessibility Sereţan,V., Cristea,D. (2002): The use of referential constrains in structuring discourse. In Proceedings of The Third International Conference on Language Resources and Evaluation, LREC-2002, Las Palmas Cristea, D. (2005): Motivations and Implications of Veins Theory, in B.Sharp (Ed.). Natural Language Understanding and Cognitive Science, Proceedings of the 2nd International Workshop on Natural Language Understanding and Cognitive Scienc3, NLUCS 2005, in conjunction with ICEIS 2005, Miami, U.S.A., May 2005, INSTICC Press