Evaluating Centering for Information Ordering Using Corpora M.Sc. Seminar: Discourse Coherence Theories and Modeling Jonathan Poitz Department of Computational Linguistics, Saarland University May 13th, 2013 Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 1 / 35
Motivation It shows a beautiful sunset. Most of my vacations I spend on Malta. I took this picture on the west coast of the island last year. Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 2 / 35
Motivation Most of my vacations I spend on Malta. I took this picture on the west coast of the island last year. It shows a beautiful sunset. Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 2 / 35
Papers to be presented 1 Evaluating Centering for Information Ordering Using Corpora (K ARAMANIS , P OESIO , M ELLISH , O BERLANDER 2008) 2 Specifying the Parameters of Centering Theory: a Corpus-Based Evaluation using Text from Application-Oriented Domains (P OESIO et al. 2000) Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 3 / 35
Overview 1 Centering Theory The Theory Principles of Centering Parameters of Centering 2 Application on Information Ordering Motivation The Metrics Experimental Evaluation 3 Test Data Results Conclusion Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 4 / 35
A possible approach - Centering Theory Questions to be answered 1 How appropriate is the Centering Theory for Information Ordering? 2 Which aspects of it are most useful? Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 5 / 35
Centering Theory The Theory What is Centering? • Developed by Barbaba Grosz, Candy Sidner & Aravind Joshi (1986, 1995) • Goal was to offer a new approach for anaphora resolution • Two different data structures for each utterance: • CF(U) – Forward looking center holding all Discourse Entities (DE) of utterance n with the preferred center CP(U) defined as its first item • CB(U) – Backward looking center defined as highest ranked element of CF(U n − 1) that also occurs in CF(U n ) Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 6 / 35
Centering Theory The Theory An Example Example Most of my vacations I spend on Malta. CF: {vacations, I, Malta} CB: {n.a.} Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 7 / 35
Centering Theory The Theory An Example Example Most of my vacations I spend on Malta. CF: {vacations, I, Malta} CB: {n.a.} I took this picture last year. CF: {I, picture, last year} CB: {I} Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 7 / 35
Centering Theory The Theory An Example Example Most of my vacations I spend on Malta. CF: {vacations, I, Malta} CB: {n.a.} I took this picture last year. CF: {I, picture, last year} CB: {I} It shows a beautiful sunset. CF: {picture, sunset} CB: {picture} Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 7 / 35
Centering Theory The Theory The transitions Comparing the forward and backward looking centers of an utterance several transitions were defined by Brennan, Friedman & Pollard in 1987. • Continue • Retain • Smooth-Shift • Rough-Shift • NOCB (Kibble & Power 2000) Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 8 / 35
Centering Theory The Theory An example 1 This cake is amazing and I am very 1 CB(U) : n.a. hungry! 2 CB(U) : cake 2 A friend prepared it yesterday. 3 CB(U) : friend 3 He is a good cook. 4 CB(U) : friend 4 He also sometimes prepares delicious 5 CB(U) : pasta pasta. 6 CB(U) : n.a. 5 Unfortunately I’m allergic to pasta. 6 Green elephants eat breakfast. Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 9 / 35
Centering Theory The Theory An example 1 This cake is amazing and I am very 1 CB(U) : n.a. hungry! 2 CB(U) : cake 2 A friend prepared it yesterday. 3 CB(U) : friend 3 He is a good cook. 4 CB(U) : friend 4 He also sometimes prepares delicious 5 CB(U) : pasta pasta. 6 CB(U) : n.a. 5 Unfortunately I’m allergic to pasta. Continue CB(U n ) = CB(U n − 1) and CB(U n ) = CP(U n ) 6 Green elephants eat breakfast. Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 9 / 35
Centering Theory The Theory An example 1 This cake is amazing and I am very 1 CB(U) : n.a. hungry! 2 CB(U) : cake 2 A friend prepared it yesterday. 3 CB(U) : friend 3 He is a good cook. 4 CB(U) : friend Retain 4 He also sometimes prepares delicious 5 CB(U) : pasta CB(U n ) = CB(U n − 1) or CB(U n − 1) = undef. pasta. 6 CB(U) : n.a. and CB(U n ) � = CP(U n ) 5 Unfortunately I’m allergic to pasta. 6 Green elephants eat breakfast. Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 9 / 35
Centering Theory The Theory An example 1 This cake is amazing and I am very 1 CB(U) : n.a. hungry! 2 CB(U) : cake 2 A friend prepared it yesterday. 3 CB(U) : friend 3 He is a good cook. 4 CB(U) : friend 4 He also sometimes prepares delicious 5 CB(U) : pasta pasta. Smooth Shift 6 CB(U) : n.a. CB(U n ) � = CB(U n − 1) and CB(U n ) = CP(U n ) 5 Unfortunately I’m allergic to pasta. 6 Green elephants eat breakfast. Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 9 / 35
Centering Theory The Theory An example 1 This cake is amazing and I am very 1 CB(U) : n.a. hungry! 2 CB(U) : cake 2 A friend prepared it yesterday. 3 CB(U) : friend 3 He is a good cook. 4 CB(U) : friend 4 He also sometimes prepares delicious 5 CB(U) : pasta pasta. 6 CB(U) : n.a. 5 Unfortunately I’m allergic to pasta. 6 Green elephants eat breakfast. Rough Shift CB(U n ) � = CB(U n − 1) and CB(U n ) � = CP(U n ) Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 9 / 35
Centering Theory The Theory An example 1 This cake is amazing and I am very 1 CB(U) : n.a. hungry! 2 CB(U) : cake 2 A friend prepared it yesterday. 3 CB(U) : friend 3 He is a good cook. 4 CB(U) : friend 4 He also sometimes prepares delicious 5 CB(U) : pasta pasta. 6 CB(U) : n.a. 5 Unfortunately I’m allergic to pasta. 6 Green elephants eat breakfast. NOCB CB = n.a. Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 9 / 35
Centering Theory The Theory Rules and Constraints • Constraint 1: All utterances of a segment except for the first have exactly one CB. • Rule 1: If any element of U n − 1 is realized by a pronoun in U n , the CB(U n ) is too. • Rule 2: Sequence preferences are Continue > Retain > Smooth Shift > Rough Shift Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 10 / 35
Centering Theory The Theory Rules and Constraints • Constraint 1: All utterances of a segment except for the first have exactly one CB. • Rule 1: If any element of U n − 1 is realized by a pronoun in U n , the CB(U n ) is too. • Rule 2: Sequence preferences are Continue > Retain > Smooth Shift > Rough Shift Example for rule 1 Peter is in a bad mood. He visited his friend John. He didn’t like Peter’s visit. Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 10 / 35
Centering Theory The Theory Rules and Constraints • Constraint 1: All utterances of a segment except for the first have exactly one CB. • Rule 1: If any element of U n − 1 is realized by a pronoun in U n , the CB(U n ) is too. • Rule 2: Sequence preferences are Continue > Retain > Smooth Shift > Rough Shift Example for rule 1 Example for rule 2 Peter is in a bad mood. Peter likes to play the drums. He visited his friend John. He and Paul are friends of Mary. He didn’t like Peter’s visit. She doesn’t like what he eats. Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 10 / 35
Centering Theory Principles of Centering Details of Centering I • Centering Theory was developed and refined by several researcher groups • Therefore no single version exists, but lots of different parameters and principles were introduced to suit the individual purposes • Cheapness: (Strube & Hahn 1999) defined as CB(U n ) = CP(U n − 1) • Meant to improve anaphora resolution, but also used by the authors for calculating quality of ordering • Rule 2 was modified to always favor sequences that satisfy Cheapness Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 11 / 35
Centering Theory Principles of Centering Details of Centering II • Continuity and NOCB: CF(U n ) should contain at least one member of CF(U n − 1) resp. NOCB accounting for the case of Continuity violation • Coherence: subsumes Continue and Retain transitions and is satisfied if backward looking center stays the same • Salience: in turn combines Continue and Smooth Shift and therefore cases where the backward looking center is also the most highly ranked element Jonathan Poitz (CoLi Saarland) Evaluating Centering for Information Ordering May 13th, 2013 12 / 35
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