Centering: A Framework for Modeling the Local Coherence of Discourse

7 Applications of the rules

1. Why is “He has been acting quite odd. He called up Mike yesterday. John wanted to meet him urgently.” incoherent?
   It violates Rule 1: the \(C_b\) (John) is realized by a name while another entity (Mike) is a pronoun, so the only reading is a second person named John, and even that is odd.
   • Grosz et al., 1995, Centering (Computational Linguistics), §7
2. Annotate the transitions in: “John has been having a lot of trouble arranging his vacation. He cannot find anyone to take over his responsibilities. He called up Mike yesterday to work out a plan. Mike has annoyed him a lot recently. He called John at 5 AM on Friday last week.”

   utterance	\(C_b\)	\(C_f\)	transition
   He called up Mike…	John	John, Mike	continue
   Mike has annoyed him…	John	Mike, John	retain
   He called John…	Mike	Mike, John	shift

   Rule 1 holds throughout.
   • Grosz et al., 1995, Centering (Computational Linguistics), §7
3. When is it fine to realize the \(C_b\) with a full noun phrase instead of a pronoun?
   When no pronouns are used and the description conveys extra information: “My dog is getting quite obstreperous. I took him to the vet. The mangy old beast always hates these visits.” The hearer infers the \(C_b\) is unchanged and that the description holds of it.
   • Grosz et al., 1995, Centering (Computational Linguistics), §7
4. How does centering handle “The house appeared to have been burgled. The door was ajar. The furniture was in disarray.”?
   The house is the \(C_b\) of the later utterances though only realized, not directly realized: the door and the furniture express functional relations to it (an implicitly focused entity). The door ranks above the house in \(C_f\), yet the segment stays “about” the house.
   • Grosz et al., 1995, Centering (Computational Linguistics), §7