• coreference/co-reference - occurs when two or more expressions in a text refer to the same person or thing; they have the same referent (e.g. Bill said he would come; the proper noun Bill and the pronoun he refer to the same person, namely to Bill)

Coreference Types

Indefinite Noun Phrase

  • I saw an Acura Integra today
  • Some Acura Integras were being unloaded

Definite Noun Phrase

  • Tom loves the Acura Integra

Epithet Noun Phrase

  • Tom used his credit card to much, the poor guy bankrupted

Surface Count

  • Lynn has 2 boyfriends, Mark and Kevin
  • She likes the former better

One Anaphora

  • I saw no less than 6 Acuras. Now I want one

Generics

  • I saw no less than 6 Acuras. They are the coolest cars

Inferables

  • I almost bought an Acura today, but a door had a dent and the engine seemed noisy

Syntactic & Semantic Constraints on Coreference

  • John has 3 new Acuras. They are all red (number)
  • You and I have Acuras. We love them (person)
  • John has an Acura. It is attractive (gender)
  • John bought himself a new Acura (himself = John)

Selectional Restrictions

  • John parked his Acura in the garage. He had driven it for hours

selectional restrictions are violated in the case of metaphor

  • John bought a new Acura. It drinks gasoline like you wouldn’t believe

Semantic Constraints

  • John parked his Acura in the garage. It is incredibly messy, with old bike and car parts lying around

Coreference Resolution - Heuristics

Recency

  • John has an Acura. Bill has a Legend. Mary likes to drive it

Grammatical Role

treat entities in the subject position as more salient than those in object position, which in turn are more salient than those mentioned in subsequent positions

  • John went to the Acura dealership with Bill. He bought an Integra

Repeated Mention

  • John needed a car to get to his new job. He decided that he wanted something sporty. Bill went to the Acura with him. He bought an Integra

Verb Semantics

certain verbs place a semantically oriented emphasis on one of their argument positions

  • John telephoned Bill. He lost the pamphlet on Acuras
  • John criticized Bill. He lost the pamphlet on Acuras

Coreference Resolution - Algorithms

  • Lappin & Leas Pronouns Resolution Algorithm