Transcript nlpClass.ppt

Referring Expressions:
Definition
Referring expressions are words or phrases,
the semantic interpretation of which is a
discourse entity (also called referent)
Discourse entities are semantic objects and they
can have multiple syntactic realizations within a text
Discourse entities live in the domain D, where a
text is interpreted
Referring Expressions: Example
A pretty woman entered the restaurant.
She sat at the table next to mine and only
then I recognized her. This was Amy
Garcia, my next door neighbor from 10
years ago. The woman has totally
changed! Amy was at the time shy…
Pronouns vs. Full NP
A pretty woman entered the restaurant.
She sat at the table next to mine and only
then I recognized her. This was Amy
Garcia, my next door neighbor from 10
years ago. The woman has totally
changed! Amy was at the time shy…
Definite vs. Indefinite NPs
A pretty woman entered the restaurant.
She sat at the table next to mine and only
then I recognized her. This was Amy
Garcia, my next door neighbor from 10
years ago. The woman has totally
changed! Amy was at the time shy…
Common Noun vs. Proper Noun
A pretty woman entered the restaurant.
She sat at the table next to mine and only
then I recognized her. This was Amy
Garcia, my next door neighbor from 10
years ago. The woman has totally
changed! Amy was at the time shy…
Modified vs. Bare head NP
A pretty woman entered the restaurant.
She sat at the table next to mine and only
then I recognized her. This was Amy
Garcia, my next door neighbor from 10
years ago. The woman has totally
changed! Amy was at the time shy…
Premodified vs. postmodified
A pretty woman entered the restaurant.
She sat at the table next to mine and only
then I recognized her. This was Amy
Garcia, my next door neighbor from 10
years ago. The woman has totally
changed! Amy was at the time shy…
More NP types
Inferrables
He bought a used car. The engine is rather
noisy.\
Discontinuous sets
John has known Bill for many years now.
They often go hiking together.
A more intriguing coloring…
A pretty woman entered the restaurant.
She sat at the table next to mine and only
then I recognized her. This was Amy
Garcia, my next door neighbor from 10
years ago. The woman has totally
changed! Amy was at the time shy…
Referring Expressions:
Definition
Referring expressions are words or phrases,
the semantic interpretation of which is a
discourse entity (also called referent)
Discourse entities are semantic objects and they
can have multiple syntactic realizations within a text
Discourse entities live in the domain D, where a
text is interpreted
Referring expressions and
discourse referents
Centering theory
(Gro 1995) examines interactions
between local coherence and the choice
of referring expressions
A pretty woman entered the restaurant.
She sat at the table next to mine…
A woman entered the restaurant. They like
icecream.
Crash course #1: Centering
theory. Motivation
(Gro 1995) examines interactions
between local coherence and the choice
of referring expressions
Pronouns and definite descriptions are not
equivalent with respect to their effect on
coherence
They make different inference demands
on the hearer or reader.
Crash course #1: Centering
theory. Definitions
The centers of an utterance are discourse
entities serving to link the utterance to other
utterances
Forward looking centers – a ranked list
A backward looking center
Centers are semantic objects, not words,
phrases, or syntactic forms but they are
realized by such in the utterance
Anaphora resolution
Finding in a text all the referring
expressions that have one and the
same denotation
Pronominal anaphora resolution
Anaphora resolution between named
entities
Full noun phrase anaphora resolution
Pronominal anaphora
resolution
Rule-based vs statistical
(Ken 1996), (Lap 1994) vs (Ge 1998)
Performed on full syntactic parse vs on
shallow syntactic parse
(Lap 1994), (Ge 1998) vs (Ken 1996)
Type of text used for the evaluation
(Lap 1994) computer manual texts (86%
accuracy)
(Ge 1998) WSJ articles (83% accuracy)
(Ken 1996) different genres (75% accuracy)
Continued:
Generic vs specific reference
1. The Vice-President of the United States is
also President of the Senate.
2. Historically, he is the President’s key man in
negotiations with Congress
3a. He is required to be 35 years old.
3b. As Ambassador to China, he handled many
tricky negotiations, so he is well prepared for
the job