G22.2590 - Natural Language Processing - Spring 2005 Prof. Grishman

Lecture 12 Outline

April 25, 2003

Asgn 8 and pattern learning:  people were able to get many of the examples to work (except those with a name recognition error), but the process of developing all these patterns is time consuming.  Many extraction systems now learn patterns (or probabilistic extraction models) from annotated text, or in some cases even from unannotated text.

Discourse.  Until now we considered the structure and meaning of sentences in isolation.  We now turn to issues primarily connected with multi-sentence text -- discourse.

Reference Resolution (J&M 18.1)


Types of referring expressions


Resolving pronoun reference

Resolving other referring expressions

Anaphora resolution in Jet

Using anaphora resolution for extraction:  an example

In many cases, we want to be able to retrieve an argument from context when it is not part of the immediate syntactic structure.  A simple way of doing this is to generate a zero anaphor (an ngroup constituent not spanning any text) and then let reference resolution map it to an entity.  We have created a version of the AppointPatterns which uses this method to collect organization names and, in some cases, people names.

Discourse Analysis:  Analyzing Text Coherence  (J&M 18.2)

Why are we interested in analyzing the structure of a discourse beyond the sentence level? How to analyze text coherence?