Focusing and Reference Resolution in PUNDIT

This paper describes the use of focusing in the PUNDIT text processing system. Focusing, as discussed by [Sidner1979] (as well as the closely related concept of centering, as discussed by [Grosz1983] ), provides a powerful tool for pronoun resolution. However, its range of application is actually much more general, in that it can be used for several problems in reference resolution. Specifically, in the PUNDIT system, focusing is used for one-anaphora, elided noun phrases, and certain types of definite and indefinite noun phrases, in addition to its use for pronouns. Another important feature in the PUNDIT reference resolution system is that the focusing algorithm is based on syntactic constituents, rather than on thematic roles, as in Sidner's system. This feature is based on considerations arising from the extension of focusing to cover one-anaphora. These considerations make syntactic focusing a more accurate predictor of the interpretation of one-anaphoric noun phrases without decreasing the accuracy for definite pronouns.