Empirical Study of Predictive Powers od Simple Attachment Schemes for Post-Modifier Prepositional Phrases

This empirical study attempts to find answers to the question of how a natural language (henceforth NL) system could resolve attachment of prepositional phrases (henceforth PPs) by examining naturally occurring PP attachments in typed dialogue. Examination includes testing predictive powers of existing attachment theories against the data. The result of this effort will be an algorithm for interpreting PP attachment. I n t r o d u c t i o n Difficulty in resolving structural ambiguity involving PPs arises because of the great variety of syntactic structures which PPs can modify and the varying distances PPs may be from the constituents with which they are associated. Simple schemes to resolve attachments utilize information drawn from reported tendencies in the human parsing mechanism, such as the preference for PPs to attach to constituents that immediately precede them. It is always tempting to utilize such schemes in computer NL processors because they provide clear models for resolution that are both easy and cheap (in terms of steps involved) to implement. The problem with these schemes is that they can easily be made to fail by manipulating parameters that they 'know' nothing about, such as semantics, context, and intonation. Clearly, more elaborate schemes for attachment resolution are needed, but what these schemes should contain and how they should be implemented remain open. This study attempts to find answers to the question of how a computer program should resolve attachment by examining naturally occurring PP attachments in a typed dialogue domain drawn from a study by Brunner, Whittemore, Ferrara, and Hsu (1989). Various previously developed theories of PP attachment are tested against the data to see how well they predict correct attachments of PPs in the typed dialogues. The result of this effort will be a hypothesis of attachment resolution that seems to fit the data.