A Functional Approach to Generation with TAG

A Functional Approach to Generation with TAG 1 Kathleen F. McCoy, K. Vijay-Shanker, & Gijoo Yang Department of Computer and Information Sciences University of Delaware Newark, Delaware 19716, USA email: mccoy@udel.edu, vijay@udel.edu Abstract It has been hypothesized that Tree Adjoining Grammar (TAG) is particularly well suited for sentence generation. It is unclear, however, how a sentence generation system based on TAG should choose among the syntactic possibilities made available in the grammar. In this paper we con- sider the question of what needs to be done to generate with TAGs and explain a generation sys- tem that provides the necessary features. This approach is compared with other TAG-based gen- eration systems. Particular attention is given to Mumble-86 which, like our system, makes syntac- tic choice on sophisticated functional grounds. 1 Introduction Joshi (1987) described the relevance of Tree Adjoining Grammar (TAG) (Joshi, 1985; Sch- abes, Abeille &5 Joshi, 1988) to Natural Language Generation. In particular, he pointed out how the unique factoring of recursion and dependen- cies provided by TAG made it particularly appro- priate to derive sentence structures from an input provided by a text planning component. Of par- ticular importance is the fact that (all) syntactic dependencies and function argument structure are localizest in TAG trees. Shieber and Schabes (1991) discuss using Synchronous TAG for generation. Synchronous TAG provides a formal foundation to make ex- plicit the relationship between elementary syntac- tic structures and their corresponding semantic counterparts, both expressed as elementary TAG trees. This relationship is made explicit by pairing the elementary trees in the syntactic and logical form languages, and associating the correspond- ing nodes. Shieber and Schabes (1990) describe a generation algorithm which "parses" an input log- ical form string recording the adjoining and sub- stitution operations necessary to build the string from its elementary components. The correspond- ing syntactic structure is then generated by doing 1 This work is supported ill part by Grant #H133E80015 from the National hlstitute on Disability and Rehabilita- tion Research. Support was also provided by the Nemours Fotmdation. We would like to thank John Hughes for Iris many conunents and discussions concerning this work. the same. set of operations (in reverse. ) on the cor- responding elementary structures m the grammar describing the natural language. Note that the generation methodology pro- posed for synchronous TAG (and the hypotheti- cal generator alluded to in (Joshi, 1987)) takes as input the logical form semantic representation and produces a syntactic representation of a natu- ral language sentence which captures that logical form. While the correspondence between logical form and the natural language syntactic form is certainly an important and necessary component of any sentence generation system, it is unclear how finer distinctions can be made in this frame- work. That is, synchronous TAG does not address the question of which syntactic rendition of a par- ticular logical form is most appropriate in a given circumstance. This aspect is particularly crucial from the point of view of generation. A full-blown generation system based …

Content truncated to 500 words