Browse Theses

This thesis presents new surface generation techniques that improve on both aspects of surface generation: (1) lexical choice, which consists of choosing words and their associated syntactic structures and (2) syntactic realization, which consists of combining these partial structures into grammatical sentences. The thesis investigates the impact of the pragmatic situation on surface generation. Because surface generation depends directly on many aspects of the situation, these new techniques allow a purely conceptual input to be expressed by a greater variety of linguistic forms and with more sensitivity to pragmatic factors than was previously possible.

Specifically, this research focuses on the impact on lexical choice of one part of the pragmatic situation: the speaker's argumentative intent, i.e., the goal of the speaker to convince the hearer of a certain conclusion. The argumentative intent can be realized by a variety of evaluative expressions appearing at various ranks in the syntactic structure. This thesis describes the selection of four classes of evaluative expressions: judgment determiners (i.e., many), scalar adjectives (i.e., difficult), connotative verbs (i.e., require, enjoy) and argumentative connectives (i.e., but, so). These four classes were not addressed in previous generators.

The scFUF formalism is introduced in this thesis to address the issue of complex constraint interaction arising when performing lexical choice under pragmatic constraints. scFUF is derived from Functional Unification Grammars (scFUGs), a formalism previously used for syntactic realization only. scFUF extends scFUGs by providing new mechanisms for control, for expressing hierarchical relations and for using modular knowledge sources. These extensions make scFUF capable of handling lexical choice. In addition, this thesis describes the use of scFUF to develop scSURGE, one of the largest and most widely used syntactic realization grammar available.

Finally these new generation techniques are applied to the implementation of scADVISOR II, a question-answering system helping students to choose classes for a semester. In particular, scADVISOR II uses the increased expressive flexibility provided by these techniques to convince a student to choose different classes by presenting the same objective data, retrieved from an underlying knowledge base, in different linguistic forms using evaluative expressions.