Daniel Flickinger

Structure-Sharing in Lexical Representation

The lexicon now plays a central role in our implementation of a Head-driven Phrase Structure Grammar (HPSG), given the massive relocation into the lexicon of linguistic information that was carried by the phrase structure rules in the old GPSG system. HPSGs grammar contains fewer than twenty (very general) rules; its predecessor required over 350 to achieve roughly the same coverage. This simplification of the grammar is made possible by an enrichment of the structure and content of lexical entries, using both inheritance mechanisms and lexical rules to represent the linguistic information in a general and efficient form. We will argue that our mechanisms for structure-sharing not only provide the ability to express important linguistic generalization about the lexicon, but also make possible an efficient, readily modifiable implementation that we find quite adequate for continuing development of a large natural language system.

Inheritance and complementation: a case study of easy adjectives and related nouns

Mechanisms for representing lexically the bulk of syntactic and semantic information for a language have been under active development, as is evident in the recent studies contained in this volume. Our study serves to highlight some of themost useful tools available for structured lexical representation, in particular (multiple) inheritance, default specification, and lexical rules. It then illustrates the value of these mechanisms in illuminating one corner of the lexicon involving an unusual kind of complementation among a group of adjectives exemplified by easy. The virtues of the structured lexicon are its succinctness and its tendency to highlight significant clusters of linguistic properties. From its succinctness follow two practical advantages, namely its ease of maintenance and modification. In order to suggest how important these may be practically, we extend the analysis of adjectival complementation in several directions. These further illustrate how the use of inheritance in lexical representation permits exact and explicit characterizations of phenomena in the language under study. We demonstrate how the use of the mechanisms employed in the analysis of easy enables us to give a unified account of related phenomena featuring nouns such as pleasure, and even the adverbs (adjectival specifiers) too and enough. Along the way we motivate some elaborations of the HPSG (head-driven phrase structure grammar) framework in which we couch our analysis, and offer several avenues for further study of this part of the English lexicon.