tailieunhanh - Báo cáo khoa học: "Structure-Sharing in Lexical Representation"

The lexicon now plays a central role in our implementation of a Head-driven Phrase Structure G r a m m a r (HPSG), given the massive relocation into the lexicon of linguisticinformation that was carried by the phrase structure rules in the old G P S G system. HPSG's grammax contains fewer tha4z twenty (very general) rules; its predecessor required over 350 to achieve roughly the same coverage. This simplification of the grammax is made possible by an enrichment of the structure and content of lexical entries, using both inhcrit~nce mechanisms and lexical rules to represent thc linguistic. | Structure-Sharing in Lexical Representation Daniel Flickinger Carl Pollard and Thomas Wascw Hewlett-Packard Laboratories 1501 Page Mill Road Palo Alto CA. 94303 USA Abstract 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. HPSG s 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 generalizations 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. 1. Introduction The project we refer to as HPSG is the current phase of an ongoing effort at Hewlett-Packard Laboratories to develop an English language understanding system which implements current work in theoretical linguistics. Incorporating innovations in the areas of lexicon grammar parser and semantics HPSG is the successor to the GPSG system reported on at the 1982 ACL meeting1 Like the GPSG system the current implementation is based on the linguistic theory known as Generalized Phrase Structure Grammar 2 though incorporating insights from Carl Pollard s recent work on Head Grammars3 which lead US to employ a richer lexicon and a significantly smaller grammar. We report here on the structure of our lexicon the mechanisms used in its representation and the resulting sharp decrease in the number of phrase structure rules 1 Gawron et al. 1982 . 2 Gazdar Klein .