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Báo cáo khoa học: "Generative Power of CCGs with Generalized Type-Raised Categories"

This paper shows that a class of Combinatory Categorial Grammars (CCGs) augmented with a linguistically-motivated form of type raising involving variables is weakly equivalent to the standard CCGs not involving variables. The proof is based on the idea that any instance of such a grammar can be simulated by a standard CCG. | Generative Power of CCGs with Generalized Type-Raised Categories Nobo Komagata Department of Computer and Information Science University of Pennsylvania Philadelphia PA 19104 komagata@linc.cis.upenn.edu Abstract This paper shows that a class of Combinatory Categorial Grammars CCGs augmented with a linguistically-motivated form of type raising involving variables is weakly equivalent to the standard CCGs not involving variables. The proof is based on the idea that any instance of such a grammar can be simulated by a standard CCG. 1 Introduction The class of Combinatory Categorial Grammars CCG-Std was proved to be weakly equivalent to Linear Index Grammars and Tree Adjoining Grammars Joshi Vijay-Shanker and Weir 1991 Vijay-Shanker and Weir 1994 . But CCG-Std cannot handle the generalization of type raising that has been used in accounting for various linguistic phenomena including coordination and extraction Steedman 1985 Dowty 1988 Steedman 1996 prosody Prevost and Steedman 1993 and quantifier scope Park 1995 . Intuitively all of these phenomena call for a non-traditional more flexible notion of constituency capable of representing surface structures including Subj V Obj in English. Although lexical type raising involving variables can be introduced to derive such a constituent 1 unconstrained use of variables can increase the power. For example a grammar involving T x T y can generate a language AnBnCnDnE which CCG-Std cannot Hoffman 1993 . This paper argues that there is a class of grammars which allows the use of linguistically-motivated form of type raising involving variables while it is still weakly equivalent to CCG-Std. A class of grammars CCG-GTRC is inttoduced in the next section as an extension to CCG-Std. Then we show that CCG-GTRC can actually be simulated by a CCG-Std proving the equivalence. Thanks to Mark Steedman Beryl Hoffman Anoop Sarkar and the reviewers. The research was supported in part by NSF Grant Nos. IRI95-04372 STC-SBR-8920230 ARPA Grant