tailieunhanh - Báo cáo khoa học: "Wrapping of Trees"

We explore the descriptive power, in terms of syntactic phenomena, of a formalism that extends TreeAdjoining Grammar (TAG) by adding a fourth level of hierarchical decomposition to the three levels TAG already employs. While extending the descriptive power minimally, the additional level of decomposition allows us to obtain a uniform account of a range of phenomena that has heretofore been difficult to encompass, an account that employs unitary elementary structures and eschews synchronized derivation operations, and which is, in many respects, closer to the spirit of the intuitions underlying TAG-based linguistic theory than previously considered extensions to TAG. . | Wrapping of Trees James Rogers Department of Computer Science Earlham College Richmond IN 47374 USA jrogers@ Abstract We explore the descriptive power in terms of syntactic phenomena of a formalism that extends TreeAdjoining Grammar TAG by adding a fourth level of hierarchical decomposition to the three levels TAG already employs. While extending the descriptive power minimally the additional level of decomposition allows us to obtain a uniform account of a range of phenomena that has heretofore been difficult to encompass an account that employs unitary elementary structures and eschews synchronized derivation operations and which is in many respects closer to the spirit of the intuitions underlying TAG-based linguistic theory than previously considered extensions to TAG. 1 Introduction Tree-Adjoining Grammar TAG Joshi and Schabes 1997 Joshi et al. 1975 is a grammar formalism which comes with a well-developed theory of natural language syntax Frank 2002 Frank 1992 Kroch and Joshi 1985 . There are however anum-ber of constructions many in the core of language which present difficulties for the linguistic underpinnings of TAG systems although not necessarily for the implemented systems themselves. Most of these involve the combining of trees in ways that are more complicated than the simple embedding provided by the tree-adjunction operation. The most widely studied way of addressing these constructions within TAG-based linguistic theory Kroch and Joshi 1987 Kroch 1989 Frank 2002 has been to assume some sort of multi-component adjoining MCTAG Weir 1988 in which elementary structures are factored into sets of trees that are adjoined simultaneously at multiple points. Depending on the restrictions placed on where this adjoining can occur the effect of such extensions range from no increase in complexity of either the licensed tree sets or the computational complexity of parsing to substantial increases in both. In this paper we explore these issues .