D-Tree Grammars

D-Tree Grammars Owen Rambow CoGenTex, Inc. 840 Hanshaw Road Ithaca, NY 14850 owen@cogent ex. com K. Vijay-Shanker Department of Computer Information Science University of Delaware Newark, DE 19716 vii ay©udel, edu David Weir School of Cognitive & Computing Sciences University of Sussex Brighton, BN1 9HQ, UK. david, weir~cogs, susx. ac. uk Abstract DTG are designed to share some of the advantages of TAG while overcoming some of its limitations. DTG involve two com- position operations called subsertion and sister-adjunction. The most distinctive fea- ture of DTG is that, unlike TAG, there is complete uniformity in the way that the two DTG operations relate lexical items: subsertion always corresponds to comple- mentation and sister-adjunction to modi- fication. Furthermore, DTG, unlike TAG, can provide a uniform analysis for wh- movement in English and Kashmiri, des- pite the fact that the wh element in Kash- miri appears in sentence-second position, and not sentence-initial position as in Eng- lish. 1 Introduction We define a new grammar formalism, called D-Tree Grammars (DTG), which arises from work on Tree- Adjoining Grammars (TAG) (Joshi et al., 1975). A salient feature of TAG is the extended domain of lo- cality it provides. Each elementary structure can be associated with a lexical item (as in Lexicalized TAG (LTAG) (Joshi ~ Schabes, 1991)). Properties related to the lexical item (such as subcategoriza- tion, agreement, certain types of word order varia- tion) can be expressed within the elementary struc- ture (Kroch, 1987; Frank, 1992). In addition, TAG remain tractable, yet their generative capacity is suf- ficient to account for certain syntactic phenomena that, it has been argued, lie beyond Context-Free Grammars (CFG) (Shieber, 1985). TAG, however, has two limitations which provide the motivation for this work. The first problem (discussed in Section 1.1) is that the TAG operations of substitution and ad- junction do not map cleanly onto the relations of complementation and modification. A second pro- blem (discussed in Section 1.2) has to do with the inability of TAG to provide analyses for certain syn- tactic phenomena. In developing DTG we have tried to overcome these problems while remaining faith- ful to what we see as the key advantages of TAG (in particular, its enlarged domain of locality). In Sec- tion 1.3 we introduce some of the key features of DTG and explain how they are intended to address the problems that we have identified with TAG. 1,1 Derivations and Dependencies In LTAG, the operations of substitution and adjunc- tion relate two lexical items. It is therefore natural to interpret these operations as establishing a di- rect linguistic relation between the two lexical items, namely a relation of complementation (predicate- argument relation) or of modification. In purely CFG-based approaches, these relations are only im- plicit. However, they represent important linguistic intuition, they provide a uniform interface to se- mantics, and they are, as Schabes ~ Shieber (1994) argue, important in order to support statistical pa- rameters in stochastic frameworks and appropriate adjunction constraints in TAG. In many frameworks, complementation and …

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