tailieunhanh - Báo cáo khoa học: "Inheritance and the CCG Lexicon"

I propose a uniform approach to the elimination of redundancy in CCG lexicons, where grammars incorporate inheritance hierarchies of lexical types, defined over a simple, feature-based category description language. The resulting formalism is partially ‘constraint-based’, in that the category notation is interpreted against an underlying set of tree-like feature structures. I argue that this version of CCG subsumes a number of other proposed category notations devised to allow for the construction of more efficient lexicons. The formalism retains desirable properties such as tractability and strong competence, and provides a way of approaching the problem of how to generalise CCG. | Inheritance and the CCG Lexicon Mark McConville Institute for Communicating and Collaborative Systems School of Informatics University of Edinburgh 2 Buccleuch Place Edinburgh EH8 9LW Scotland Abstract I propose a uniform approach to the elimination of redundancy in CCG lexicons where grammars incorporate inheritance hierarchies of lexical types defined over a simple feature-based category description language. The resulting formalism is partially constraint-based in that the category notation is interpreted against an underlying set of tree-like feature structures. I argue that this version of CCG subsumes a number of other proposed category notations devised to allow for the construction of more efficient lexicons. The formalism retains desirable properties such as tractability and strong competence and provides a way of approaching the problem of how to generalise CCG lexicons which have been automatically induced from treebanks. 1 The CCG formalism In its most basic conception a CCG over alphabet s of terminal symbols is an ordered triple A S L where A is an alphabet of saturated category symbols S is a distinguished element of A and L is a lexicon . a mapping from s to categories over A. The set of categories over alphabet A is the closure of A under the binary infix connectives and and the associated modalities of Baldridge 2002 . For example assuming the saturated category symbols S and NP here is a simple CCG lexicon modalities omitted 1 John I- NP Mary H NP loves I- S NP NP The combinatory projection of a CCG lexicon is its closure under a finite set of resource-sensitive combinatory operations such as forward application 2 backward application 3 forward type raising 4 and forward composition 5 2 X Y Y X 3 Y X Y X 4 X Y Y X 5 X Y Y Z X Z CCG A S L over alphabet s generates string s E s just in case s S is in the combinatory projection of lexicon L. The derivation in Figure 1 shows that CCG 1 generates the sentence John loves .