Evaluation of LTAG parsing with supertag compaction

One of the biggest concerns that has been raised over the feasibility of using large-scale LTAGs in NLP is the amount of redundancy within a grammar¿s elementary tree set. This has led to various proposals on how best to represent grammars in a way that makes them compact and easily maintained (Vijay-Shanker and Schabes, 1992; Becker, 1993; Becker, 1994; Evans, Gazdar and Weir, 1995; Candito, 1996). Unfortunately, while this work can help to make the storage of grammars more efficient, it does nothing to prevent the problem reappearing when the grammar is processed by a parser and the complete set of trees is reproduced. In this paper we are concerned with an approach that addresses this problem of computational redundancy in the trees, and evaluate its effectiveness

The LEXSYS project

this paper, at the point where lemmas are associated with tree families: each lemma / family combination would have a separate probability. Carroll and Weir (1997) outline other alternative probabilistic models, some of which we also intend to investigate

Parsing with an extended domain of locality

One of the claimed benefits of Tree Ad- joining Grammars is that they have an extended domain of locality (EDOL). We consider how this can be exploited to limit the need for feature structure uni- fication during parsing. We compare two wide-coverage lexicalized grammars of English, LEXSYS and XTAG, finding that the two grammars exploit EDOL in different ways

Grammar compaction and computation sharing in automaton-based parsing

Wide-coverage grammars in Lexicalised TreeAdjoining Grammar (ltag) and related formalisms are structurally complex, containing many hundreds of elementary trees. In the context of the development of a full-scale ltag-like grammar and parsing system, we have investigated the claim that because many of these trees have a great deal of structure in common, a parser that manipulates trees individually performs a considerable amount of redundant computation. This claim has been used to motivate a parsing technique that encodes trees as finite state automata and captures overlapping computation through automata minimization. Our preliminary results show that this technique leads to considerable computation sharing. 1 Introduction The paper presents work that forms part of the ongoing LexSys project 1 . Our overall aim is to bring together and test in practice a variety of current nlp techniques, including the organisation of grammars into inheritance hierarchies for compact representati..

Evaluation of LTAG parsing with supertag compaction

One of the biggest concerns that has been raised over the feasibility of using large-scale LTAGs in NLP is the amount of redundancy within a grammar’s elementary tree set. This has led to various proposals on how best t

Engineering a wide-coverage lexicalized grammar

We discuss a number of practical issues that have arisen in the development of a wide-coverage lexicalized grammar for English. In particular, we consider the way in which the design of the grammar and of its encoding was influenced by issues relating to the size of the grammar