Using default inheritance to describe LTAG

TL;DR

This paper explores representing LTAG elementary trees using DATR's default inheritance, simplifying the encoding process and integrating tree structures within feature theories.

Contribution

It demonstrates how DATR's default inheritance can effectively encode LTAG elementary trees without additional formalism, streamlining lexical knowledge representation.

Findings

Default inheritance reduces the need for explicit dominance relations.

Tree structures can be embedded in feature theories similar to HPSG.

Lexical rules can be expressed as relations over feature structures.

Abstract

We present the results of an investigation into how the set of elementary trees of a Lexicalized Tree Adjoining Grammar can be represented in the lexical knowledge representation language DATR (Evans & Gazdar 1989a,b). The LTAG under consideration is based on the one described in Abeille et al. (1990). Our approach is similar to that of Vijay-Shanker & Schabes (1992) in that we formulate an inheritance hierarchy that efficiently encodes the elementary trees. However, rather than creating a new representation formalism for this task, we employ techniques of established utility in other lexically-oriented frameworks. In particular, we show how DATR's default mechanism can be used to eliminate the need for a non-immediate dominance relation in the descriptions of the surface LTAG entries. This allows us to embed the tree structures in the feature theory in a manner reminiscent of HPSG subcategorisation frames, and hence express lexical rules as relations over feature structures.