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Overview

TRALE, a freeware system written in Prolog by Gerald Penn, is an extension to ALE, which integrates phrase structure parsing, semantic head-driven generation and constraint logic programming with typed feature structures as terms. The most important advantage of TRALE over ALE is that TRALE exactly implements the interpretation of typing that is customarily assumed in Head-Driven Phrase Structure Grammar (HPSG). It also provides more intuitive ways of declaring type hierarchies, defining macros and setting up constraints on types and feature structures. These differences are briefly discussed below.

Type Declarations

TRALE's type declarations are markedly different from ALE's. Type hierarchies are introduced in a file separate from the grammar file. The format of the type hierarchy, although not the same as what is recognized by ALE, is intuitively more appealing.

Subtype Covering

Unlike ALE, TRALE assumes that subtypes exhaustively cover their supertypes, i.e., that every object of a non-maximal type, t, is also of one of the maximal types subsumed by t. This is in accordance with HPSG's interpretation of subtyping.

Logical Variable Macros

In addition to ALE macros, TRALE introduces a new type of macros that make use of logical variables in their definitions. Logical variables entail structure-sharing if used more than once in a predicate. This is useful if one wants to ensure structure sharing in a description using macros.

Complex Antecedent Constraints

Again, as an add-on to ALE's capabilities, TRALE introduces a new type of constraints. These constraints accept feature descriptions as well as types in their antecedents. In addition, following common practice in linguistics, variables in the antecedent of constraints take scope over the consequent as well.

These differences are discussed in more detail in TRALE User's Guide downloadable from this site. More information on the fundamentals of the system can be found on ALE Homepage.

Beata Trawinski
Last modified: Sat Oct 8 11:12:15 CEST 2005