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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.
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