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Phrase Structure Grammars

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The ALE phrase structure processing component is loosely based on a combination of the functionality of the PATR-II system and the DCG system built into Prolog. Roughly speaking, ALE provides a system like that of DCGs, with two primary differences. The first difference stems from the fact that ALE uses attribute-value logic descriptions of typed feature structures for representing categories and their parts, while DCGs use first-order terms (or possibly cyclic variants thereof). The second primary difference is that ALE's parser uses a bottom-up active chart parsing algorithm and a semantic-head-driven generator rather than encoding grammars directly as Prolog clauses and evaluating them top-down and depth-first. In the spirit of DCGs, ALE allows definite clause procedures to be attached and evaluated at arbitrary points in a phrase structure rule, the difference being that these rules are given by definite clauses in ALE's logic programming system, rather than directly in Prolog.

Phrase structure grammars come with two basic components, one for describing lexical entries and empty categories, and one for describing grammar rules. We consider these components in turn.



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TRALE User's Manual