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Syntactics briefing

August 19, 2005 10:44 AM EST | Science | Email to Friend

The research in the field of Natural Language Processing usually assumes the existence of a syntactic "Generative Engine" that combines words and word-like elements into syntactic structures, and then sometimes displaces them by "syntactic movement". A Linguistic Parser must "undo" all the effects of syntactic movement, which results in a structure where the relations between the words are represented more directly.

In recent years, a new theoretical framework was introduced, in which the syntactic combinatorial system does not stop at the level of the words. Instead, the same "Generative Engine" continues all-the-way-down into morphology. The various parts of the same word correspond to the different areas of the syntactic tree, and then are brought together by multiple applications of movement.

Within this Constructionalist Framework, the syntactic is not a tree of words - it is a tree made of sub-lexical elements like roots, prefixes, suffixes, etc. The components of a single verb are spread all over the parse tree.

Correspondingly, the function of a Linguistic Parser is different. The goal of the parsing is to "reconstruct" every such sub-lexical element into its original place in the syntactic tree.

By undoing the effects of syntactic movement, "Constructionalist Parsing" produces the syntactic trees where atomic constituents of every word are distributed through such a "reconstructed" syntactic tree. Every constituent is restored into its appropriate location in the tree, where the context for its semantic contribution is found in immediately adjacent locations.

Deep Parsing makes it possible for all the relations between the elements in the tree to be strictly local.

The primary distinctive property of "Constructionalist Parsing" is the fact that the meaning of all the elements of a syntactic tree is determined locally.

The argument structures of all the verbs are represent by a small number of "functional elements". These "functional elements" introduce arguments and determine the semantic roles of the immediately adjacent Noun Phrases.

The state-of-art algorithms of "pattern matching" generally fail to produce good results on natural language text, before or after parsing. But when text undergoes "Constructionalist Parsing",
the output is more accessible to standard "pattern matching" methods and analysis, because an appropriate representation of text is generated that is in the domain of real Computer Science.

Sasson Margaliot is the founder of Linguistic Agents Ltd (www.linguisticagents.com)

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