Polynomial Tree Substitution Grammars: Characterization and New Examples
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چکیده
Polynomial Tree Substitution Grammars, a subclass of STSGs for which finding the most probable parse is no longer NP-hard but polynomial, are defined and characterized in terms of general properties on the elementary trees of the grammar. Necessary and sufficient conditions for effective polynomiality are first given. Then, various sufficient properties which are easier to compute are analyzed. The min-max selection principle is shown to be one such sufficient property. Another instance of sufficient properties, based on lexical heads, is also presented. The performances of both models are evaluated on several corpora.
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تاریخ انتشار 2007