TAILIEUCHUNG - Báo cáo khoa học: "Head-driven Parsing for Lexicalist Grammars: Experimental Results"

We present evidence that head-driven parsing strategies lead to efficiency gains over standard parsing strategies, for lexicalist, concatenative and unification-based grammars. A head-driven parser applies a rule only after a phrase matching the head has been derived. By instantiating the head of the rule important information is obtained about the left-hand-side and the other elements of the right-hand-side. We have used two different head-driven parsers and a number of standard parsers to parse with lexicalist grammars for English and for Dutch. . | Head-driven Parsing for Lexicalist Grammars Experimental Results Gosse Bouma Gertjan van Noord vakgroep Alfa-informatica University of Groningen Postbus 716 NL 9700 AS Groningen Abstract We present evidence that head-driven parsing strategies lead to efficiency gains over standard parsing strategies for lexicalist concatenative and unification-based grammars. A head-driven parser applies a rule only after a phrase matching the head has been derived. By instantiating the head of the rule important information is obtained about the left-hand-side and the other elements of the right-hand-side. We have used two different head-driven parsers and a number of standard parsers to parse with lexicalist grammars for English and for Dutch. The results indicate that for important classes of lexicalist grammars it is fruitful to apply parsing strategies which are sensitive to the linguistic notion head . 1 Introduction Lexicalist grammar formalisms such as Head-driven Phrase Structure Grammar HPSG and Categorial Unification Grammar CUG have two characteristic properties. Lexical elements and phrases are associated with categories that have considerable internal structure. Second instead of construction specific rules a small set of generic rule schemata is used. Consequently the set of constituent structures defined by a grammar cannot be read off the rule set directly but is defined by the interaction of the rule schemata and the lexical categories. Applying standard parsing algorithms to such grammars is unsatisfactory for a number of reasons. Earley parsing is intractable in general as the rule set is simply too general. For some grammars naive top-down prediction may even fail to terminate. Shieber 1985 therefore proposes a modified version of the Earley-parser using restricted topdown prediction. While this modification leads to termination of the prediction step in practice it easily leads to a trivial top-down prediction step thus leading to inferior performance. .

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