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Báo cáo khoa học: "An Extension of Earley's Algorithm for S-Attributed Grammars"

Attribute grammars are an elegant formalization of the augmented context-free grammars characteristic of most current natural language systems. This paper presents an extension of Earley's algorithm to Knuth's attribute grammars, considering the case of S-attributed grammars. For this case, we study the conditions on the underlying base grammar under which the extended algorithm may be guaranteed to terminate. Finite partitioning of attribute domains is proposed to guarantee the termination of the algorithm, without the need for any restrictions on the context-free base. . | An Extension of Earley s Algorithm for S-Attributed Grammars Nelson Correa Department of Electrical Engineering Universidad de los Andes Apartado Aéreo 4976 Bogotá D.E. Colombia bitnet NCORREA at ANDESCOL Abstract Auributc grammars arc an elegant formalization of the augmented context-free grammars characteristic of most current natural language systems. This paper presents an extension of Earley s algorithm to Knuth s attribute grammars considering the case of S-allributcd grammars. For this case we study the conditions on the underlying base grammar under which the extended algorithm may be guaranteed to terminate. Finite partitioning of attribute domains is proposed to guarantee the termination of the algorithm without the need for any restrictions on the context-free base. 1. Introduction Earley s 1970 algorithm is a general algorithm for context-free languages widely used in natural language processing King 1983 Shicbcr 1985 and syntactic pattern recognition Fu 1982 where the full generative power of context-free grammar is required. The original algorithm and its common implementations however assume the atomic symbols of context-free grammars thus limiting its applicability to systems with attributed symbols or attribute grammars Knuth 1968 . Attribute grammar is an elegant formalization of the augmented context-free grammars characteristic of most current NLP systems. It is more general than members of the family of unification-based grammar formalisms Kay 1985 Shicbcr 1986 mainly in that it allows and encourages the use of simpler attribution functions than unification for the definition of attribute values and hence can lead to computationally efficient grammatical definitions while maintaining the advantages of a well-understood declarative formalism. Attribute grammar has been used in the past by the author to define computational models of Chomsky s Government-binding theory from which practical parsing programs were developed Correa 1987a . Many .