TAILIEUCHUNG - Báo cáo khoa học: "AN EXTENDED OF HEAD-DRIVEN THEORY PARSING"

On the basis of work in [8] for nondeterministic left-to-right parsing, we trace here a theory of head-driven parsing going from crude top-down and head-corner to more sophisticated solutions, in the attempt to successively make more deterministic the behaviour of head-driven methods. Finally, we propose an original generalization of headdriven parsing, allowing a more detailed specification of the order in which elements of a right-hand side are to be processed. | AN EXTENDED THEORY OF HEAD-DRIVEN PARSING Mark-Jan Nederhof University of Nijmegen Department of Computer Science Toernooiveld 6525 ED Nijmegen The Netherlands markj Abstract We show that more head-driven parsing algorithms can be formulated than those occurring in the existing literature. These algorithms are inspired by a family of left-to-right parsing algorithms from a recent publication. We further introduce a more advanced notion of head-driven parsing which allows more detailed specification of the processing order of non-head elements in the right-hand side. We develop a parsing algorithm for this strategy based on LR parsing techniques. Introduction According to the head-driven paradigm parsing of a formal language is started from the elements within the input string that are most contentful either from a syntactic or more generally from an information theoretic point of view. This results in the weakening of the left-to-right feature of most traditional parsing methods. Following a pervasive trend in modern theories of Grammar consider for instance 5 3 11 the computational linguistics community has paid large attention to the head-driven paradigm by investigating its applications to context-free language parsing. Several methods have been proposed so far exploiting some nondeterministic head-driven strategy for context-free language parsing see among others 6 13 2 14 . All these proposals can be seen as generalizations to the head-driven case of parsing prescriptions originally conceived for the left-to-right case. The methods above suffer from deficiencies that are also noticeable in the left-to-right case. In fact when more rules in the grammar share the same head element or share some infix of their right-hand side including the head the recognizer nondeterministically guesses a rule just after having seen the head. In this way analyses that could have been shared are duplicated in the parsing process. Interesting techniques have been .

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