TAILIEUCHUNG - Báo cáo khoa học: "SOME CHART-BASED TECHNIQUES FOR PARSING ILL-FORMED INPUT"

We argue for the usefulness of an active chart as the basis of a system that searches for the globally most plausible explanation of failure to syntactically parse a given input. We suggest semantics-free, grammarindependent techniques for parsing inputs displaying simple kinds of ill-formedness and discuss the search issues involved. THE PROBLEM Although the ultimate solution to the problem of processing ill-formed input must take into account semantic and pragmatic factors, nevertheless it is important to understand the limits of recovery strategies that age based entirely on syntax and which are independent of any particular grammar. . | SOME CHART-BASED TECHNIQUES FOR PARSING ILL-FORMED INPUT Chris s. Mellish Department of Artificial Intelligence University of Edinburgh 80 South Bridge EDINBURGH EH1 1HN Scotland. ABSTRACT We argue for the usefulness of an active chart as the basis of a system that searches for the globally most plausible explanation of failure to syntactically parse a given input We suggest semantics-free grammarindependent techniques for parsing inputs displaying simple kinds of ill-formedness and discuss the search issues involved. THE PROBLEM Although the ultimate solution to the problem of processing ill-famed input must take into account semantic and pragmatic factors nevertheless it is important to understand the limits of recovery strategies that are based entirely on syntax and which are independent of any particular grammar. The aim of this work is therefore to explore purely syntactic and grammar-independent techniques to enable a parser to recover from simple kinds of ill-formedness in textual inputs. Accordingly we present a generalised parsing strategy based on an active chart which is capable of diagnosing simple errors unknown misspelled words omitted words extra noise words in sentences from languages described by context free phrase structure grammars without eproductions . This strategy has the advantage that die recovery process can run after a standard active chart parser has terminated unsuccessfully without causing existing work to be repeated a the original parser to be stowed down in any way and that unlike previous systems it allows the full syntactic context to be exploited in the determination of a best parse fa an ill-formed sentence. EXPLOITING SYNTACTIC CONTEXT Weischedel and Sondheimer 1983 present an approach to processing ill-formed input based on a modified ATN parser. The basic idea is when an initial parse fails to select the incomplete parsing path that consumes the longest initial portion of the input apply a special rule to allow the blocked

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