A Construction-Specific approach to Focused Interaction in Flexible Parsing

A Construction-Specific Approach to Focused Interaction in Flexible Parsing Philip J. Hayes Carnegie-Mellon University Pittsburgh, PA 15213 Abstract ~ A flexible parser can deal with input that deviates from its grammar, in addition to input that conforms to it. Ideally, such a parser will correct the deviant input: sometimes, it will be unable to correct it at all; at other times, correction will be possible, but only to within a range of ambiguous possJbilities. This paper is concerned with such ambiguous situations, and with making it as easy as possible for the ambiguity to be resolved through consultation with the user of the parser - we presume interactive use. We show the importance of asking the user for clarification in as focused a way as possible. Focused interaction of this kind is facilitated by a construction. specific approach to flexible parsing, with specialized parsing techniques for each type of construction, and specialized ambiguity representations for each type of ambiguity that a particular construction can give rise to. A construction-specific approach also aids in task-specific language development by allowing a language definibon that is natural in terms of the task domain to be interpreted directly without compilation into a uniform grammar formalism, thus greatly speeding the testing of changes to the language definition. 1. Introduction There has been considerable interest recently in the topic of flexible parsing, i.e. the parsing of input that deviates to a greater or lesser extent from the grammar expected by the parsing system. This iriterest springs from very practical concerns with the increamng use of natural language in computer interfaces. When people attempt to use such interfaces, they cannot be expected always to conform strictly to the interfece's grammar, no matter how loose and accomodating that grammar may be. Whenever people spontaneously use a language, whether natural or artificial, it is inevitable that they will make errors of performance. Accordingly, we [3] and other researchers including Weischedel and Black [6], and Kwasny and Sondheimer [5], have constructed flexible parsers which accept ungrammatical input, correcting the errors whenever possible, generating several alternative interpretations if more than one correction is plausible, and in cases where the input cannot be massaged into lull grammaticality, producing as complete a partial parse as possible. If a flexible parser being used as part of an interactive system cannot correct ungrammatical input with total, certainty, then the system user must be involved in the resolution of the difficulty or the confirmation of the parser's Correction. The approach taken by Weischedel and Black [6] in such situations is to inform the user about the nature of the difficulty, in the expectation that he will be able to use this information to produce a more acceptable input next time, but this can involve the user in substantial retyping. A related technique, adopted by the COOP system [4], is to paraphrase back tO the user the one or more parses that the system has produced from the user!s input, and to allow the user to confirm …

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