Schema Method: A Framework for Correcting Grammatically Ill-formed Input

Schema Method: A Framework for Correcting Grammatically Ill-formed Input Ikuo KUD01) , Hideya KOSHINO2) , Moonkyung CHUNG2) and Tsuyosi MORIMOTO1) 1)ATR Interpreting Telephony Research Laboratories Twin 21 Building MID Tower 2-1-61 Shiromi, Higashi-ku Osaka 540, Japan 2)CSK Research Institute 3-22-17 Higashi-Ikebukuro, Toshima-ku Tokyo 170, Japan Abstract The schema method is a framework for correcting grammatically ill-formed input. In a natural language processing system ill-formed input cannot be overlooked. A computer assisted instruction (CAD system, in particular, needs to show the user's errors. This framework diagnoses ill-formed input, corrects it and explains the error, if an input is ill-~'ormed. The framework recognizes a sentence at two steps: first parses weak grammar, and then strongly filters the parsed sentence. When it is known what sentences are passed by the filter, it can be used even if it is imperfect. As the strong filter, a new method is used: an interpretation schema and an interpretation rule. An interpretation schema collects input information schemata and then an interpretation rule judges whether the collected schemata are correct or incorrect. This approach overcomes the problem of relaxation control, the major drawback of the previous syntactically-oriented methods, and is also more efficient. 1° Introduction Ill-formed input cannot be ignored when a natural language processing system such as a computer assisted instruction (CAD system or a machine translation system is built. Particularly in a CAI System, students often make mistakes, such as mispunctuation, lack of agreement, misplaced/improperly-used words, etc. In these cases, a CAI system needs to point out input errors, and show why the input it~ wrong. In order to do so, the system needs to diagnose and correct ill-formed input to explain the errors. The schema method as a framework for correcting grammatically ill-formed input is suggested and the diagnosis and correction of errors is discussed. There have been many studies for processing ill-formed input for English. The point of those studi.es is the diagnosis: how does the system find an error? The approaches are classified into two groups: the syntactically-oriented group and the frame-based group. The syntactically-oriented group includes robust parsers based on Augmented Transition Networks (ATN) which Use the relaxation technique/Kwansny 1981./or the meta-rule/Weisehedel 1980, 82, 87/, and the EPISTLE system which addresses the problems of the checking grammar and style of texts, such as letters, reports and manuals, written in ordinary English/Heidorn 1982/, /Jensen 1983/. The frame-based group attempts to deal with ungramnmtical input through extensions to pattern matching parsing/Hayes 1981/, through conceptual case frame instantiation/Schank 1980/and through approaches involving multiple cooperating parsing strategies /Carbonell 1983/. The target of that study is dialogue phenomena in communication with limited-domain systems, such as data-base systems, electronic mail systems, etc. The aim of this study is error-correction of non-native speakers written English text. This approach is syntactically oriented. The syntactically-oriented approaches/Kwansny 1981/ /Weischedel 1980,82,87/,/Heidorn 1982/,/Jensen 1983/are very similar. Their basic idea is relaxation. They first attempt to parse the input, using fully grammatical rules. If the sentence is not parsed, some of the conditions are relaxed. …

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