Triphone Analysis: A Combined Method for the Correction of Orthographical and Typographical Errors.

TRIPHONE ANALYSIS: A COMBINED METHOD FOR THE CORRECTION OF ORTHOGRAPHICAL AND TYPOGRAPHICAL ERRORS. Brigitte van Berkelt and Koenraad De Smedt* 1" Institute for Applied Computer Science (ITI), TNO Schoemakerstraat 97, 2628 VK Delft, The Netherlands *Language Technology Project, Psychology Dept., University of Nijmegen Montessofilaan 3, 6525 HR Nijmegen, The Netherlands ABSTRACT Most existing systems for the correction of word level errors are oriented toward either typographical or orthographical errors. Triphone analysis is a new correction strategy which combines phonemic transcription with trigram analysis. It corrects both kinds of errors (also in combination) and is superior for orthographical errors. 1. INTRODUCTION 1.1 Error types Any method for the correction of word level errors in written texts must be carefully tuned. On the one hand, the number of probable corrections should be maximized; on the other hand, the number of unlikely corrections should be minimized. In order to achieve these goals, the characteristics of specific error types must be exploited as much as possible. In this article we distinguish two major types of word level errors: orthographical errors and typographical errors. They have some clearly different characteristics. Orthographical errors are cognitive errors consisting of the substitution of a deviant spelling for a correct one when the author either simply doesn't know the correct spelling for a correct spelling, forgot it, or misconceived it. An important characteristic of orthographical errors is that they generally result in a string which is phonologically identical or very similar to the correct string (e.g. indicies instead of indices1). As a consequence, orthographical errors are dependent on the correspondence between spelling and pronunciation in a particular language. Another characteristic is that proper names, infrequent words and foreign words are particularly prone to ortho- graphical errors. 1 All examples of errors given in this article were actually found by the authors in texts written by native speakers of the language in question. Typographical errors are motoric errors caused by hitting the wrong sequence of keys. Hence their char- acteristics depend on the use of a particular keyboard rather than on a particular language. Roughly eighty percent of these errors can be described as single dele- tions (e.g. continous) insertions (e.g. explaination), substitutions (e.g. anyboby) or transpositions (e.g. autoamtically) while the remaining twenty percent are complex errors (Peterson, 1980). Some statistical facts about typographical errors are that word-initial errors are rare, and doubling and undoubling (e.g. succeeed, discusion) are common. In general, typographical errors do not lead to a string which is homophonous with the correct string. Most of the correction methods currently in use in spelling checkers are biased toward the correction of typographical errors. We argue that this is not the fight thing to do. Even if orthographical errors are not as frequent as typographical errors, they are not to be neglected for a number of good reasons. First, orthographical errors are cognitive errors, so they are more persistent than typographical errors: proof- reading by the author himself will often fail to lead to correction. Second, orthographical errors …

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