Domain Dependent Natural Language Understanding

A MORPHOLOGICAL RECOGNIZER WITH SYNTACTIC AND PHONOLOGICAL RULES John Bear Artificial Intelligence Center SRI International 333 Ravenswood Ave Menlo Park, CA 94025 U.S.A. Abstract This paper describes a morphological analyzer which, when pars- ing a word, uses two sets of rules: rnles describing the syntax of words, and rules describing facts about orthography. 1 Introduction t In many natural language processing systems currently in use, the morphological phenomena are handled by programs which do not interpret any sort of rules, but rather contain references to specific morphemes, graphemes, and grammatical categories. Recently Kaplan, Kay, Koskennicmi, and Karttunen have shown how to construct morphological analyzers in which the descrip- tions of the orthographic and syntactic phenomena are separable from the code. This paper describes a system that builds on their work in the area of phonology/orthography and also has a well defined syntactic component which applies to the area of computational morphology for the first time some of the tools that have bccn used in syntactic analysis for quite a while. This paper has two main parts. The first deals with the or- thographic aspects of morphological analysis, the second with its syntactic aspects. The orthographic phenomena constitute a blend of phonology and orthography. The orthographic rules given in this paper closely resemble phoImlogical rules, both in form and fimctlon, but because their purpose is the description of orthographic facts, the words orthography and orthographic will be used in preference to phonology and phonological. The overall goal of the work described herein is the devel- opment of a flexible, usable morphological analyzer in which the rules for both syntax and spelling arc (1) separate from the code, and (2) descriptively powerful enough to handle the phenomena encountered when working with texts of written language. 2 Orthography The researchers mentioned above use finite-state transducers for stipulating correspondences between surface segments, and un- derlying segments. In contrast, the system described in this pa- ll am indebted to Lauri Karttunen and Fernando Pereir~ for all their help. Laurl supplied the initial English automat~ on which the orthographic grammar was based, while Fernando furnished some of the Prolog code. Both provided many helpful suggestion~ and explanations as well. I would also like to thank Kimmo Koskennlemi for his comments on an earlier draft of this paper. This research was supported by the following grants: Naval Electronics Systems Command N00039-84-K-0078; Navelex N00039-84-C-0524 P00003; Office of Naval Research N00014-85-C-0013. per does not use finite state machines. Instead, orthographic rules are interpreted directly, as constraints on pairings of sur- face strings with lexieal strings. Tile rule notation employed, including conventions for express- ing abbreviations, is based on that described in Koskenniemi [1983,1984]. Tile rules actually used in this system are based on tile account of English in Karttunen and Wittenburg [1983]. 2.1 Rules What follows is an inductive introduction to the types of rules needed. Some pertinent data will be presented, then some po- tential rules for handling these data. We shall also discuss the reasons for needing …

Content truncated to 500 words