Arabic Finite-State Morphological Analysis and Generation

Arabic Finite-State Morphological Analysis and Generation Kenneth R. Beesley Rank Xerox Research Centre Grenoble Laboratory Le Quartz 6, chemin de Maupertuis 3824O MEYLAN France ken. beesley@xerox, fr Abstract This paper describes a large-scale sys- tem that performs morphological anal- ysis and generation of on-line Arabic words represented in the standard or- thography, whether fully voweled, par- tially voweled or unw)weled. Analyses display the root, pattern and all other affixes together with feature tags in- dicating part of speech, person, num- ber, mood, voice, aspect, etc. The system is based on lexicons and rules from an earlier KIMMO-style two-level morphological system, reworked exten- sively using Xerox Finite-State Morphol- ogy tools. The result is an Arabic Finite- State Lexical Transducer that is applied with the same runtime code used for English, French, German, Spanish, Por- tuguese, Dutch and Italian lexical tran~ ducers. 1 Introduction 1.1 Challenges of Arabic Morphology Semitic languages like Arabic present unusual challenges to automatic morphological analysis and generation. The first challenge is morpho- tactic: whereas most languages construct words out of morphemes which are just concatenated one after another, as in un-t-fail+ing-t-ly, an Arabic stem like daras (&,3.~) 1 is traditionally analyzed as consisting of a three-consonant root, transliter- ated as drs (0~ .~ ~), which is interdigitated with a pattern CaCaC, where C represents a slot for a root consonant, sometimes termed a radical; var- ious prefixes and suffixes can then concatenate to the stem in the familiar way. See Figure 1. Similarly, the root klb (~,. c.~ "-J) interdigitates with the same pattern to form katab (.~; and 1The Arabic examples in this paper were produced using the ArabTeX package for TEX and ~:I'EX by :Professor Klaus Lagally. Abstract lexical level: CaCaC wa+ +at d r s Abstract intersected level: wa+daras+at Figure 1: Abstract wa-l-daras-l-at ("and she learned/studied") the root brj (.~ j ~.) iuterdigitates with the pat- tern taCaC-aC to form the stein tabar-aj (~.~.:). There are perhaps 5000 Arabic roots in common usage, and about 400 phonologically distinct pat- terns, most of which are ambiguous. Each root can legally combine with only a small subset of the phonologically distinct patterns, an average of about seventeen or eighteen, and this decid- edly derivational process must be controlled by old-fashioned lexicography. The second challenge is that standard Arabic surface orthography seldom represents short vow- els, distinctive consonant length, and other po- tentially helpful details. The wa+daras+at exam- pie could conceivably be written fully roweled as wadarasal (~.aSJ~) , but it is much more likely to appear ms tile unvoweled wdrst (,~.., p_~). The re- suiting incompleteness of the surface orthography makes written text unusually ambiguous, with an average of ahnost five valid morphological anal- yses per word. Finally, Arabic orthography dis- plays an idiosyncratic mix of deep morphophono- logical elements carried to the surface, resulting in silent letters, and more surfacy representations of epenthesis, deletion and assimilation. 1.2 ChMlenges of Arabic Lexical Lookup Standard Arabic dictionaries like the Wehr-Cohen are organized by root headwords like drs …

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