Paradigmatic Treatment of Arabic Morphology

This paper 1 presents a language to express morphological processes, concatenative or nonconcatenative. The language allows the definition of two kinds of paradigms: helping paradigms, which define partial morphological forms, and main paradigms, which combine two or more helping paradigms to define fully specified forms. 1 I n t r o d u c t i o n This paper presents a language to express morphological processes and shows how that language applies straightforwardly to Arabic morphology 2. This approach to morphology is directly compatible with unification-based frameworks in that lexical entries are feature structures, and morphological processes are related to unification of feature structures. This work departs from two-level morphology, which has been at the center of computational morphology since the implementation of URKIMMO (Koskenniemi 1983) and was applied to Arabic morphology first by Kay (1987), then by Beesley (1989, 1996), Kiraz (1994, 1996a) and to Syriac morphology by Kiraz (1996b). Two-level morphology is characterized by an emphasis on phonological (or orthographic) rules, and has a rudimentary treatment of morphology itself. The language presented in this paper proposes a declarative approach to morphology 3 1The research was supported by a grant from the Research Board of the University of Illinois at UrbanaChampaign. 2I would like to thank two anonymous reviewers for their helpful comments. 3Only inflectional morphology is discussed in this paper; but the approach can be extended to derivational morphology. in which morphological processes are represented as paradigms of relations between feature structures and orthographic/phonological forms. This approach is inspired from work done by Calder (1989) who uses paradigms to organize morphological information, and string equations to handle string operations. 2 O r g a n i z a t i o n o f t h e L e x i c o n The language described here supports an organization of the lexicon into three components: feature component, morphological component and lexical entries. The feature component is a hierarchy of types related by monotonic multiple inheritance. The morphological component is a set of paradigms which relate feature structures of the feature component to inflected forms. The lexicon of "stems" is a collection of roots which are related to inflected forms by the morphological component. As is customary in accounts of Arabic, roots are ordered lists of consonants. They are associated with relevant idiosyncratic information (mainly semantic, for example the particular meaning associated with each root). 3 D e s c r i p t i o n o f t h e L a n g u a g e 3.1 T h e F e a t u r e C o m p o n e n t The feature component consists of a hierarchy of grammatical objects constrained by relevant features, similar to the type hierarchy of Headdriven Phrase Structure Grammar (Pollard and Sag 1994). This allows to capture generalities common to classes of words and avoid redundancies in the lexicon of roots. For example, verbs are constrained to be of category verb.