The application of two-level morphology to non-concatenative German morphology

In this paper2 I describe a hybrid system for morphological analysis and synthesis. This system consists of two parts. The treatment of morphonology and non-concatenative morphology is based on the two-level approach proposed by Koskenniemi (1983). For the concatenative part of morphosyntax (i.e. affixation) a grammar based on featureunification is made use of. Both parts rely on a morph lexicon. Combinations of two-level morphology with feature-based morphosyntactic grammars have already been proposed by several authors (c.f. Bear 1988a, Carson 1988, Görz & Paulus 1988, Schiller & Steffens 1989) to overcome the shortcomings of the continuationclasses originally proposed by Koskenniemi (1983) and Karttunen (1983) for the description of morphosyntax. But up to now no linguistically satisfying solution has been proposed for the treatment of non-concatenative morphology in such a framework. In this paper I describe an extension to the model which will allow for the description of such phenomena. Namely it is proposed to restrict the applicability of two-level rules by providing them with filters in the form of feature structures. It is demonstrated how a wellknown problem of German morphology, so-called "Umlautung", can be described in this approach in a linguistically motivated and efficient way. 1 Work on this project has begun when I was working for the Austrian Research Institute for Artificial Intelligence in Vienna, Austria. 2 I want to thank my collegues Greg Dogil, Wolfgang Heinz, Tibor Kiss and Günter Neumann for fruitful discussions and helpful comments on earlier versions of this paper.