Morphology with a Null-Interface

Morphology with a Null-Interface Harald Trost and Johannes Matiasek Austrian Research Institute for ArtificiM Intelligence.* Scllottengasse 3, A-IOIO Vienna, Austria {harald, john} 0ai. univie, ac. at Abstract We present an integrated architecture for word-level and sentence-level processing in a unification-based paradigm. The core of the sys- tem is a CLP implementation of a nnilication en- gine for feature structures suplmrting relational values. In this framework an IiPSC,-style granl- mar is implemented. Word-level processing uses X2MoltF, a morphological component I)ased on an extended version of two-level morphology. This component is tightly integrated with the grammar as a relation. The advantage of this apl)roach is that morphology and syntax are kept logically au- tonomous while at the same time minimizing in- terface problems. 1 Introduction Over the last few years there has 1)eeu a growing interest in computational morphology and phonol- ogy. A number of systems have been developed that deal with word-level processing. A widely used approach is finite-state morphology, most no- tably two-level morphology (for an introduction, see Sproat 92). Morphological components are sueeessflflly used for a wide range of stand-alone applications like sl)elling correction aM hyphen- ation. One obvious application is the use in NI,P systems geared to the analysis/generation of text. Surprisingly, they have not been widely al)l)lied in this domain up to now. A major reason for this is the llrolllem of interfacing morphology with syntax. Reflecting tile current trend in syntax towards lexicalism, unification-1)ased systems use highly structured feature structures as inI)ut. Translating tile out- put of morphologieM components into such it rel)- resentation has proved to be diiticult. Reducing interface problems is therefore crucial to success. *Financial support for the Austrian Research Institute for Artificial Intelligence is provkled by the Austrian Min- istry o] Science and Research. We wouhl like to thank Wolfgang lleinz for vMuable comments and suggestimls A tight integration between word and sen- tence level processing also has linguistic advan- tages. The boundary between morphology and syntax is fuzzy. When processing written text the units nmrl>hology has to deal with are, ill it tech- nicM sense, not words Mt character strings sepa- rated by delimiters. While these strings roughly correspond to the words of a sentence there are problematic cases. In German, e.g., zu-infinitive or w'rbs with separMfie prefixes ;Lre written as a single unit in some instances and separately ill others. The prol)lem has boon recognized and seine possihle remedies have been prol)osed. They all try to minimize or to elhninMe the intel'r:tce be- tweell word and sontoiic(: low4 processing. One stop is the descriptiml of word fl)rmation ill terms of a unification-based gl'all/lnai' to make the result (~1' morphological l)rocessing dir(,ctly ~wMhd)le to syntax and vice w~rsa, an :g)l)roa(-h ah'eady ti~ken in X2Moltl,' (Trost 90, '['rost 91), an extension of two-hwel nmrphohlgy. The harder probhml is the integration of mor- phol)honology which is traditionally formalized in it way not easily t,':mshmdlle into the fei~ture for- malisnx. We will show how this can he achieved by merging the word-level grammar of …

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