Feature-Based Allomorphy

Morphotactics and allomorphy are usually modeled in different components, leading to interface problems. To describe both uniformly, we define finite automata (FA) for allomorphy in the same feature description language used for morphotactics. Nonphonologically conditioned allomorphy is problematic in FA models but submits readily to treatment in a uniform formalism. 1 Background and Goals ALLOMORPHY or MORPHOPHONEMICS describes the variation we find among the different forms of a morpheme. For instance, the German second person singular present ending-st has three different allomorphs,-st,-est,-t, determined by the stem it combines with: 'say' 'pray' 'mix' (1) lsg pres ind 2sg pres ind 3sg pres ind sag+e sag+st sag+t bet + e bet+ est bet-/-et mix+e mix+t mix+t MORPHOTACTICS describes the arrangement of morphs in words, including, e.g., the properties of-st that it is a suffix (and thus follows the stem it combines with), and that it combines with verbs. While allomorphy is normally described in finite automata (FA), morphotactics is generally described in syntax-oriented models, e.g., CFGs or feature-based grammars. The present paper describes both allomor-phy and morphotactics in a feature-based language like that of Head-Driven Phrase Structure Grammar (HPSG) (Pollard and Sag 1987). 9002 0 from the German Bundesministerium ffir Forschung und Technologie to the DFKI DISCO project. We are grateful to an anonymous ACL reviewer for helpful comments. The technical kernel of the paper is a feature-based definition of FA. 1 While it is unsurprising that the languages defined by FA may also be defined by feature description languages (FDL), our reduction goes beyond this, showing how the FA themselves may be defined. The significance of specifying the FA and not merely the language it generates is that it allows us to use FA technology in processing allomorphy, even while keeping the interface to other grammar components maximally transparent (i.e., there is NO interface-all linguistic information is specified via FDL). Our motivation for exploring this application of typed feature logic is the opportunity it provides for integrating in a single descriptive formalism not only (i) allomorphic and morpho-tactic information but also (ii) coneatenative and non-concatenative allomorphy. The latter is particularly useful when concatenative and non-concatenative allomorphy coexists in a single language, as it does, and F _C Q the set of FINAL STATES. 2 For reasons of simplicity and space, we only refer to the simplest form of FA, viz., DETERMIN-ISTIC finite automata without e-moves which consume exactly one input symbol …