Smart Paradigms and the Predictability and Complexity of Inflectional Morphology

Proceedings of the 13th Conference of the European Chapter of the Association for Computational Linguistics, pages 645–653, Avignon, France, April 23 - 27 2012. c⃝2012 Association for Computational Linguistics Smart Paradigms and the Predictability and Complexity of Inflectional Morphology Gr´egoire D´etrez and Aarne Ranta Department of Computer Science and Engineering Chalmers University of Technology and University of Gothenburg Abstract Morphological lexica are often imple- mented on top of morphological paradigms, corresponding to different ways of building the full inflection table of a word. Compu- tationally precise lexica may use hundreds of paradigms, and it can be hard for a lex- icographer to choose among them. To au- tomate this task, this paper introduces the notion of a smart paradigm. It is a meta- paradigm, which inspects the base form and tries to infer which low-level paradigm ap- plies. If the result is uncertain, more forms are given for discrimination. The number of forms needed in average is a measure of predictability of an inflection system. The overall complexity of the system also has to take into account the code size of the paradigms definition itself. This pa- per evaluates the smart paradigms imple- mented in the open-source GF Resource Grammar Library. Predictability and com- plexity are estimated for four different lan- guages: English, French, Swedish, and Finnish. The main result is that predictabil- ity does not decrease when the complex- ity of morphology grows, which means that smart paradigms provide an efficient tool for the manual construction and/or auto- matically bootstrapping of lexica. 1 Introduction Paradigms are a cornerstone of grammars in the European tradition. A classical Latin grammar has five paradigms for nouns (“declensions”) and four for verbs (“conjugations”). The modern ref- erence on French verbs, Bescherelle (Bescherelle, 1997), has 88 paradigms for verbs. Swedish grammars traditionally have, like Latin, five paradigms for nouns and four for verbs, but a modern computational account (Hellberg, 1978), aiming for more precision, has 235 paradigms for Swedish. Mathematically, a paradigm is a function that produces inflection tables. Its argument is a word string (either a dictionary form or a stem), and its value is an n-tuple of strings (the word forms): P : String → Stringn We assume that the exponent n is determined by the language and the part of speech. For instance, English verbs might have n = 5 (for sing, sings, sang, sung, singing), whereas for French verbs in Bescherelle, n = 51. We assume the tuples to be ordered, so that for instance the French sec- ond person singular present subjunctive is always found at position 17. In this way, word-paradigm pairs can be easily converted to morphogical lex- ica and to transducers that map form descriptions to surface forms and back. A properly designed set of paradigms permits a compact representation of a lexicon and a user-friendly way to extend it. Different paradigm systems may have different numbers of paradigms. There are two reasons for this. One is that traditional paradigms often in fact require more arguments …

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