On Reversing the Generation Process in Optimality Theory

On Reversing the Generation Process in Optimality Theory J. Eric Fosler U.C. Berkeley and International Computer Science Institute 1947 Center Street, Suite 600, Berkeley, CA 94704 fosler~icsi.berkeley.edu Abstract Optimality Theory, a constraint-based phonol- ogy and morphology paradigm, has allowed linguists to make elegant analyses of many phenomena, including infixation and redupli- cation. In this work-in-progress, we build on the work of Ellison (1994) to investigate the possibility of using OT as a parsing tool that derives underlying forms from surface forms. a. Derivational Phonology b. Optimality Theory Figure I: Search Spaces Within Different Paradigms 1 Introduction Optimality Theory (Prince and Smolensky, 1993) is a constraint-based phonological and morphological system that allows violable constraints in deriving output sur- face forms from underlying forms. In OT a system of constraints selects an "optimal" surface output from a set of candidates. The methodology allows succinct anal- yses of phenomena such as infixation and reduplication that were difficult to describe under sets of transforma- tional rules. Several computational methods for OT have been pro- duced within the short amount of time since Prince and Smolensky's paper (Ellison, 1994; Tesar, 1995; Ham- mond, 1995). These systems were designed as genera- tion systems, deriving surface forms from an underlying lexicon. There have, however, been no computational models of OT parsers that derive underlying forms from the surface form. z In this work, we lay the theoretical groundwork for using OT as a parsing tool. 2 Comparing Derivational Methods to Optimality Theory In traditional computational phonology/morphology systems such as two-level phonology (Koskenniemi, 1983), grammars that generate surface forms axe invert- ible, allowing parsing back into underlying forms. In a derivational framework, the grammar converts underly- ing forms to surface outputs via transformations; the in- put and output share the same space (Figure la). In the one-level version of OT that most computational meth- ods use, the space is populated with candidate outputs I Some of the computational work in OT confusingly uses the term "parsing" to refer to generation. created by a generator function GZN operating on in- put strings. The search narrows in on an optimal out- put (Figure lb) using evaluation constraints in a process called EVAL; successively smaller boundaries are cut out by the constraints until only one candidate remains. It is easy to see why the derivational method can be run backward: it just retraces derivational links in the graph. It is not obvious, though, how the input can be found from the search space in OT. 3 Tagalog Infixation Infixation has traditionally been a difficult problem for computational models that use two-level phonology (Sproat, 1992). Infixation in Tagalog, however, has been modeled using OT (McCarthy and Prince, 1995). In Tagalog, the urn affix can appear as a prefix, or "move" slightly into the word to which it is attaching (French, 1988). Root with um Gloss alis um-alis "leave" sulat s-um-ulat "write" gradwet gr-um-adwet "graduate" McCarthy and Prince analyze um as a prefix, which moves into a word to reduce the number of …

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