Extending Kimmo’s Two-Level Model of Morphology

EXTENDING KIMMO'S TWO-LEVEL MODEL OF MORPHOLOGY * Anoop Sarkar Centre for Development of Advanced Computing Pune University Campus, Pune 411007, India anoop~parcom.ernet.in Abstract This paper describes the problems faced while us- ing Kimmo's two-level model to describe certain Indian languages such as Tamil and Hindi. The two-level model is shown to be descriptively inad- equate to address these problems. A simple ex- tension to the basic two-level model is introduced which allows conflicting phonological rules to co- exist. The computational complexity of the exten- sion is the same as Kimmo's two-level model. INTRODUCTION Kimmo Koskenniemi's two-level model (Kosken- niemi, 1983, Koskenniemi, 1984) uses finite-state transducers to implement phonological rules. This paper presents the experience of attempting a two- level phonology for certain Indian languages; the problems faced in this attempt and their resolu- tion. The languages we consider are Tamil and Hindi. For the languages considered we want to show that practical descriptions of their morphol- ogy can be achieved by a simple generalization of the two-level model. Although the basic two-level model has been generalized in this paper, the ex- tensions do not affect the complexity or the basic tenets of the two-level model. SOME PROBLEMS FOR THE TWO-LEVEL MODEL The two-level model is descriptively adequate for most morphological processes occuring in Indian languages. However, there are some cases where the basic two-level fails to give an adequate de- scription. One problem is caused by the large number of words imported from Sanskrit in lan- guages such as Hindi, Tamil and Tibetan. The other problem occurs in Tamil where phonology disambiguates between different senses of a mor- pheme. The cases where these occur is common *I would like to thank P. Ramanujan and R. Doctor for their help, and Dr. Darbari for his support. and productive. They cannot be considered as ex- ceptional. For example, in Tamil the verb 1;ula£ (to be similar) is derived from the Sanskrit base word tula (similarity). The past participle of tulai exhibits the following property. (LR and SR refer to the lexical and surface environments respectively). (i) LR: tulai+Ota SR: tolaiOtta (adj. who resembles [something]) In this example, the consonant insertion at the morpheme boundary is consistent with Tamil phonology, but the realization of u as o in the en- vironment of tu follows a morphology that origi- nates in Sanskrit and which causes inconsistency when used as a general rule in Tamil. The follow- ing example illustrates how regular Tamil phonol- ogy works. (2) LR: kudi+Ota SR: kudiOtta (adj. drunk) (3) LR: tolai+0ta SR: tolaiOtta (adj. who has lost [something]) From examples (1) through (3) we see that the same environment gives differing surface realiza- tions. Phonological rules formulated within the two-level model to describe this data have to be mutually exclusive. As all phonological rules are applied simultaneously, the two-level model can describe the above data only with the use of arbi- trary diacritics in the lexical representation. The same problem occurs in Hindi. In Table 1 (6) and (7) follow …

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