Morphological Productivity in the Lexicon

! MORPHOLOGICAL PRODUCTIVITY IN THE LEXICON Onur T. ~ehito~lu and H. Cem Bozsahin Laboratory for the Computational Studies of Language Department of Computer Engineering Middle East Technical University, Ankara, Turkey {onur, bozsahin}@LcsL, metu. edu. tr Abstract In this paper we outline a lexical organization for Turkish that makes use of lexical rules for inflec- tions, derivations, and lexical category changes to control the proliferation of lexical entries. Lexical rules handle changes in grammatical roles, enforce type constraints, and control the mapping of sub- categorization frames in valency changing operations. A lexical inheritance hierarchy facilitates the enforcement of type constraints. Semantic compositions in inflections and derivations are constrained by the properties of the terms and predicates. The design has been tested as part of a HPSG grammar for Turkish. In terms of performance, run-time execution of the rules seems to be a far better alternative than pre-compilation. The latter causes exponential growth in the lexicon due to intensive use of inflections and derivations in Turkish. 1 Introduction Languages like Finnish, Hungarian, and Turkish have relatively rich morphology which governs grammatical functions often delegated to syntax in languages such as English. Prominence of morphology puts a greater demand on the information in the lexicon, which may grow to an unmanageable size due to heavy use of inflections and derivations. In Turkish, for instance, the nominal paradigm has three affixes (number, case, relativizer), and the verbal paradigm has eight (for voice, tense, person, aspect, and mood). Generating the full paradigm for a nominal and a verbal root requires 2 3 and 2 8 entries in the lexicon, respectively. The problem is further complicated by the rich inventory of derivational affixes for both paradigms, as exemplified in 11 Hankamer [7] argues convincingly that full listing of every word form in the lexicon is untenable for agglutinative languages. (1) Yaz-tct-lar-a gOr-ev-ler-i bil-dir-il-me-mipti write-VtoN-PLU-DAT able-VtoN-PLU-ACC know-CAUS-PASS-NEG-ASP-TENSE 'The clerks have not been informed of their duties' Handling inflections and derivations with lexical rules opens us possibilities for encoding semantic and grammatical changes in the lexicon as well. For instance, a causative suffix will demote an agent to a patient or a recipient, and it will add a new grammatical role for the causer (the new agent). A locative case suffix will mark a NP as an adjunct, which can no longer satisfy subcategorization requirements of the verbs or postpositions. We elaborate on the consequences of these phenomena in section 3. Another source for economy of representation can be seen in example (2), where attributive adjectives are used as nouns in 2b and 2d. One solution to this problem is syntactic underspecification, e.g., grouping the 105 nouns and adjectives under a single lexical category. 1 An alternative is to use a lexical rule for differentiating predicate and term reading of the lexical entry. (2) a. kuru yaprak dry leaf 'dry leaf' b. meyve kuru-su fruit dry-POSS 'dried fruit' c. ya#-h hantm age-ADJ lady 'old lady' d. biitiin ya#-h-lar all age-ADJ-PLU 'all elderly' In what follows, we will describe …

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