A Constraint-Based Approach to Korean Verb Inflections
Jong‐Bok Kim · Waseda University Repository (Waseda University) · 1993
Two mechanisms are adopted in Pollard and Sag (1987) to formalize a more efficient lexicon structure and to eliminate massive in word information, namely hierarchical structures of the lexicon and lexical rules. The hierarchically sorted structures of the lexicon, using the mathematically well-defined notions of subsumption1 and sort2 , greatly reduce the vertical redundancy in the lexical information, caused by encoding in each lexical entry all its linguistic information shared with whole word classes, such as parts of speech, valence, classes, and so forth. On the other hand, lexical rules, mapping one class of words to another, eliminate the massive horizontal redundancy' that comes from groups of words whose specific information contents are correlated according to recurrent patterns, such as in inflectional and derivational paradigms. These lexical rules from a declarative perspective capture generalizations about relationships between members of two or more word classes. And from a procedural point of view, they describe processes that produce an output lexical entry from an input. The adoption of lexical rules with sortal hierarchies raises the question of where word formation occurs within or outside the lexicon. As pointed out by Krieger and Nerbonne (1991), the lexical rule approach assumes that word formation takes place without the lexicon, in the sense that the form of lexical rules is not identical to the structure of general lexical entries. A lexical rule is not a feature structure itself, but the relation between two lexical entries, i.e., in HPSG between two feature structure descriptions. Feature structures in HPSG are always sorted, and these sorts are partially ordered via subsumption. However, this isn't true of lexical rules, as noted in Krieger and Nerbonne (1991). A lexical rule does not have a sort and there is no way to relate it to other feature structures. If we assume that a lexical rule can be sorted and resides in the lexicon, this sort ought to be a subsort of lexical-sign according to Pollard and Sag (1987). However, in Pollard and Sag (1987), they are not its subsorts, and just reside in the lexicon as a different component. The basic purpose of this paper is to propose an approach that incorporates lexical rules into the lexicon, and place them under sortal hierarchies: Both reduandancies will be reduced by hierarchical lexical structures in our system. We will eliminate lexical rules for Korean verb inflection and define them as information bearing objects, indistinguishable in their form and meaning from other lexical entries. This goal will be achieved by defining local constraints on each well-defined and hierarchically sorted stem. Such a declarative and constraint-based approach -to Korean inflections will first obviate the necessities of morphological principles such as how each stem and suffixes are combined, what kind of specific (syntactic, semantic, and pragmatic) information each suffix contributes to the stem it attaches to, and how the information is incremented.