To what extent does case contribute to verb sense disambiguation?

Word sense disambugation has recently been utilized in corpus-based aI)proaches, reflecting the growth in the number of nmehine readable texts. One (:ategory ()f al)l)roa(:hes disambiguates an input verb sense based on the similarity t)etween its governing (:its(; fillers and those in given examl)les. In this palter , we introdu<:c the degree of (:based apl)roach ill exl)laining its effe.etivity for verb sense disamibiguation in Japanese. A representative example-based method for verb sense disambiguation was proposed by Kurohashi and Nagao (Kurohashi's inethod) (Kurohashi rand Nagao, 1994). Their method uses an 0,xamph; database, containing examples of collocations as in figure 1. Figure 1 shows a fragment of tim entry associated wittl the Japan(;se verb to'ru. As with most words, the ve, rb to'r"¢t has multipie senses, examples of whit:h are "to take/steal," "to attain," "to subst'ril)e" and "to reserve," The database gives one or more case frame(s) associated with tilt', verbs for each of their senses. In .Japanese, a coutI)lelnt;nt Of a verb, which is a constituent of the case frame of the verb, consists of a nonii phrase (case filler) followed by a case marker such ms ga (nominative) or o (accusative). The database has ~m example set of case fillers for each case. As shown in figure 1, examples of a comi)lement c.an be considered as an extensional description of the selectional restriction on it. The task (:onside.red in this paper is %o interpret" a verb in an input s('.ntcnt:e, i.e. to choose ()lit) sense from a set of candidate senses of the verb. Given an input sentence, Kurohashi's method interprets the verb in the input by computing semantic similarity between the input and exalnples. For this computation, Kurohashi 's nmthod experimeIltally uses the Ja,panese word thesaurus Bunruigoihyo (National-Language R(> search Institute, 1964). As with Inost thesauruses, the length of the 1lath between two words in Bunr'uigoihyo is exl)e, eted tt) reflect the similarity be,tween them. Figure 2 ilhlstrates a fragment of B'unruigoihyo in(:hlding some of the nouns in figure 1. I,et us take the example sentence (1). (1) hisho .qa sh, indaish, a o tor,u. (set:retm'y-NOM) (siegel,trig (:ar-ACC) (?) lit this examph',, it may t)e judged according to tigure 2 that h, ish, o ("secretary") and shindaisha ("sleeping c a r " ) i n (1)i~l(, ,'~emantically similar to joshu ("assistant") att(l hikbki ("airplane"), reSl)ectively, which are cxamI)les that collocate with t(rru ("to reserve"). As sut'h, the sense of rot'u, in (1) can be interpreted as "to reserve." llowever, in Kurohashi's nmthod, several usefifl properties for verb disambuguatittn are missing: 1. httuitively speaking, the, contribution of the