Hoa Trang Dang , Karin Kipper

In this paper we specifically address questions of polysemy with respect to verbs, and how regular extensions of meaning can be achieved through the adjunction of particular syntactic phrases. We see verb classes as the key to making generalizations about regular extensions of meaning. Current approaches to English classification, Levin classes and WordNet, have limitations in their applicability that impede their utility as general classification schemes. We present a refinement of Levin classes, intersective sets, which are a more fine-grained classification and have more coherent sets of syntactic frames and associated semantic components. Wc have preliminary indications that the membership of our intersective sets will be more compatible with WordNct than the original Levin classes. We also have begun to examine related classes in Portuguese, and find that these verbs demonstrate similarly coherent syntactic and semantic properties. 1 I n t r o d u c t i o n The difficulty of achieving adequate handcrafted semantic representations has limited the field of natural language processing to applications that can be contained within well-defined subdomains. The only escape from this limitation will be through the use of automated or semi-automated methods of lexical acquisition. However, the field has yet to develop a clear consensus on guidelines for a computational lexicon that could provide a springboard for such methods, although attempts are being made (Pustejovsky, 1991), (Copestake and Sanfilippo, 1993), (Lowe et al., 1997), (Dorr, 1997). The authors would like to acknowledge the support of DARPA graat N66001-94C-6043, ARO grant DAAH04-94G-0426, and CAPES grant 0914/95-2. One of the most controversial areas has to do with polysemy. What constitutes a clear separation into senses for any one verb, and how can these senses be computationally characterized and distinguished? The answer to this question is the key to breaking the bottleneck of semantic representation that is currently the single greatest limitation on the general application of natural language processing techniques. In this paper we specifically address questions of polyscmy with respect to verbs, and how regular extensions of meaning can be achieved through the adjunction of particular syntactic phrases. We base these regular extensions on a fine-grained variation on Levin classes, intersective Levin classes, as a source of semantic components associated with specific adjuncts. Wc also examine similar classes in Portuguese, and the predictive powers of alternations in this language with respect to the same semantic components. The difficulty of determining a suitable lcxical representation becomes multiplied when more than one language is involved and attempts are made to map between them. Preliminary investigations have indicated that a straightforward translation of Levin classes into other languages is not feasible (Jones et al., 1994), (Nomura et al., 1994), (Saint-Dizier, 1996). However, we have found interesting parallels in how Portuguese and English treat regular sense extensions.