Verb Semantics and Lexical Selection

VERB SEMANTICS AND LEXICAL SELECTION Zhibiao Wu Department of Information System & Computer Science National University of Singapore Republic of Singapore, 0511 wuzhibia@iscs.nus.sg Martha Palmer Department of Computer and Information Science University of Pennsylvania Philadelphia, PA 19104-6389 mpalmer@linc.cis.upenn.edu Abstract This paper will focus on the semantic representa- tion of verbs in computer systems and its impact on lexical selection problems in machine transla- tion (MT). Two groups of English and Chinese verbs are examined to show that lexical selec- tion must be based on interpretation of the sen- tence as well as selection restrictions placed on the verb arguments. A novel representation scheme is suggested, and is compared to representations with selection restrictions used in transfer-based MT. We see our approach as closely aligned with knowledge-based MT approaches (KBMT), and as a separate component that could be incorporated into existing systems. Examples and experimental results will show that, using this scheme, inexact matches can achieve correct lexical selection. Introduction The task of lexical selection in machine transla- tion (MT) is choosing the target lexical item which most closely carries the same meaning as the cor- responding item in the source text. Information sources that support this decision making process are the source text, dictionaries, and knowledge bases in MT systems. In the early direct replace- ment approaches, very little data was used for verb selection. The source verb was directly replaced by a target verb with the help of a bilingual dictio- nary. In transfer-based approaches, more informa- tion is involved in the verb selection process. In particular, the verb argument structure is used for selecting the target verb. This requires that each translation verb pair and the selection restrictions on the verb arguments be exhaustively listed in the bilingual dictionary. In this way, a verb sense is defined with a target verb and a set of selection restrictions on its arguments. Our questions are: Is the exhaustive listing of translation verb pairs feasible? Is this verb representation scheme suffi- cient for solving the verb selection problem? Our study of a particular MT system shows that when English verbs are translated into Chinese, it is dif- ficult to achieve large coverage by listing transla- tion pairs. We will show that a set of rigid se- lection restrictions on verb arguments can at best define a default situation for the verb usage. The translations from English verbs to Chinese verb compounds that we present here provide evidence of the reference to the context and to a fine-grained level of semantic representation. Therefore, we propose a novel verb semantic representation that defines each verb by a set of concepts in differ- ent conceptual domains. Based on this conceptual representation, a similarity measure can be defined that allows correct lexical choice to be achieved, even when there is no exact lexical match from the source language to the target language. We see this approach as compatible with other interlingua verb representation methods, such as verb representations in KBMT (Nirenburg,1992) and UNITRAN (Dorr, 1990). …

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