Ambiguity Resolution for Machine Translation of Telegraphic Messages

Ambiguity Resolution for Machine Translation of Telegraphic Messages I Young-Suk Lee Lincoln Laboratory MIT Lexington, MA 02173 USA ysl@sst. II. mit. edu Clifford Weinstein Lincoln Laboratory MIT Lexington, MA 02173 USA cj w©sst, ll. mit. edu Stephanie Seneff SLS, LCS MIT Cambridge, MA 02139 USA seneff~lcs, mit. edu Dinesh Tummala Lincoln Laboratory MIT Lexington, MA 02173 USA tummala©sst. II. mit. edu Abstract Telegraphic messages with numerous instances of omis- sion pose a new challenge to parsing in that a sen- tence with omission causes a higher degree of ambi6u- ity than a sentence without omission. Misparsing re- duced by omissions has a far-reaching consequence in machine translation. Namely, a misparse of the input often leads to a translation into the target language which has incoherent meaning in the given context. This is more frequently the case if the structures of the source and target languages are quite different, as in English and Korean. Thus, the question of how we parse telegraphic messages accurately and efficiently becomes a critical issue in machine translation. In this paper we describe a technical solution for the issue, and reSent the performance evaluation of a machine trans- tion system on telegraphic messages before and after adopting the proposed solution. The solution lies in a grammar design in which lexicalized grammar rules defined in terms of semantic categories and syntactic rules defined in terms of part-of-speech are utilized to- ether. The proposed grammar achieves a higher pars- g coverage without increasing the amount of ambigu- ity/misparsing when compared with a purely lexical- ized semantic grammar, and achieves a lower degree of. ambiguity/misparses without, decreasing the pars- mg coverage when compared with a purely syntactic grammar. 1 Introduction Achieving the goal of producing high quality machine transla- tion output is hindered by lexica] and syntactic ambiguity of the input sentences. Lexical ambiguity may be greatly reduced by limiting the domain to be translated. However, the same is not generally true for syntactic ambiguity. In particular, telegraphic messages, such as military operations reports, pose a new chal- lenge to parsing in that frequently occurring ellipses in the cor- pus induce a h{gher degree of syntactic ambiguity than for text written in "~rammatical" English. Misparsing triggered by the ambiguity ot the input sentence often leads to a mistranslation in a machine translation system. Therefore, the issue becomes how to parse tele.graphic messages accurately and efficiently to produce high quahty translation output. In general the syntactic ambiguity of an input text may be greatly reduced by introducing semantic categories in the gram- mar to capture the co-occurrence restrictions of the input string. In addition, ambiguity introduced by omission can be reduced by lexicalizing grammar rules to delimit the lexical items which 1This work was sponsored by the Defense Advanced Research Projects Agency. Opinions, interpretations, conclusions, and rec- ommendations are those of the authors and are not necessarily endorsed by the United States Air Force. ~yrP iCally occur in phrases with omission in the given domain. A awback of this approach, …

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