Back Transliteration from Japanese to English using Target English Context

Back Transliteration from Japanese to English Using Target English Context Isao Goto†, Naoto Kato††, Terumasa Ehara†††, and Hideki Tanaka† †NHK Science and Technical Research Laboratories 1-11-10 Kinuta, Setagaya, Tokyo, 157-8510, Japan goto.i-es@nhk.or.jp tanaka.h-ja@nhk.or.jp ††ATR Spoken Language Trans- lation Research Laboratories 2-2-2 Hikaridai, Keihanna Science City, Kyoto, 619-0288, Japan naoto.kato@atr.jp †††Tokyo University of Science, Suwa 5000-1, Toyohira, Chino, Nagano, 391-0292, Japan eharate@rs.suwa.tus. ac.jp Abstract This paper proposes a method of automatic back transliteration of proper nouns, in which a Japanese transliterated-word is restored to the original English word. The English words are created from a sequence of letters; thus our method can create new English words that are not registered in dictionaries or English word lists. When a katakana character is con- verted into English letters, there are various candidates of alphabetic characters. To ensure adequate conversion, the proposed method uses a target English context to calculate the probability of an English character or string corresponding to a Japanese katakana charac- ter or string. We confirmed the effectiveness of using the target English context by an ex- periment of personal-name back translitera- tion. 1 Introduction In transliteration, a word in one language is con- verted into a character string of another language expressing how it is pronounced. In the case of transliteration into Japanese, special characters called katakana are used to show how a word is pronounced. For example, a personal name and its transliterated word are shown below. Cunningham カニンガム (ka ni n ga mu) [Transliteration] Here, the italic alphabets are romanized Japanese katakana characters. New transliterated words such as personal names or technical terms in katakana are not al- ways listed in dictionaries. It would be useful for cross-language information retrieval if these words could be automatically restored to the original English words. Back transliteration is the process of restoring transliterated words to the original English words. Here is a problem of back transliteration. ? クラッチフィールド (English word) (ku ra cchi fi – ru do) [Back transliteration] There are many ambiguities to restoring a transliterated katakana word to its original Eng- lish word. For example, should "a" in "ku ra cchi fi – ru do" be converted into the English letter of "a" or "u" or some other letter or string? Trying to resolve the ambiguity is a difficult problem, which means that back transliteration to the cor- rect English word is also difficult. Using the pronunciation of a dictionary or lim- iting output English words to a particular English word list prepared in advance can simplify the problem of back transliteration. However, these methods cannot produce a new English word that is not registered in a dictionary or an English word list. Transliterated words are mainly proper nouns and technical terms, and such words are often not registered. Thus, a back transliteration framework for creating new words would be very useful. A number of back transliteration methods for selecting English words from an English pronun- ciation dictionary have been proposed. They in- clude Japanese-to-English (Knight and Graehl, 1998) …

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