The Fourth Symposium on Natural Language Processing 2000

SIMULTANEOUS JAPANESE-ENGLISH INTERPRETATIONBASED ON EARLY PREDICTION OF ENGLISH VERB
S. Matsubarayx, K. Iwashimaz, N. Kawaguchizx,
K. Toyama?x and Y. Inagaki?

yFaculty of Language and Culture, Nagoya University
zDepartment of Information Engineering, Nagoya University?Department of Computational Science and Engineering, Nagoya University

xCenter for Integrated Acoustic Information Research (CIAIR), Nagoya University
Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan

Simultaneous machine interpretation is one of the most ambitious applications of natural language processing. Incrementality in language translation is an inevitable property in such an application. This paper describes a technique for translating spoken Japanese into spoken English
incrementally. Generally speaking, it is very dicult for a machine translation system to incrementally transfer from Japanese to English because of the di erence in the word-order of them.
To overcome the diculty, the technique utilizes some novel ideas: 1) predicting the verb early, 2)
putting a phrase in another position, 3) changing the voice, 4) controlling the intonation, and 5)
generating a repair expression. According to the technique, the system can generate the corresponding English sentence synchronously with the input of spoken Japanese. An experimental system ofincremental Japanese-English spoken language translation has been made. An experiment on thesystem has shown the technique to be e ective.
Key words: simulatneous interpretation, spoken language translation, incremental interpretation, verb prediction.

INTRODUCTION

Spoken language translation has been an important research topic in recent years.
A cross-lingual speech conversation through a spoken language translation system demands that the system should also engage in the conversation without preventing its
coherence. Our intuitions suggest that the system should behave like an simultaneousinterpreter.
In order to develop a simultaneous interpretating system, working synchronouslywith a spoken language input, a technique for translating natural language incrementally is strongly required [7, 6, 13]. Towards such an ambitious application,some attempts have been recently made so far. Kitano has proposed a technique ofincremental sentence production for modeling simultaneous machine interpretation[8, 9]. As well, Amtrup has introduced chart-based incremental transfer frameworkfor processing head switching in German-English machine translation [1]. Furuseand Iida has developed a technique of incremental translation utilizing transfer patterns [5], and Mima et al. has extended it by introducing simultaneous interpreter's
know-how[14]. Furthermore, Matsubara and Inagaki has achieved ne-grained incrementality 1 in English-Japanese machine translation [10, 11].
One of the points to be considered in developing an incremental spoken languagetranslation system is the di erence in word-order between the source language and thetarget language. Since there exists an inevitable trade-o relation between incrementality and accuracy, the di erence might cause to lose the synchronization between
1 Fine-Grained Incremental Interpretation means that the processor analyses each small part of a sentence, such as each word or morpheme, immediately it is encountered. In contrast, Coarse-Grained Incremental Interpretation occurs if the processor waits until larger chunks of a sentence are encountered [2].

c 2000 The Fourth Symposium on Natural Language Processing

SNLP'2000, Chiang Mai, Thailand

Table 1.

Comparison between Japanese and English

item1) position of the predicate2) exibility of word-order3) interrogative expression4) negative expression5) subjective case ellipses

Japanesearound the end of a sentence
exibleend of a sentenceend of a sentencevery frequent

Englishafter the subject
stricthead of a sentence
after the subject
very few

the input and the output of the system. For example, translation of Japanese into
English causes the system the following problems: Generating English sentences according to the word-order of Japanese sentences,

the system cannot output a correct and understandable translation result (lowquality problem).
 Generating a standard English sentence for a Japanese sentence, the system cannot output the most of the English sentence until the Japanese verb is inputed.
Because the verb in English appears at an early stage though that in Japanese
does at the end of sentences. (low-immediacy problem)

These are fatal to simultaneous machine interpreting between languages which are
di erent in word-order. The above studies, however, have ever given little attention
to them.
In this paper, we describes a technique for translating spoken Japanese into
spoken English incrementally. The technique utilizes ve novel ideas: 1) predicting
the verb early, 2) putting a phrase in another position, 3) changing the voice, 4)
controlling the intonation, and 5) generating a repair expression. According to thetechnique, the system can generate the English sentence synchronously with the inputof spoken Japanese. We have made a prototype system of incremental JapaneseEnglish spoken language translation. The system is composed of four stages: parsing,transfer, generation and prediction. An experiment on the system have made us
con rm the e ectiveness of the technique.
This paper is organized as follows: Section 2 shows the ideas to generate English
incrementally. Section 3 explains the technique for predicting the English verb early.
Section 4 describes an overview of the system. Sections 5 reports on an experimentalresult.
1.

INCREMENTAL ENGLISH GENERATION

Incremental translation means to transfer a source language, according to its appearance order, to a target language. Its feasibility much depends on the degree ofthe di erence in word-order between both languages. Table 1 shows the structural
di erences between Japanese and English. The key to success of exceedingly incremental Japanese-English translation is to overcome the diculty on these di erences.
The following in this section describes the technique for coping with 1),2) and 3) inTable 1.

Simultaneous Japanese-English Interpretation based on Early Prediction of English Verb

1.1. Early Prediction of English Verb
As Table 1 shows, the verb position in Japanese, which is widely di erent fromthat in English, is around the end of a sentence. Therefore, the Japanese verb is notdecided until the Japanese sentence is inputed entirely. For example, in a Japanesesentence:(1) kare-wa(He) Chenmai-e(to Chiengmai) densha-de(by train) iki-mashi-ta(went).
(He went to Chiengmai by train.)

the predicate \iki-mashi-ta" is generated in the end.
However, we may be able to predict the verb using the other components of asentence to some extent. In particular, the improvement of the predictability can beexpected in the limited task domain because the variation of the verbs is restricted.
Predicting the verbs from the noun phrases in an early stage, the system can executes
translation processing with less delay.
1.2. Replacing Word-OrderWe can say that the position of an adverb and an adverbial phrase are exible
to some extent though that in English is usually strict. Therefore, the system might
output the corresponding English immediately with the input of a Japanese adverbialphrase. As an example, let us consider the following simple Japanese sentence:kesa(in this morning) ken-wa(Ken) sanpo-shi-ta(took a walk).
(Ken took a walk in this morning.)(2)

As soon as the adverbial phrase \kesa" is inputed, the system outputs an Englishprepositional phrase \in this morning". We would like to emphasize that an English
sentence(3)

In this morning, Ken took a walk.

is correct and understandable as the translation result of (2).
1.3. Putting Sentences into the Passive
Since the subjective case is omited very frequently in Japanese, the mechanism
to complement it is necessary in order to generate that in English. However, byputting the English sentence into the passive voice, the omited subjective case is
not necessarily translated. Translating the Japanese objective case as the English
subjective case, the system can put o the output of an English verb.
1.4. Using A Rising Intonation
An interrogative phrase usually appears in the head of a sentence in English, like\Do ... ?". On the other hand, that in Japanese appears in the end, like \... ka?". Therefore, the system can not decide whether it is armative or interrogative
until the whole of a Japanese sentence is inputed. In an English conversation, byproducing a sentence with a rising intonation, whether it is interrogative or not canbe indicated with no such the phrase.

SNLP'2000, Chiang Mai, ThailandCoocurrence Data

Dictionary&Grammar

PREDICTION
English Verb

Japanese Input

English Noun Phrase
English Output

TransferRules

GENERATIONJapanese
TRANSFER
Case Structure

EnglishPhrase Structures

PARSING

Figure 1.

Word Concept Dictionary

Con guration of incremental Japanese-English translation system

1.5. Utilizing Repair Expressions
None of the above ideas 1)-4), which can be considered to be e ective for incremental Japanese-English translation, necessarily bring correct results. In this paper,
we regard an incorrect English fragment as a kind of error expressions producedby the system. That is to say, the system makes it correct by generating repair
expressions even if it produces incorrect fragments.
2.

AN OVERVIEW OF THE SYSTEM

Figure 1 shows the con guration of incremental Japanese-English spoken language translation system. The system, which works in a phrase-by-phrase basis, iscomposed of four stages: parsing, transfer, generation and prediction. The parsing stage makes Japanese case structures of inputs for every additional phrase. The
transfer stage makes English phrase structures by applying transfer rules to them [12].
The generation stage outputs English fragments according to an English generation
procedure based on the ideas shown in Section 2.
The prediction stage utilizes all noun phrases in English phrase structures andwork according to the following procedure: 1) conceptualizing the noun phrases
using EDR Word Dictionary [3], and 2) extracting an English verb with the mosthigh frequency in cooccurrence data for ATR Dialogue Database [4].
3.

EXPERIMENT

An experimental system of incremental Japanese-English translation has beendeveloped in GNU Common Lisp 2.2.2 on a Unix workstation. In order to analize
four dialogues whose task are travel application on the telephone in ATR Dialogue
Database [4], we have made a dictionary consisting of 540 words. We have registered
1,883 rules expressing coocurrence relations between noun phrases and verbs concep-

Simultaneous Japanese-English Interpretation based on Early Prediction of English Verb

Table 2.

Experimental result on translation accuracy

itemcorrect

error cause

utterances rate(%)
140
54.1
ellipsis of subject
79
30.5
parsing error
33
12.7
syntactic ambiguity
72.7

incorrect

tualized using EDR Word Dictionary [3] as coocurrence data to predict the English
verb. In the experiment, we have used 259 utterances by Japanese speakers. An
open-test experiment about verb prediction, providing 53.1% of prediction accuracy,shows the technique to be usable for early English verb prediction. Table 2 shows thetranslation results including error causes. The English sentences generated correctly
according to the ideas explained in Section 2 account for 57.1 % of all correct English
sentences, and we can con rm the technique to be e ective.
4.

CONCLUDING REMARKSThis paper has described a technique for translating spoken Japanese into spoken
English incrementally. To overcome the diculty on di erent word-order, the technique utilizes some ideas: 1) predicting the verb early, 2) putting a phrase in anotherposition, 3) changing the voice, 4) controlling the intonation, and 5) generating a
repair expression. According to the technique, an experimental system of incremental Japanese-English spoken language translation has been made. An experiment on
the system has shown the technique to be e ective for incremental Japanese-English
translation which can generate acceptable English sentences.
The current prototype system can cope with only simple and grammatical Japanese
sentences. Complex or ungrammatical sentences, however, appear very frequently inspoken Japanese. We would like to go on to develop a technique for incrementallyparsing of spoken Japanese language.
ACKNOWLEDGMENTS

The authors would like to thank all memebers of ATR Interpreting Telecommunications Research Labs for their useful comments. This paper owes much to thevaluable discussions with Yoshihide Kato, Satoru Asai and Yasuyuki Aizawa. This
work is partially supported by The Hori Information Science Promotion Foundation.
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