Word Alignment Annotation in a Japanese-Chinese Parallel Corpus
Yujie Zhang, Zhulong Wang, Kiyotaka Uchimoto, Qing Ma, Hitoshi Isahara
National Institute of Information and Communications Technology
3-5 Hikaridai, Seika-cho, Soraku-gun, Kyoto, Japan, 619-0289
E-mail: {yujie.zhang, uchimoto, isahara} @nict.go.jp, wangzhulong@cn.fujitsu.com, qma@math.ryukoku.ac.jp

Abstract
Parallel corpora are critical resources for machine translation research and development since parallel corpora contain translationequivalences of various granularities. Manual annotation of word alignment is of significance to provide gold-standard for developing
and evaluating both example-based machine translation model and statistical machine translation model. This paper presents the workof word alignment annotation in the NICT Japanese-Chinese parallel corpus, which is constructed at the National Institute ofInformation and Communications Technology (NICT). We describe the specification of word alignment annotation and the tools
specially developed for the manual annotation. The manual annotation on 17,000 sentence pairs has been completed. We examined themanually annotated word alignment data and extracted translation knowledge from the word aligned corpus.

1.

Introduction

Parallel corpora contain translation equivalences ofvarious granularities and therefore are critical resources
for machine translation research and development.
Manual annotation of word alignment is of significancefor providing gold-standard to development andevaluation of both example-based machine translation
model and statistical machine translation model. Because
parallel corpora of Asian languages are less developed,
theNationalInstituteofInformation
andCommunications Technology (NICT) started amultilingual corpora construction project in 2002, which
is focused on Asian language pairs (Uchimoto et al.,2004). The project makes effort on the annotation ofdetailed information, including syntactic structure andalignment at word & phrase levels. We call the corpora theNICT Multilingual Corpora.
This paper presents the word alignment annotation in
the Japanese-Chinese parallel corpus, one parallel corpusof the NICT Multilingual Corpora. We will describe thespecification for manual annotation and the tools
specially developed for the manual annotation. The
experience we obtained and points we paid special
attentions are also introduced for share with otherresearches who are engaged in parallel corpora
construction. To the best of our knowledge, the corpus is
the first Japanese-Chinese parallel corpus annotated withthe detailed information in the world. It will provide
materials for investigation into the characteristic oftranslation from Japanese to Chinese.

2.

NICT Japanese-Chinese Parallel Corpus

The NICT Japanese-Chinese parallel corpus consists of
the original Japanese text and its Chinese translations(Zhang et al., 2005-a). The original data is fromnewspaper articles or journals, such as Mainichi
Newspaper in Japanese. The original articles weretranslated by skilled translators. In human translation, thearticles of one domain were all assigned to the sametranslator to maintain consistency of terminology inChinese. The Chinese translations were then revised byother translators and lastly revised by Chinese natives.
Each article was translated one sentence to one sentence,
so the obtained parallel corpus is already sentence aligned.
In Japanese side, morphological and syntactic structure
information has been annotated following thespecification of the Corpus of Spontaneous Japanese(Maekawa et al., 2000). In Chinese side, word
segmentations and parts-of-speech have been annotatedfollowing the specification of Peking University (Yu,1997). The detail of the corpus is listed in Table 1.
Japanese
ChineseSentences
38,383
Words
947,066
877,859
Vocabulary
36,65733,425Singletons
15,036
13,238
Aver. Sentence
24.7
22.9
lengthTable 1. Characteristics of NICT Japanese-Chinese
Parallel Corpus.

3.

Tool for Word Alignment Annotation

We specially designed and developed a tool for manual
annotation of word alignment based on the investigation
into a few work of word alignment annotation (Melamed,2001; LDC, 2006). Our motivation is as follows. (a) Since
automatic alignment technologies are applicable, theannotation here is manual revision on the automaticallyobtained alignments. A multi-aligner developed by(Zhang et al. 2005-b) is used in this work. The multialigner consists of a lexical knowledge based aligner,
Chinese to Japanese direction application of GIZA++ andJapanese to Chinese direction application of GIZA++(Och & Ney, 2000 ). The evaluation of the multi-aligner
showed that 63% recall rate and 79% precision have beenachieved. In order to use the results of the multi-aligner,
the tool should be able to display the results of the multi-1025

aligner. (b) The tool should be able to provide a visualizedinterface for annotators to easily revise the automaticallyobtained results. (c) The tool should be able to display
larger syntactic granularities in addition to words whensyntactic structure information is available. In this way,

annotators may select larger syntactic granularities andthen align them effectively and conveniently. So thetranslation equivalences between larger units or between
syntactic structures can be annotated through this tool.

Figure 1. Visualized interface of the tool for manual alignment annotation (word level).

Figure 2. Visualized interface of the tool for manual alignment annotation (phrase level).

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3.1 Visualized Interface
The visualized interface of our tool is showed in Figure 1and Figure 2.
In Figure 1, the left area is used to display the ID list of
the input sentence pairs. On the right, the upper area andthe lower area are used to display the syntactic structuresof Chinese sentence and Japanese sentence, respectively.
The middle area is operation area where alignments aredisplayed and are to be revised. Each word of both
Chinese sentence and the Japanese sentence is displayedin one quadrilateral button separately. Annotators click
the buttons to select words for annotation. The lines
connecting the Chinese words and the Japanese words
mean alignments between them. The lines of differentalignments are displayed in different colour. The
quadrilateral buttons of the unaligned words are displayedin yellow, while ones of the aligned ones are displayed ingrey. After one word is selected and aligned, the colour ofthe quadrilateral button will be changed from yellow togrey.
For labeling one alignment, annotators select Chinese(Japanese) words and then the corresponding words in theJapanese (Chinese) side by clicking the left button of themouse. After the click operations, the selected Chinese
words and the Japanese words are linked by lines. If thealignment is one-to-one, there is one line between them. If
the alignment is many-to-many, i.e. multiple Chinese
words being aligned to multiple Japanese words, the lines
from each word of both the Chinese side and the Japaneseside are got together at the same point, which is located at
the middle area. See the 2-to-5 alignment in Figure 1, “不仅…也-to-ばかり で は なく…も”(not only …
but). This presentation is different from the tool proposedby (Melamed, 2001), where each word of the group of theone side is linked to each word of the group on anotherside and therefore too many lines look redundancy.

Strictly speaking, the correspondences between two
groups of words do not mean each word of one groupcorrespond to every word of another group. In our tool,
the lines from each word of one group are got together at
one point first and then from the point the lines areradiated to each word of another group. One-to-many andmany-to-one alignments are the special cases ofmany-to-many alignments.
For adding one word to an alignment, just click theword and then click any word or line of the alignment. For
deleting one word from one alignment, just click the word.
Then the corresponding line will disappear.
If phrase alignment mode is selected, the quadrilateralbuttons of phrase will be displayed in the middle area. At
present, only Japanese sentences have syntactic structure
information. As shown in Figure 2, words of each phrase
are contained in a larger quadrilateral button. Annotators
can click the quadrilateral button to select phrases forannotation. In this way, larger units can be considered andtherefore be annotated more effectively.

3.2 Data Structure
We store the alignment data in a XML file and encode
them in Unicode. The following tags are designed for
different types of data.
<srctext> Chinese sentence<srcword> Chinese word sequence with Part of Speech<tgttext> Japanese sentence<tgtword> Japanese word sequence with Part of Speech;<wordalignment_1> automatically aligned result<srctree> syntactic structure of the Chinese sentence<tgttree> syntactic structure of the Japanese sentence<wordalignment_2> manually annotated word alignment<structalignment> manually annotated phrase alignment.
The alignment data of the example displayed in Figure 1
is shown in Figure 3.

Figure 3. The illustration of the data structure.

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4.

Specification for Manual Word
Alignment Annotation

In alignment annotation, the semantic equivalences
between Chinese words and Japanese words are detected
and are aligned. The annotation is carried out according tothe following criteria.
(1) Content words are considered first. After all content
words are aligned, the left words are processed.
(2) The semantic equivalences should be approved
based on a few pre-specified Japanese-Chinese translation
dictionaries. The translation dictionaries are used toqualify the annotation of semantic equivalences in order
to avoid annotation of free translations, whose semantic
equivalences only appear in the certain sentence pairs andtherefore are not applicable in other case. In wordalignment annotation, we only consider semantic
equivalences that will be applicable in general. We willdeal with free translations in phrase level alignment.
(3) Alignment unit should be the minimum granularity,i.e. the smallest number of words. The words within one
unit should correlate each other in semantics and therefore
can not be separated further. This criterion aims atincreasing the coverage of the translation knowledge thatwill be extracted from the aligned corpus.
(4) In the case of idioms and frozen expressions, thelarger units should be preferred on both sides to ensure thetwo groups to be equivalent semantically andgrammatically.
(5) For some Japanese postpositions, the counterpart in
Chinese usually consists of one preposition and one suffix,appearing discontinuously. For instance, in the Japanesepostposition phrase “机の上で(on the table) ” and its
Chinese translation“在 桌子 上(on the table)”, Japanesepostposition “ で (on) ” corresponds to the Chinesepreposition “在(on)” and the suffix “上(on)”. The
Chinese preposition “在(on)” and the suffix “上(on)”should be glued together first and then aligned to theJapanese postposition “で(on)” .
(6) For some Japanese conjunctions, the counterpart in
Chinese usually consists of two conjunctions, appearing
discontinuously. For instance, in the Japanese subsentence “遅いが” (it is late, but) and its Chinesetranslation “虽然晚了，但是 (it is late, but)”, theJapanese conjunction “が (but)” corresponds to theChinese conjunction “虽然 (but)” and “但是 (but)”.
The separated two Chinese conjunctions“虽然 (but)”and“但是 (but)” should be glued together first and thenaligned to the Japanese conjunction “が (but)”.
(7) One big difference between Japanese and Chinese
language is that the former has inflectional morphology
but the latter has not. In Chinese, the words such as “了(past tense particle)”,“过 (perfect aspect particle)” and“着 (progressive aspect particle)” are used to express
tense and aspect, “被 (by)” are used to express passivevoice, “使 (causative morpheme)”are used to express
causative aspect. If the Japanese inflection suffix issegmented from its root, i.e. appearing as one independentmorpheme, the Chinese particle should be aligned to thesuffix. Otherwise, the Chinese particle should be glued toits main verb first and then aligned to the Japanese verb,
which consists of the root and the inflection suffix. Whenthe subject of the active sentence appears in the passive
sentence, in Japanese it is expressed as“SUBJECT に (bySUBJECT)” and in Chinese it is expressed as “被SUBJECT (by SUBJECT)”. In this case, the Chinese
word“被 (by)”is aligned to the Japanese word“に (by)”.

5.

What are Extracted from the Annotated
CorpusThe manual annotation of word and phrase alignment on
17,000 sentence pairs has been completed. We examined
the manually annotated data and extracted translation
knowledge from them. From the word alignment data, atranslation dictionary is obtained which may be usedwithout restriction on context. From the phrase alignment
data, the translation templates are obtained, in which
context restrictions are contained. The former knowledge
aims at increasing the coverage of applying the translation
knowledge, while the later aims at increasing the accuracyof applying the translation knowledge. Some examples ofthe extracted knowledge are shown in Figure 4 and Figure
5. Figure 4 shows the examples of the obtained semanticequivalences at phrase level. Figure 5 shows the examplesof the obtained translation templates which are obtainedby replacing the specified aligned words, displayed inparentheses, with variables, like X1.

Figure 4. Examples of the obtained semantic equivalencesat phrase level.

Figure 5. Examples of the obtained translation templates.

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6.

Conclusion

This paper presents word and phrase alignment
annotation in the NICT Japanese-Chinese parallel corpus.
A visualized tool is developed to assistant the manualannotation. The data structure and the general guideline
are described. The translation knowledge extracted fromthe aligned corpus is also reported. At present eachsentence pair is annotated by only one annotator. We plan
to select a small part of sentence pairs and ask different
annotators to annotate alignment on them, in order toexamine divergence among different annotators.

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