Word-level Dependency-structure Annotation
to Corpus of Spontaneous Japanese and Its Application
Kiyotaka Uchimoto∗ and Yasuharu Den†∗

National Institute of Information and Communications Technology
3-5 Hikari-dai, Seika-cho, Soraku-gun, Kyoto 619-0289, Japanuchimoto@nict.go.jp†
Department of Cognitive and Information Sciences, Faculty of Letters, Chiba University
1-33 Yayoicho, Inage-ku, Chiba 263-8522, Japanden@cogsci.l.chiba-u.ac.jp
Abstract
In Japanese, the syntactic structure of a sentence is generally represented by the relationship between phrasal units, bunsetsus in Japanese,
based on a dependency grammar. In many cases, the syntactic structure of a bunsetsu is not considered in syntactic structure annotation.
This paper gives the criteria and definitions of dependency relationships between words in a bunsetsu and their applications. The target
corpus for the word-level dependency annotation is a large spontaneous Japanese-speech corpus, the Corpus of Spontaneous Japanese(CSJ). One application of word-level dependency relationships is to find basic units for constructing accent phrases.

1. Introduction
The Corpus of Spontaneous Japanese (CSJ) (Maekawa etal., 2000) — the largest spontaneous-speech corpus in theworld available to the public — is a collection of monologues and dialogues. It includes transcriptions of speeches
as well as audio recordings. Approximately one tenth of the
CSJ has been manually annotated with information aboutmorphemes, sentence boundaries, syntactic structures, discourse structures, prosodic information, and the like. In
Japanese sentences, word order is flexible, and subjects orobjects are often omitted. In Japanese, therefore, the syntactic structure of a sentence is generally represented by the
relationship between phrasal units, bunsetsus in Japanese,
based on a dependency grammar, as represented in the Kyoto University text corpus (Kurohashi and Nagao, 1997).
In the same way, the syntactic structure of a sentence in
the CSJ is represented by the dependency relationships between bunsetsus (Uchimoto et al., 2006). However, in manycases, the syntactic structure of a bunsetsu is not consideredin syntactic structure annotation.
This paper mainly gives the dependency structure withinclauses and between bunsetsus in the CSJ and discusses relevant applications.

2. Dependency Structure in the CSJ
In general, a sentence is a necessary standard unit for natural language processing, syntactic analysis in linguistics,
and ordinary human-language activities. In dealing withspontaneous speech, however, a sentence is not necessarily appropriate for processing or analyzing because spontaneous speech basically contains no periods to mark sentence boundaries. Moreover, it is fundamentally difficult
to find obvious sentence boundaries in spontaneous utterances, which usually contain utterance errors, utterance
stops, and other characteristic phenomena. It is thus necessary to define and detect reasonable segmented units forprocessing as a “sentence” in spontaneous speech. In the

CSJ, therefore, “sentences” are defined as “clause units”.
These “clause units” were originally defined as the basic
processing units of spontaneous Japanese speech. They
can be obtained by automatically detecting Japanese clauseboundaries using the CBAP program (Maruyama et al.,2004) and then manually modifying them (Takanashi etal., 2003). Dependency relationships between bunsetsus
are annotated within “sentences” in the CSJ, and dependency relationships between words are annotated withinbunsetsus. Two types of word segments are defined in the
CSJ: short words and long words. The term short word
approximates an item found in an ordinary Japanese dictionary, and long word represents various compounds. In
this project, the word segments in a word-level dependency
structure are short words.
The criteria and definitions of dependency relationships between bunsetsus in the CSJ basically follow those in the Kyoto University text corpus. However, we added new criteria and definitions for dependency-structure annotation because there are many differences between written text andspontaneous speech, and the criteria and definitions in the
Kyoto University text corpus do not cover all the linguistic
phenomena observed in the CSJ.
In producing spontaneous speech, speech plans constructed
beforehand are sometimes changed during the utterance because of phonological, lexical, syntactic or ordering problems. In particular, long spontaneous monologues impose
heavy linearization problems on speakers, such as deciding
what to say first or next (Levelt, 1989). This causes various disfluencies, such as utterance stops, self-corrections,insertions, inversions, and distortions. For these disfluencies characteristic to spontaneous speech, dependency relationships between bunsetsus and between short words in abunsetsu are annotated in the following way.

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• Utterance stop
Utterance stops are basically detected as individual“sentences” in the CSJ, except if there is a depen-dency relationship between bunsetsus across an utterance stop. In that case, the utterance stop is defined tohave no modifiee.

short words and assigned with the label D in the sameway.

ex) “卵 (egg)” is an utterance stop and has no modifiee. In this example, each line represents a bunsetsu.

ex) “日 本 語 (Japanese)” is corrected to “ 国 語(Japanese language)” by the speaker. In this example,
each line represents a short word.

この─┐
家はですね─────────┐
卵│祖父が───────┤
はりきって───┤
一人で───┤建てましたの

国立───────────┐
日本─┐
│
語─Ｄ┐
│
国語─┐ │
研究─┤所─┐で(this)(house)(egg)(grandfather)(eagerly)(by himself)(built)• Inserted clause

The speaker wanted to say “This house, my grandfather eagerly built it by himself.” However, the word“egg” was inserted into the utterance to form “Thishouse is an egg, my grandfather eagerly built it byhimself.”

In spontaneous speech, speakers insert clauses in the
middle of other clauses. This occurs when they change
their speech plans while producing utterances, which
results in supplements, annotations, or paraphrases ofmain clauses. In the CSJ, inserted clauses are manually detected and bracketed with (. . .). Dependency
relationships within an inserted clause are closed, andthe boundaries of the inserted clause are detected
while detecting sentence boundaries.

An utterance stop is often preceded and followed bya short or longer pose. Therefore, an utterance stop
holding its meaning usually consists of one or morebunsetsus and is rarely found in a bunsetsu. When it isfound, it is a word fragment and already marked withthe label (D) in the CSJ. In this case, the utterance stopis also defined to have no modifiee.

An inserted clause consists of one or more bunsetsus
and is not found in a bunsetsu.
• Inversionex) “ろ” marked with (D) is an utterance stop and has
no modifiee. In this example, each line represents a
short word.
活用─────┐
(D ろ)
│
語尾─┐
と─┐
に

In the CSJ, inversions are represented as dependency
relationships going from right to left. Inversions are
not found in a bunsetsu.

(inflection)• Distortion(the ending of a word)case marker
case marker

Distortions are basically defined to have no modifiee
because the change of the speech plans causes a distortion, and the distorted sentence has an unnaturalsyntactic structure. Distorted sentences that include
topicalized expressions are often divided into different
sentences. Distortions are not found in a bunsetsu.

• Self-correction
In the CSJ, self-corrections are represented as dependency relationships between bunsetsus and assignedwith the label D. New criteria were established for annotating the self-corrections. Although there are various types of self-corrections, all of them were labeled
D because we focus not on classifying them into finegrained types but on discriminating them from ordinary dependency relationships.
ex) “山田 (Yamada)” is corrected to “ 山田さん (Mr.
Yamada)” by the speaker. In this example, each line
represents a bunsetsu.
山田─Ｄ┐
山田さんは────────┐
強靭な┐
│
肉体の─┐
│
持ち主だと──┤
言ってましたね(national)(Japanese)(word)(Japanese language)(research)(institute)case marker(Yamada)(Mr. Yamada)(strong)(body)(possessor)(said)

Self-corrections differ from dependency relationships aswell as from coordination and appositives. However, they
are represented as dependency relationships between bunsetsus, and the labels D, P, and A are assigned to selfcorrections, coordination, and appositives, respectively.
The definitions of coordination and appositives follow
those of the Kyoto University text corpus (Kurohashi andNagao, 1997). The definition of self-corrections and thoseof coordination and appositives for the word-level dependency structure were newly added to them 1 .

3.

Dependency-structure Annotation

Dependency relationships between bunsetsus were manually annotated to 199 speeches, which included all standard “core” monologues, and a test set in the CSJ. Dependency relationships between short words in a bunsetsu wereThis can be translated as “Yamada, Mr. Yamada said
that he had a strong body.”
When self-corrections are found in a bunsetsu, they
are represented as dependency relationships between

1
The detailed criteria for annotations to dependency relationships between bunsetsus is down-loadable from the CSJ web page
(CSJ, 2004). The detailed criteria for word-level dependencystructure annotation will also be available soon.

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Figure 1: Dependency-structure annotation tool.

also manually annotated to 50 speeches, which included themain parts of the standard monologues. The definition of abunsetsu followed that defined by the National Institute forJapanese Language (Nishikawa et al., 2004). The annotation tools shown in Figures 1 and 2 were used to assist human annotators. Each line represents a bunsetsu in Figure 1
and a short word in Figure 2, and each dependency can be
modified by a mouse drag-and-drop. Self-corrections, coordination, and appositives can be annotated with the labels
D, P, and A by right-clicking the mouse. Initial dependencies were annotated so that every bunsetsu and every shortword depends on the bunsetsu or short word. In the firstannotation step, two annotators examined each dependency
and modified it if it was inappropriate. In the second step,a checker examined all the dependencies annotated in thefirst step. The annotators referred to audio recordings aswell as transcriptions during these steps.

4.

Word-level Dependency-structure
Analysis

We investigated the word-level dependency accuracy in abunsetsu. Analyzing word-level dependency can be reduced to the problem of finding a modifiee for each word
in a bunsetsu. In Japanese, the rightmost word in a bunsetsu is the head of the bunsetsu and, in our experiments,
was assumed to have no modifiee. The input for a dependency analysis is the sequence of words in a bunsetsu
and their POS tags. Each word’s modifiee is determinedby using a dependency model. Therefore, the output is theset of dependencies between each word and its modifiee.
Existing methods, such as shift-reduce (Nivre and Scholz,
2004), were applied for the analysis 2 . In the shift-reduce
method, for example, four classes (left, right, shift, and reduce) should be discriminated for each pair of a target word
and its modifiee candidate. Therefore, an SVM multi-classclassifier based on pairwise coupling was used to discriminate the four classes. Two words on the left of the target
word and two words on the right of the modifiee candidate and the modifiers of the target word and those of themodifiee candidate were features. The distance between
the target word and its modifiee candidate was also used
as a feature. The 50 speeches annotated with word-level
dependency-structures were used for training and testing
the model. The dependency accuracies were calculated byusing 10-fold cross validation. Utterance stops were eliminated before the training and testing. The rightmost word ina bunsetsu is the root. The second rightmost word in a bunsetsu always depends on the next word. Therefore, every
rightmost dependency in a bunsetsu was not counted in theevaluation. The total number of dependencies was 33,429.
The dependency accuracies are shown in Table 1. The base2

For the MSTParser (http://sourceforge.net/projects/mstparser)
and CaboCha (http://chasen.org/˜taku/software/cabocha/), default
parameter settings were used. The default unit for CaboCha is abunsetsu. Therefore, each word was assumed to be a bunsetsu
when CaboCha was applied for the analysis.

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Figure 2: Word-level dependency-structure annotation tool.

line in the table is the accuracy obtained when we assumed
that every bunsetsu depended on the next one. There isno significant difference between the baseline accuracy andthe accuracy obtained by the existing methods. Improving
dependency accuracy is our future work. For this, semantic
relationships between words should be considered.
MethodBaseline
Shift-reduce (Nivre and Scholz, 2004)
MSTParser (McDonald et al., 2005)
CaboCha (Kudo and Matsumoto, 2000)

Dependency
accuracy
98.6%
99.1%
99.1%
99.1%

Table 1: Word-level dependency accuracy.

5. Towards Construction of Middle Words
Based on Word-level
Dependency-structure
In text-to-speech synthesis, pronunciation and accent information are required to naturally read out a given text written in Japanese kana and kanji. To indicate the appropriate pronunciation and accent, we need a basic unit wherea sound may change at the beginning or the ending of aword and/or an accent may change. For example, sequential voicing occurs by putting “ 段々(dandan)” (layered) and“畑 (hatake)” (fields) together to form a compound. Here,the ha of hatake is voiced as ba, and the compound wordis pronounced as dandanbatake (layered fields). This phenomenon is called “rendaku” (Weijer et al., 2005). As foraccent, the middle-accented word “dandanbaˆtake” (layered fields) is formed by putting the initial-accented word“daˆndan” and the unaccented word “hatake” together. On
the other hand, sequential voicing does not occur in “ 仮名(kana)” (kana) when “ 外来語 (gairaigo)” (foreign word)and “仮名表記 (kanahyouki)” (kana orthography) are put
together to form a compound, although it occurs when “
万葉 (manyo)”(myriad) and “ 仮名 (kana)” (kana) are put
together; the ka of kana is voiced as ga, and the compound word is pronounced as manyogana (manyogana).
In the above examples, “ 段々畑 (dandanbatake)”, “ 外来語 (gairaigo)”, “ 仮名表記 (kanahyouki)”, and “ 万葉仮名
(manyogana)” are suitable units to indicate the appropriate
pronunciation and accent. However, they are different fromthe existing two types of word segments, short words andlong words. The above examples are segmented as “ 段々(dandan)”, “ 畑 (hatake)”, “ 外来 (gairai)”, “語 (go)”, “仮名 (kana)”, “ 表記 (hyouki)”, “ 万葉 (manyo)”, and “ 仮名(kana)” for short words, and as “ 段々畑 (dandanbatake)”,“外来語仮名表記 (gairaigokanahyouki)”, and “ 万葉仮名
(manyogana)” for long words. Therefore, we propose constructing new basic units, middle words, that are defined asunits between short and long words and that will be usefulas constituents of accent phrases.
When putting words together to form a compound, a sound3121

change at the beginning or the ending of a word or an
accent change are blocked by right branched tree structures (Kubozono, 1995). For example, “ 外来語仮名表記(gairaigokanahyouki)” has a [[ 外来語 (gairaigo)] [ 仮名表記 (kanahyouki)]] structure where [ 仮名表記 (kanahyouki)]
is a right branch. Therefore, we define middle words asunits constructed by combining adjacent short words thathave dependency relationships within a long word.
Middle words are constructed on the basis of the following
rule.
• Combining adjacent short words that have dependency
relationships under the condition that a middle word is
not longer than a long word.
Morphological information is acquired in the followingway.
• If a middle word corresponds to a long word, morphological information of the middle word is extracted
from the long word.
• If the middle word does not correspond to a long word,morphological information of the middle word is extracted from the rightmost short word in the middle
word.
After eliminating utterance stops and self-corrections, we
automatically constructed middle words for 50 speeches in
the CSJ based on the word-level dependency structure mentioned in Section 2. We found the following relationships
between middle words and accent phrases (BI=2, 2+p, 2+b,
2+bp, 3) in the CSJ.
• The total numbers of short, middle, and long words
were 117,145, 97,644, and 97,167, respectively.
• The number of middle words that were constituentsof accent phrases in the CSJ was 94,702. Therefore,
2,942 middle words crossed the accent phrase boundaries in the CSJ.
• The number of long words that were constituents ofaccent phrases in the CSJ was 94,038. Of these, middle words corresponded to 93,797. It is desirable thatthe remaining 241 long words correspond to middle
words.
We plan to revise the rules for constructing middle words
so that the number of middle words that cross the accentphrase boundaries decreases and as many middle words as
possible correspond to long words.

6. Conclusion
In this paper we described the dependency structure ofa large spontaneous Japanese-speech corpus, Corpus of
Spontaneous Japanese (CSJ), and discussed the applicationof a word-level dependency-structure. We proposed constructing new basic units, middle words, that are defined asunits between short and long words and that will be usefulas constituents of accent phrases. The word-level dependency structure and middle words annotated to the CSJ will
be available to the public. We plan to use the data to annotate word-level dependency structures and middle words

to the Balanced Corpus of Contemporary Written Japanese(BCCWJ), the compilation and analysis of which is supported by the priority area program ‘Japanese Corpus’, afive-year (2006-2010) project.

7.

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