Sentence-Style Conversion of Japanese News Article
for Text-to-Speech Application
Yukiko Hayashi1

Shigeki Matsubara2

1 Graduate School of Information Science, Nagoya University, Japan
2 Information Technology Center, Nagoya University, Japan
1 hayashi@el.itc.nagoya-u.ac.jp

Abstract
This paper proposes a method ofsentence-style conversion for generating spontaneous Japanese speech
in a text-to-speech synthesis system.
Since written language is diﬀerent
from spoken language linguistically,
the speech by direct reading of written Japanese texts might be unnatural. The method takes a fully rulebased approach to convert the sentence style and to complement sentences, which are lacking some functional words or verbs. The method
was evaluated using Japanese newspaper articles. The precision was
89.7%, and the recall was 86.7%.

1

Introduction

There are huge quantities of printed media
such as newspapers, magazines, web sites, email. At the same time, we are not always able
to spend a great deal of time reading these vast
amounts of texts, and therefore the method foreﬃciently surveying these texts is desired. For
example, by listening speech generated fromthe texts while driving or walking, we can get
the information eﬃciently.
In order to generate speech from texts automatically, we can use text-to-speech systems.
Recent text-to-speech systems have been improved in quality of sound, and can produce
speeches with almost human-like pauses andintonation. Between written language and spoken language, however, there exist many diﬀerences in vocabulary, phrases, and so on. Thismeans that the speech directly generated fromwritten-style texts might be unnatural.
This paper proposes a method of sentencestyle conversion for generating spontaneous
Japanese speech in a text-to-speech synthesis
system. The articles in a newspaper are usedas the objects of the conversion, for the reason

2 matubara@itc.nagoya-u.ac.jp

that we are planning to deliver spoken news
generated from texts automatically.
Ohizumi et al. proposed a method of converting nominalized verbs as a part of their research on paraphrasing written language into
spoken language (Ohizumi et al., 2003). They
did not treat taigen-dome,1 a Japanese-speciﬁcrhetoric, however, which we discuss in thispaper. Kaji et al. proposed a method ofparaphrasing written-language-speciﬁc vocabulary into spoken-language-speciﬁc vocabularyby using written and spoken language corpora
collected from the Web (Kaji et al., 2004).
This study takes particular note of the importance of the diﬀerences between “da-dearu”
style (written style) and “desu-masu” style(spoken style), and also works on “taigendome.”Taigen-dome sentences need to be complemented with an appropriate word. We takea fully rule-based approach to convert the sentence style and to complement taigen-domesentences. The experiment was conducted onJapanese newspaper corpus, and the precision
was 89.7%, the recall was 86.7%.
This paper is organized as follows: Section 2
discusses the diﬀerences between written language and spoken language. Section 3 describes a method of sentence-style conversion.
Section 4 reports the experimental results.

2

Diﬀerences between Written
Language and Spoken Language

In general, natural language is divided into
written language and spoken language. Written language is used for text-based communications, and spoken language for speech-based
communications. Table 1 shows the diﬀerences
1
Taigen-dome is a rhetoric to cut oﬀ the words following a certain noun in order to end the sentence with
the noun. The eliminated words, however, have to beinferable from the context. In Japanese, taigen means
an indeclinable word including a noun and a pronoun,
and dome means “to end,” hence taigen-dome approximately corresponds to “ending-with-noun.” By doing
this, the writer can make an impression on the reader.

A newspaper article in written language
murayama-tomiichi-shusho-wa nento-no kisha-kaiken-de sozo-to yasashisa-no kuni-zukuri-no bijon-to daisuru
shokan-o happyo-shita.
kongetsu-chu-ni shusho-o kakomu gakusha-gurupu-ga happyo-suru murayama-bijon-no kihon-teki-na kangae-oshimeshi-ta mono.
waga-kuni-ni fusawashi kokusai-koken-niyoru sekai-hewa-no sozo-to meiut-ta hi-gunji-bunya-no kokusai-kokennado yottsu-no sozo-o uchidashi-te iru.
shokan-wa boto-de sengo goju-shunen-no fushime-no toshi-no kyatchi-furezu-o kaikaku-kara sozo-e-to hyogen.
A newspaper article converted into spoken language
murayama-tomiichi-shusho-wa nento-no kisha-kaiken-de sozo-to yasashisa-no kuni-zukuri-no bijon-to daisuru
shokan-o happyo-shi-mashi-ta.
kongetsu-chu-ni shusho-o kakomu gakusha-gurupu-ga happyo-suru murayama-bijon-no kihon-teki-na kangae-oshimeshi-ta mono-desu.
waga-kuni-ni fusawashi kokusai-koken-niyoru sekai-hewa-no sozo-to meiut-ta hi-gunji-bunya-no kokusai-kokennado yottsu-no sozo-o uchidashi-te i-masu.
shokan-wa boto-de sengo goju-shunen-no fushime-no toshi-no kyatchi-frezu-o kaikaku-kara sozo-e-to hyogenshi-te i-masu.
(Prime Minister Tomiichi Murayama oﬀered his view titled “The nation-building vision with creation and benevolence” at the ﬁrst-of-the-year press interview. This view demonstrates basic policies of “Murayama Vision” which
the prime minister’s brain trust will announce later this month. His view presents “the four creation” including
a international contribution in the nonmilitary sector named “The creation of global peace by a international
contribution suited to our country.” The view initially described the catch-phrase of this milestone year being the50th anniversary of the end of the Paciﬁc War as “From reform into creation.”)Figure 1: Comparison between written language and spoken language.
Table 1: Diﬀerences between written language
and spoken language.

Tone of the words

Written language
mainlydadearu stylerather longrather diﬃcult
rather formal

Diﬀusenesslow

Sentence style
Length of sentence
Vocabulary

Spoken language
mainly desumasu stylerather shortrather easyrather informalhighbetween written language and spoken language(Yamamoto et al., 2003; Ohizumi et al., 2003).
In this paper, among the diﬀerences between
written language and spoken language, we takeup a sentence style and diﬀuseness. Note that
we equate diﬀuseness with taigen-dome sentences. Figure 1 shows the comparison between written language and spoken language
using an actual newspaper article. The differences in sentence style and the taigen-domesentence are indicated by boldface.
2.1 Diﬀerences of Sentence Style
The diﬀerences of the sentence style distinguish spoken language from written language.
Desu-masu style is important for listeners inreceiving the speech naturally.
2.2 Taigen-dome sentences
Taigen-dome is a rhetoric to end the sentencewith the noun as noted in the footnote in Sec-tion 1. The following are examples:• yoshi-wa tsugi-no tori (desu).
(The summary is as follows.)• taisaku-no hitsuyosei-o shiteki(shi-mashi-ta).
(He indicated the need for countermeasures.)

Both of the example sentences end with anoun (“tori” and “shiteki”), and the words inparentheses (“desu” and “shi-mashi-ta”) are
the eliminated words which can be inferredfrom the context information.
Taigen-dome sentences occur frequently innewspaper articles. They are intended to eliminate the diﬀuseness and condense the articles
as well as to leave the readers with an impression. On the other hand, a taigen-dome sentence in speech is unnatural because such asentence sounds like it was cut oﬀ halfway. In
order to make it natural, we need to complement it with an appropriate word.

3

Conversion from Written
Language into Spoken Language

3.1 Conversion of Sentence Style
We adapt a rule-based approach in order toconvert written-style sentences into spokenstyle sentences. The rules are based on word
sequences and morphological information suchas surface string, part of speech, and conjugation. The rules were made by analyzing 1130
sentences in articles on January 1st, 1995 inTable 3: Experimental results.
the Mainichi newspaper text corpus. Table 2
shows the conversion rules and the respective
examples.
3.2

Complement of taigen-domesentences

In complementing taigen-dome sentences,
there exist three kinds of points to be taken
into account in.
(1) Type of the complementary word
As noted in Section 2.2, the complementary
word of the taigen-dome sentence varies depending on the context. In order to determine
the type of the complementary word, we focused on the subtype of the last noun of thesentence.
For example, in the sentence “yoshi-wa
tsugi-no tori.,” the subtype of the last noun
“tori” is “general.” In the sentence “taisaku-no
hitsuyosei-o shiteki.,” the subtype of the lastnoun “shiteki” is “sahen.” The subtype “sahen” means that the noun is a verbal noun andcan be followed by a verb “shi-masu” which isroughly the English equivalent of “do.”Thus, if the last noun of a sentence is a“sahen” noun, the sentence is complemented
by “shi-masu” or its past form “shi-mashita,” otherwise it is complemented by “desu”
or its past form “deshi-ta.” In the sentence“kankoku-gawa-kara gutai-teki-na tean-ga aru
yote. (South Korea will make a concrete suggestion.)”, however, although the last noun
“yote” is “sahen” noun, the proper complement of the sentence is “desu.” Thus, even if
the last noun is a “sahen” noun, a sentence including the word which can become the subject
is complemented by “desu” or its past form.
(2) Tense
In addition to the type of the complementary word, we have to decide the proper tenseof the word. In order to determine the tense,
we use the particular auxiliary verb and thephrase which indicates the past form. A sentence which includes any of the words listed
below is considered as the past tense.
• Auxiliary verb “ta” which indicates the pastform.
• The phrases which indicates the past form
such as “sakunen (last year),” “san-nen-mae(three years ago).”Precision
619/690 (89.7%)

Recall619/714 (86.7%)

F-measure88.2(3) Necessity of the complement
There exists a taigen-dome sentence whichneeds no complement. For example, a sentence “kanada-no ese-toshi-gun-no hitotsu ricchimondohiru. (Richmond Hill, one of Canadian satellite cities.)” needs no complement. If
it were complemented by a word like “desu,”
it would be considerably artiﬁcial. Therefore,
if the subtype of the last noun in a sentence is
not “sahen” and the sentence does not include
the word which can become a subject, the sentence is considered to need no complement.
In consideration of the above three viewpoints, we made the decision tree as shown in
Figure 2. The complementary word for eachtaigen-dome sentence is determined according
to this decision tree.

4

Experiment

The articles on January 3rd, 1995 in theMainichi newspaper text corpus were used as
an experimental object. The articles consist of
687 sentences including 714 places to be converted. Of them, 559 are written-style (dadearu style) and 155 are taigen-dome. The
rules in Table 2 were used to convert the sentence style. The decision tree in Figure 2
was used to complement the taigen-dome sentences. For morphological analysis, MeCab(Kudo, 2006) was used. Table 3 shows the precision and the recall of the whole experiment.
The precision and recall were as follows:# of correctly converted places# of converted places# of correctly converted places
Recall= # of places to be converted

P recision=

The experimental results of sentence-style
conversion and the results of taigen-domesentences complement are separately discussed
below.
4.1 Results of Sentence-style Conversion
Among the 687 sentences in the article on January 3rd, 1995 in the Mainichi newspaper text
corpus, there exist 559 places to be converted
from written style into spoken style. Table 4shows the results of sentence-style conversion.
The precision was rather high. The only error

Table 2: Conversion rules and examples.
Conversion rule
1. BF of a verb → CF of the verb + “masu”
2. CF of a verb + BF of an auxiliary verb“ta” → CF of the verb + “mashi-ta”
3. IF of a verb + BF of an auxiliary verb
“nai” → IF of the verb + “mase-n”
4. IF of a verb + CF of an auxiliary verb
“nai” + BF of an auxiliary verb “ta” →IF of the verb + “mase-n-deshi-ta”
5. BF of an auxiliary verb “da” → “desu”

6. CF of an auxiliary verb “da” + BF of an
auxiliary verb “ta” → “deshi-ta”
7. BF of an auxiliary verb “nai” → “arimase-n”
8. CF of an auxiliary verb “da” + BF of an
auxiliary verb “aru” → “desu”
9. CF of an auxiliary verb “da” + CF ofan auxiliary “aru” + BF of an auxiliary“ta” → “deshi-ta”
10. CF of an auxiliary verb “da” + IF of
an auxiliary “aru” + BF of an auxiliaryverb “u” → “desho-u”

Before conversion
After conversion
risuto-ni-wa samazama-na uttae-ga risuto-ni-wa samazama-na uttae-ga
narabu.
narabi-masu.
(Various appeals are on the list.)
sefu-suji-ga sanjuichi-nichi akiraka- sefu-suji-ga sanjuichi-nichi akirakani shi-ta.
ni shi-mashi-ta.
(Government sources showed it on 31st.)
judan-wa mitsukat-te i-nai.
judan-wa mitsukat-te i-mase-n.
(The bullet has yet to be found.)kyoi-ni omot-ta kankesha-wa ho- kyoi-ni omot-ta kankesha-wa hotondo i-nakat-ta.
tondo i-mase-n-deshi-ta.
(There were few participators who thought is as a threat.)se-to
kan-gaittai-ni
nat-te se-to
kan-gaittai-ni
nat-tekokumin-ni kotae-te ika-nakere-ba kokumin-ni kotae-te ika-nakere-ba
nara-nai kadai-da.
nara-nai kadai-desu.
(It is a problem which requires a joint eﬀort by statesman and bureaucrats.)
sore-wa
konphuta-hyogen-no sore-wa
konphuta-hyogen-nomannerizumu-o migoto-ni daha- mannerizumu-o migoto-ni dahasita mono-dat-ta.
sita mono-deshi-ta.
(It broke down the mannerism of computer art wonderfully.)
tonai-ni sorehodo-no doyo-wa nai.
tonai-ni sorehodo-no doyo-wa arimase-n.
(The party members are not so upset.)ta-no tsuiju-o yurusa-nai tokoro- ta-no tsuiju-o yurusa-nai tokorode-aru.
desu.
(There is nothing comparable to it.)dokuji-no sakufu-o uchitate-ta-no- dokuji-no sakufu-o uchitate-ta-node-at-ta.
deshi-ta.
(He established a original style.)jiyu-na sekai-ga kuru-to shinji-ta- jiyu-na sekai-ga kuru-to shinji-takara-de-aro-u.
kara-desho-u.

(This was likely because she believed that the free world would come.)
kesshite raku-na tatakai-de-wa-nai- kesshite raku-na tatakai-de-wa-naidaro-u.
decho-u.
(It will never be an easy ﬁght.)
12. a conjunction “daga” or “ga” → daga jisshitsu-shotoku-wa gekigen- desu-ga
jisshitsu-shotoku-wa“desuga”
shi-te iru.
gekigen-shi-te i-masu.
(But actual real income has fallen dramatically.)
13. BF of an adjective “nai” → “ari-mase-n” kori-to wakat-te i-te-mo hoka-ni kori-to wakat-te i-te-mo hoka-ni
sentakushi-ga nai.
sentakushi-ga ari-mase-n.
(They have no choice but to borrow the money from loan sharks.)
14. CF of an adjective “nai” + BF of an aux- kozoku-no unko-ni sisho-wa nakat- kozoku-no unko-ni sisho-wa ariiliary verb “ta” → “ari-mase-n-deshi-ta” ta.
mase-n-deshi-ta.
(It did not interrupt the following service.)
BF: basic form, CF: conjunctive form, IF: imperfective form
11. IF of an auxiliary verb “da” + BF of an
auxiliary “u” → “desho-u”

Table 4: Results of sentence-style conversion.
Precision
525/526 (99.8%)

Recall525/559 (93.9%)

F measure
96.8

was as follows. ((a) is a original sentence, (b)is the converted sentence.)
1. (a) kantoku-no hyojo-wa ima-hitotsu saenakat-ta.
(b) kantoku-no hyojo-wa ima-hitotsu sae
ari-mase-n-deshi-ta.
(The coach’s expression was not quite
good.)In this sentence, the predict “sae-nakat-ta”
should be converted into “sae-mase-n-deshita” based on the rule 4 in Table 2. In theexperiment, however, “sae” was regarded as an

Table 5: Causes of the failed conversion.
Causesentences ending with an adjective
othersNumber22
12intensifying particle (which means “even”) by
the morphological analyzer, despite “sae” is actually a stem of a verb “sae-ru” (which means“to feel good”). Therefore, this sentence wasconverted according to the rule 14 instead of
the rule 4 shown in Table 2.
The recall was slightly lower than the precision. Table 5 shows the causes of failure toconvert 34 places. The details are below.
Sentences ending with an adjective
If a sentence ends with an adjective, it is difﬁcult to create rules for converting the sentenceDoes the sentence
include the word thatcan become thesubject ?
sahenDoes the sentence
include the word that
implies the pasttense ?
Yes

past form[deshi-ta]

Yes

present form

[desu]

No

past form[shi-mashi-ta]

Yes

No

What is the subtypeof the last nounin the sentence ?

present formNo[shi-masu]
past form[deshi-ta]

Yes
the others

Yes

present formNo

[No complement
necessary]No

Deciding the kind of
the complementary word

[desu]

Deciding the tense of
the complementary word

Figure 2: Decision tree for determining the complementary word of taigen-dome sentence.
because it requires contextual information toconvert this kind of sentences properly. The
following are sentences which were unable tobe converted into spoken style and their proper
conversion. ((a) is a original sentence, (b) is
the properly converted sentence.)
2. (a) honkon-ni yat-te-kuru chugokujin-ya
gaikokujin-mo oi.
(b) honkon-ni yat-te-kuru chugokujin-ya
gaikokujin-mo oku-i-masu.
(There are a great deal of Chinese andpeople from other countries who come toHong Kong.)
3. (a) mushiro kange-sa-re-te iru-to it-te-moyoi.
(b) mushiro kange-sa-re-te iru-to it-te-mo
yoi-desho.
(It’s not an exaggeration that they are
more welcomed.)

The last adjectives “oi” and “yoi” can beconverted into “oi-desu” and “yoi-desu” respectively. The converted adjectives are grammatically correct, but unnatural in speech.
The others
The sentences ending with a word “shitai”(would like to) or “rashi”(to seem), as withthe sentences ending with an adjective, canbe converted into “shitai-desu,” “rashi-desu”
respectively, however, they are unnatural in

Table 6: Results of taigen-dome-sentence complement.
Precision
94/164 (57.3%)

Recall
94/155 (60.6%)

F-measure
58.9

Table 7: Causes of the faulty complement.
Cause
tense
type of the complementary word
necessity of the complement

Number47
19
4

speech. It is diﬃcult to create rules for converting these sentences and it is necessary toconsider a method of context-sensitive conversion.
Results of Taigen-dome-Sentence
Complement
In the articles on January 3rd, 1995 in theMainichi newspaper text corpus, 155 of 687
sentences need to be complemented. Table 6
shows the experimental results of the taigendome-sentence complement. Table 7 showscauses of the faulty complements. The detailsof the causes are below. In the following examples, (a) is the sentence complemented incorrectly by our method, (b) is the correctly
complemented sentence.
4.2

Tense
4. (a) sakunen sangatsu-no sutato-irai kanyusha-wa nenmatsu-made-ni yaku-nimannin-deshi-ta.

(b) sakunen sangatsu-no sutato-irai kanyusha-wa nenmatsu-made-ni yaku-nimannin-desu.
(Since the start in last March, the number of subscribers has increased to about
20 thousand by the end of this year.)In this example, the sentence includes the word
“sakunen (last year)” which implies the pasttense. Actually, however, the present tense issuitable for this sentence considering the context information.
The presence of the auxiliary verb “ta” or
the word which implies the past tense is not
suﬃcient to determine the tense of the sentence.
Type of the complementary word
5. (a) kaigai-no gakko-ya byoin-ni taisuru
shakai-koken-katsudo-ni-mo
sefu-nokise-no ami-desu.
(b) kaigai-no gakko-ya byoin-ni taisuru
shakai-koken-katsudo-ni-mo
sefu-nokise-no ami-ga kakari-masu.
(The governmental regulations are imposed on social action programs for foreign schools or hospitals.)This indicates that the more kinds of thecomplementary words are required in addition
to “desu,” “deshi-ta,” “shi-masu,” “shi-mashita.” Another examples are as follows:• nihon-sanke-no miyajima-wa futsuka-kan-de
kyuman-nin. (ga otozure-mashi-ta)(Miyajima, one of the three most scenic spots
in Japan, was visited by 90 thousand people
in two days.)• kokoku-wa kaku-peji-no gedan-ni-kesai. (saremasu)(The advertisement is put on the bottom ofeach page.)

Necessity of the complement
6. (a) bekoku-no gasu-gaisha-de kono-ni-sannen-no aida-ni shiken-teki-ni jisshi-sarete iru shikumi (no word was complemented).
(b) bekoku-no gasu-gaisha-de kono-ni-sannen-no aida-ni shiken-teki-ni jisshi-sarete iru shikumi-desu.
(It is a scheme which American gas companies have introduced on a trial basis inthese years.)

In this example, the sentence does not include the word which can become subject.

Therefore, according to the decision tree in
Figure 2, the sentence was not complemented
even though it needs to be complemented by“desu.” We need to review the complement
rules which determine the sentence needs tobe complemented.

5Concluding Remarks

In this paper, we have proposed a method of
conversion from written language into spoken
language for generating spontaneous Japanese
speech in a text-to-speech synthesis system.
We focused on sentence-style conversion andcomplement of taigen-dome sentences. For
sentence-style conversion, we took a fully
rule-based approach, and conﬁrmed that only
the lexical analysis could achieve the highprecision conversion by the experiment. In theexperiment of the complement of taigen-domesentences, the precision and the recall were nothigh.
In future work, the complement rule fortaigen-dome sentences will be reconsidered.
We have a plan to introduce a machine learning approach to generate the complement ruleautomatically using a large-scale spoken language corpus.

References
Masako Yamamoto, Goroh Ohnishi.
2003.
Hanashi-kotoba to Kaki-kotoba no Sogo-kanke— Nihongo Kyoiku no Tameni —. Language
and Culture (Bulletin of Institute for Language
Education, Aichi University), No. 8, pp. 73-90.
(in Japanese)
Toshiki Ohizumi, Nobuhiro Kaji, Daisuke Kawahara, Masashi Okamoto, Sadao Kurohashi, andToyoaki Nishida.
2003.
Kaki-kotoba kara
Hanashi-kotoba eno Henkan. In Proceedings of
The 9th Annual Meeting of The Association for
Natural Language Processing (NLP-2003), pp.
93-96. (in Japanese)
Nobuhiro Kaji, Masashi Okamoto, and Sadao
Kurohashi. 2004. Paraphrasing Predicates fromWritten Language to Spoken Language Using
the Web. In Proceedings of the Human Language Technology Conference (HLT/NAACL2004), pp. 241-248.
Taku Kudo. MeCab: Yet Another Part-of-Speechand Morphological Analyzer.
http://mecab.sourceforge.jp/.