science

MeCab

MeCab is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand MeCab rather than just read about it. In short: MeCab is an open-source text segmentation library for Japanese written text. It was originally developed by the Nara Institute of Science and Technology and is maintained by Taku Kudo (工藤拓) as part of his work on the Google Japanese Input project.

Key takeaways

MeCab belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MeCab to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MeCab from memory before moving on to harder problems.

Reference excerpt

MeCab is an open-source text segmentation library for Japanese written text. It was originally developed by the Nara Institute of Science and Technology and is maintained by Taku Kudo (工藤拓) as part of his work on the Google Japanese Input project. The name derives from the developer's favorite food, mekabu (和布蕪), a Japanese dish made from wakame leaves. The software was originally based on ChaSen and was developed under the name ChaSenTNG, but now it is developed independently from ChaSen and was rewritten from scratch. MeCab's analysis accuracy is comparable to ChaSen, and it is about 3–4 times faster. MeCab analyzes and segments a sentence into its parts of speech. There are several dictionaries available for MeCab, but IPADIC is the most commonly used one as with ChaSen. In 2007, Google used MeCab to generate n-gram data for a large corpus of Japanese text, which it published on its Google Japan blog. MeCab is also used for Japanese input on Mac OS X 10.5 and 10.6, and in iOS since version 2.1.

Example Input:

ウィキペディア（Ｗｉｋｉｐｅｄｉａ）は誰でも編集できるフリー百科事典です Results in:

ウィキペディア名詞,一般,*,*,*,*,* （記号,括弧開,*,*,*,*,（,（,（Ｗｉｋｉｐｅｄｉａ名詞,固有名詞,組織,*,*,*,* ）記号,括弧閉,*,*,*,*,）,）,）は助詞,係助詞,*,*,*,*,は,ハ,ワ誰名詞,代名詞,一般,*,*,*,誰,ダレ,ダレでも助詞,副助詞,*,*,*,*,でも,デモ,デモ編集名詞,サ変接続,*,*,*,*,編集,ヘンシュウ,ヘンシューできる動詞,自立,*,*,一段,基本形,できる,デキル,デキルフリー名詞,一般,*,*,*,*,フリー,フリー,フリー百科名詞,一般,*,*,*,*,百科,ヒャッカ,ヒャッカ事典名詞,一般,*,*,*,*,事典,ジテン,ジテンです助動詞,*,*,*,特殊・デス,基本形,です,デス,デス EOS

Besides segmenting the text, MeCab also lists the part of speech of the word, and, if applicable and in the dictionary, its pronunciation. In the above example, the verb できる (dekiru, "to be able to") is classified as an ichidan (一段) verb (動詞) in the infinitive tense (基本形). The word でも (demo) is identified as an adverbial particle (副助詞). As not all columns apply to all words, when a column does not apply to a word, an asterisk is used; this makes it possible to format the information after the word and the tab character as the comma-separated values. MeCab also supports several output formats; one of which, chasen, outputs tab-separated values in a format that programs written for ChaSen can use. Another format, yomi (from 読む yomu, to read), outputs the pronunciation of the input text as katakana, as shown below.

ウィキペディア（Ｗｉｋｉｐｅｄｉａ）ハダレデモヘンシュウデキルフリーヒャッカジテンデス

References

External links Official website

Worked examples

Example 1 — a first encounter with MeCab

Start with the simplest possible case. Write down what MeCab claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to MeCab before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about MeCab ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of MeCab

In research: MeCab appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses MeCab in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: MeCab is common in secondary-school and first-year university syllabi. It links to neighbouring topics Natural language processing, so understanding it makes those chapters shorter.
In everyday life: Look for MeCab outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “MeCab” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study MeCab in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MeCab means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain MeCab out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MeCab in simple terms?

Why does MeCab matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study MeCab?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on MeCab.