Supported character sets

mnoGoSearch supports almost all known 8 bit character sets (later called charsets) as well as some multi-byte charsets including Korean EUC-Kr, Chinese big5 and GB2312, Japanese shift-JIS, EUC-JP and ISO-2022-JP, as well as UTF8. Some multi-byte charsets are not supported by default, because the conversion tables for them are rather large and that leads to a considerable increase of the executable files size. See configure parameters to enable support for these charsets.

mnoGoSearch also supports the following Macintosh character sets: MacCE, MacCroatian, MacGreek, MacRoman, MacTurkish, MacIceland, MacRomania, MacThai, MacArabic, MacHebrew, MacCyrillic, MacGujarati.

Several languages in one database

It is often necessary to deal with several languages simultaneously. The number of supported languages depends on the choice of charset that mnoGoSearch will use to store data. The charset is specified by the LocalCharset command.

UTF-8 mode

When UTF-8 is specified in the LocalCharset command, you may work with any languages supported in Unicode. That means you may use any number of over 650 languages. However, using UTF-8 may consume a large amount of disk space (up to twice for some languages), leading to slower indexation and search.

non-UTF-8 mode

Since every character set includes Latin characters, any character set supports at least two languages - English and one or more other languages. US-ASCII is an exception - it supports only Latin characters.

E.g. in case your search engine was configured to use LocalCharset from the 5th group (Cyrillic), you may index servers containing documents in Bulgarian, Belorussian, Macedonian, Russian, Serbian and Ukrainian. Indexing a multi-language document in UTF-8 is possible as well; however, the indexer will extract and save only Cyrillic content from the page. To provide support for over 650 languages, please use LocalCharset UTF-8.

Recoding

The indexer recodes all documents to the character set specified in the indexer.conf LocalCharset command. Internal recoding is implemented using Unicode. Please note that some recoding procedures may loose some data. For example, recoding between any Greek and Russian charsets looses all national characters. This does not matter for a single language sites. If you want to build multi-lingual search engine use the UTF8 character set as LocalCharset.

Recoding at search time

You may use the BrowserCharset command to choose a charset which will be used to display search results. BrowserCharset may differ from LocalCharset.

Character sets aliases

Each charset is recognized by a number of its aliases. Different web servers could return the same charset in different notations. For example, ISO-8859-2, ISO8859-2, latin2 are the same charsets. The search engine understands the following charsets names aliases:

Document charset detection

The indexer detects document charsets in this order:

1. "Content-type: text/html; charset=xxx"

2. <META NAME="Content-Type" CONTENT="text/html; charset=xxx"> (for HTML documents) or

   <?xml version="1.0" encoding="xxx"?> (for XML documents)

   The selection of this variant may be switched off by using the: GuesserUseMeta no command in your indexer.conf.

3. The defaults to "Charset" settings of the corresponding Server or Realm command.

Automatic charset guesser

Since 3.2.0, mnoGoSearch has an automatic charset and language guesser. It currently recognizes more than 100 various charsets and languages. Charset and language detection is implemented using the "N-Gram-Based Text Categorization" technique. There is a number of so called "language map" files, one for each language-charset pair. They are installed under /usr/local/mnogosearch/etc/langmap/ directory by default. Take a look there to check the list of currently provided charset-language pairs. Guesser works fine for texts bigger than 500 characters. Shorter texts may not be guessed well.

        mguesser -p -c charset -l language < FILENAME > language.charset.lm

        mguesser [-n maxhits] < FILENAME

        mconv [OPTIONS] -f charset_from -t charset_to [configfile] < infile > outfile

Since version 3.2.14, mnoGoSearch has an ability to update language and charset maps automatically while indexing, if the remote server supplies pages with exactly specified language and charset. To enable this function, specify command

LangMapUpdate yes

Default charset

Use the RemoteCharset indexer.conf command to choose the default charset of indexed servers.

Default Language

You can set the default language for Servers by using the DefaultLang indexer.conf command. This is useful for further restricting search results language.