Help:Extension:Translate/Translation memories

TTMServer is a translation memory that comes with the Translate extension. It needs no external dependencies. It is enabled by default and it replaces the support for tmserver from translatetoolkit, which was hard to set up. TTMServer is a simple translation memory and doesn't use any advanced algorithms. It takes advantage of MediaWiki's excellent language support and database abstraction features.

There are three different ways to use TTMServer:

All suggestion services including translation memories are configured with the  configuration setting. Example configuration of TTMServers:

Possible keys and values are:

Currently only MySQL is supported for the databases.

TTMServer API
Would you like to implement your own TTMServer service, here are the specifications.

Query parameters: Your service must accept the following parameters:

Your service must provide JSON object which must have key  with array of objects. Those objects must contain the following data:

Example:
 * URL: http://translatewiki.net/w/api.php?action=ttmserver&sourcelanguage=en&targetlanguage=fi&text=january&format=jsonfm
 * Response:

TTMServer architecture
The backend contains three tables,,   and. Those correspond to sources, targets and fulltext. You can find the table definitions in. The sources contain all the message definitions. Even though usually they are always in the same language, say, English, the language of the text is also stored for the rare cases this is not true.

Each entry has a unique id and two extra fields, length and context. Length is used as the first pass filter, so that when querying we don't need to compare the text we're searching with every entry in the database. The context stores the title of the page where the text comes from, for example "MediaWiki:Jan/en". From this information we can link the suggestions back to "MediaWiki:Jan/de", which makes it possible for translators to quickly fix things, or just to determine where that kind of translation was used.

The second pass of filtering comes from the fulltext search. The definitions are mingled with an ad-hoc algorithm. First the text is segmented into segments (words) with MediaWiki's. If there are enough segments, we strip basically everything that is not word letters and normalize the case. Then we take ten first unique words, which are at least 5 bytes long (5 letters in English, but even shorter words for languages with multibyte code points). Those words are then stored in the fulltext index for further filtering for longer strings.

When we have filtered the list of candidates, we fetch the matching targets from the targets table. Then we apply the levenshtein edit distance algorithm to do the final filtering and ranking. Let's define:
 * E :edit distance
 * S :the text we are searching suggestions for
 * Tc :the suggestion text
 * To :the original text which the Tc is translation of

The quality of suggestion Tc is calculated as E/min(length(Tc),length(To)). Depending on the length of the strings, we use: either PHP's native levenshtein function; or, if either of the strings is longer than 255 bytes, the PHP implementation of levenshtein algorithm. It has not been tested whether the native implementation of levenshtein handles multibyte characters correctly. This might be another weak point when source language is not English (the other being the fulltext search and segmentation).

There is a script which fills the translation memory with translations from the active message groups. Even big sites should be able to bootstrap the memory in half an hour when using multiple threads with the  parameter. The time depends heavily on how complete the message group completion stats are (incomplete ones will be calculated during the bootstrap). New translation are automatically added by a hook. New sources (definitions) are added when first translation is added. Old translations which are no longer used and do not belong to any message groups are not purged automatically, unless you rerun the bootstrap script. When the translation of a message is updated, the previous translation is removed from the memory. When the definition is updated nothing happens immediately. When translations are updated against the new definition, a new entry will be added. The old definition and its old translations remain in the database until purged by rerunning the bootstrap script. Also fuzzy translations will not be added to the translation memory, but neither are the translations removed from the memory when they are fuzzied.