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From "Tansley, Robert" <>
Subject Indexing multiple languages
Date Tue, 31 May 2005 21:08:39 GMT
Hi all,

The DSpace ( currently uses Lucene to index metadata
(Dublin Core standard) and extracted full-text content of documents
stored in it.  Now the system is being used globally, it needs to
support multi-language indexing.

I've looked through the mailing list archives etc. and it seems it's
easy to plug in analyzers for different languages.

What if we're trying to index multiple languages in the same site?  Is
it best to have:

1/ one index for all languages
2/ one index for all languages, with an extra language field so searches
can be constrained to a particular language
3/ separate indices for each language?

I don't fully understand the consequences in terms of performance for
1/, but I can see that false hits could turn up where one word appears
in different languages (stemming could increase the changes of this).
Also some languages' analyzers are quite dramatically different (e.g.
the Chinese one which just treats every character as a separate

On the other hand, if people are searching for proper nouns in metadata
(e.g. "DSpace") it may be advantageous to search all languages at once.

I'm also not sure of the storage and performance consequences of 2/.

Approach 3/ seems like it might be the most complex from an
implementation/code point of view.  

Does anyone have any thoughts or recommendations on this?

Many thanks,

 Robert Tansley / Digital Media Systems Programme / HP Labs

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