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From Ted Dunning <>
Subject Re: index per-user basis and document frequency
Date Mon, 15 Jun 2009 22:16:00 GMT
I don't think that this would be such a great idea.

Better to use a custom
structure.  Before you do that, though, you might try just using the
overall corpus statistics and not worry about this per user indexing with
specialized statistics.  If users' are no more different from each other
than sub-corpora in a normal retrieval system then you are liable to get
much better results using corpus wide stats than with user level stats.

On Mon, Jun 15, 2009 at 2:06 PM, Lionel Duboeuf

> Hi,
> I use Lucene to index user's documents. I have a potential of 2 or more
> millions users so that i think a per-user index will not be a scalable
> solution. All my searches are filtered with a user UID  field.
> As far as i know the default similarity calculate Inverse Document
> Frequency  as follow:
> Math.log(numDocs/(double)(docFreq+1)) + 1.0)
> where numDocs stands for the number of documents within the whole
> collection and docFreq for the number of times Term t appear in the whole
> collection.
> My problem here is that this formula seems not to be reliable for my system
> because numDocs should correspond to the number of documents in the user's
> collection  and docFreq for the number of times the Term T appears in the
> user's collection.
> Because Terms are stored as a single token i was thinking of concatenating
> terms with a UID in order to separate them because :
> Term "car" for user1 is different to term "car" for user2. My solution
> would index "carUSERUID1" "carUSERUID2".
> What would you suggest ?
> Regards,
> Lionel

Ted Dunning, CTO

111 West Evelyn Ave. Ste. 202
Sunnyvale, CA 94086
858-414-0013 (m)
408-773-0220 (fax)

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