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From Ken Krugler <kkrugler_li...@transpac.com>
Subject Re: Document "freshness" and Boost Functions
Date Wed, 17 Jan 2007 15:46:22 GMT
>On 1/17/07, Luis Neves <luis.neves@co.sapo.pt> wrote:
>
>>...I see that is possible to use
>>"Boost Functions" to influence the score. How would that work in order to
>>improve the score of recent documents? (I have a timestamp field in the
>>schema)...
>
>I've been using expressions like these in boolean queries, based on  a
>"broadcast_date" field:
>
>_val_:"linear(recip(rord(broadcast_date),1,1000,1000),11,0)"
>
>Where recip computes an age-based score, and linear is used to boost it.
>
>See 
>http://incubator.apache.org/solr/docs/api/org/apache/solr/search/QueryParsing.html,
>and also the list archives, these functions have been discussed
>before.
>
>I'm not sure off the top of my head how to use this with dismax 
>queries though.

There's another trick, described by Andrzej here:

http://www.gossamer-threads.com/lists/lucene/java-user/43457

You have another field such as days: where you write the same token 
(e.g. "1") the number of times that matches the age of your document 
(starting from some reasonable base date). Then add +days:1 to your 
query and Lucene winds up boosting the results by how recent they are.

-- Ken
-- 
Ken Krugler
Krugle, Inc.
+1 530-210-6378
"Find Code, Find Answers"

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