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From "Anson Lau" <>
Subject RE: using boost factor
Date Wed, 23 Jun 2004 10:59:38 GMT
Hi guys,

It seems like to really customise the scoring in lucene, one will have to go
into the lucene source.

I spend a fair bit of time looking into this and it seems to me not the full
scoring api is exported.  The formula documented on the Similarity class
seems to explain how a term is scored, but not, for example, how the final
score on a Boolean query is computed from each individual component. (Please
correct me if I'm wrong).  Normalisation is another part where the API is
not exported.


-----Original Message-----
From: Otis Gospodnetic [] 
Sent: Wednesday, June 23, 2004 3:51 AM
To: Lucene Users List
Subject: Re: using boost factor

Hello Anson,

I would look at IndexSearcher's explain method:

This should give you insight into what's contributing to the high/low
scores, thus telling you what you can tweak.  Perhaps it's just the
boost, perhaps some other similarity factors.

Using explain should provide you information such as this, for example:

I hope this helps.  Somebody else will probably be able to give more
information, but this should get you started while you wait.


--- Anson Lau <> wrote:
> Hi guys,
> Lets say I want to search the term "hello world" over 3 fields with
> different boost:
> ((hello:field1 world:field1)^0.001 (hello:field2 world:field2)^100
> (hello:field3 world:field3)^20000))
> Note I've given field1 a really low boost, a heavy boost to field2
> and a
> REALLY heavy boost to field3.
> What is happening to me is that a term that matches both field1 and
> field2,
> will have a higher score than a term that matches field3 only, even
> though
> field3's boost is WAY higher.
> Can I change this behaviour such that the match in field3 only will
> actually
> have a higher score because of the boost?
> Thanks,
> Anson

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