Xapian discuss - Mar 2007 - scoring question

Hi All

I have just realized that if I set a query like
'green jelly bean'

xapian will turn that query into
'green OR jelly OR bean'

This causes documents containing just one of the words to be considered 
a 100% hit.
The behavior I would like to see is that each word gives a 33.3% hit, so 
that a document containing all 3 words gets placed above a document with 
only 1 or 2 words in it.

I don't see an operation matching this in the query class doc. Am I just 
being blind or is there really no simple way to do this operation in xapian?

Thanks
Alec

On Tue, Mar 20, 2007 at 06:05:31PM -0700, Alexander Lind
wrote:
> I have just realized that if I set a query like
> 'green jelly bean'
> 
> xapian will turn that query into
> 'green OR jelly OR bean'
By default - you can set the default operator to "AND" with
Xapian::QueryParser::set_default_op().
> This causes documents containing just one of the words to be considered 
> a 100% hit.
It shouldn't do (unless you're using the BoolWeight weighting scheme or
a similar user defined weighting scheme).
> The behavior I would like to see is that each word gives a 33.3% hit, so 
> that a document containing all 3 words gets placed above a document with 
> only 1 or 2 words in it.
This is roughly what should happen.  The actual score from each word is
determined by considering the frequencies of the terms in the collection
and the document, and looking at document lengths, so it generally won't
be 33.3%.  If you really want exactly that, it could be achieved with a
user defined weighting scheme.

If you're really getting 100% for a document only matching one term of
a multi-term query, can you provide a small test case?

Cheers,
    Olly