Cover density ranking?

[Boris Goldowsky <bo...@alum.mit.edu>]

Since there have been a few discussions recently of overriding various
aspects of Lucene's ranking formula, I got to wondering how difficult it
might be to implement something more different from the base tf/idf
ranking system that Lucene has built in.

How difficult would it be to implement something like Cover Density
ranking for Lucene?  Has anyone tried it?  

Cover density is described at http://citeseer.ist.psu.edu/558750.html ,
and is supposed to be particularly good for short queries of the type
that you get in many web applications.

Boris



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Re: Cover density ranking?

[Doug Cutting <cu...@apache.org>]

Boris Goldowsky wrote:
> How difficult would it be to implement something like Cover Density
> ranking for Lucene?  Has anyone tried it?  
> 
> Cover density is described at http://citeseer.ist.psu.edu/558750.html ,
> and is supposed to be particularly good for short queries of the type
> that you get in many web applications.

I just glanced at the paper, so my analysis may be wrong, but I think 
one could implement cover density ranking in Lucene with spans (only in 
CVS, not in 1.3).  I think spans correspond to covers in this paper. 
But you'd need to alter SpanScorer.java to implement the cover scoring 
described in that paper.  And you'd probably need to use a custom 
Similarity implementation, which disables most other scoring (tf=1.0, 
idf=1.0, etc.), but exaggerates coordination.  Finally, you'd need to 
construct span queries.  Or something like that.

If someone tries this, please tell us how it works.

Doug

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