Does Lucene perform ranking in the retrieved set?

[Xiangyu Jin <xj...@cs.virginia.edu>]

THis might be a stupid question.

When perform retrieval for a query, deos Lucene first get
a subset of candidate matches and then perform the ranking
on the set? That is, similarity calculation is performed only
on a subset of the docuemnts to the query.

If so, from which module could I get those candidate docs,
then I can perform my own similarity calculations (since
I might need to rewrite the normalization factor, so
only modify the "similarity" model seems will not
work).

Or, is there document describe the produre of how Lucene
perform search?

thanks

xiangyu jin

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Re: Does Lucene perform ranking in the retrieved set?

[Paul Elschot <pa...@xs4all.nl>]

On Tuesday 30 November 2004 18:46, Xiangyu Jin wrote:
> 
> THis might be a stupid question.
> 
> When perform retrieval for a query, deos Lucene first get
> a subset of candidate matches and then perform the ranking
> on the set? That is, similarity calculation is performed only
> on a subset of the docuemnts to the query.

Yes, Lucene uses  an inverted index for this.

> If so, from which module could I get those candidate docs,
> then I can perform my own similarity calculations (since
> I might need to rewrite the normalization factor, so
> only modify the "similarity" model seems will not
> work).

To change the normalisation you may consider implementing
your own Weight:
http://jakarta.apache.org/lucene/docs/api/org/apache/lucene/search/Weight.html
For some example implementations of Weight the Lucene source
code in the org.apache.lucene.search package is the best resource.

Using your own Weight also requires a subclass of Query that returns
this weight in the createWeight() method.

> Or, is there document describe the produre of how Lucene
> perform search?

This describes the scoring:
http://jakarta.apache.org/lucene/docs/api/org/apache/lucene/search/Similarity.html
See also the DefaultSimilarity.

Regards,
Paul Elschot


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