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From "Doron Cohen (JIRA)" <>
Subject [jira] Commented: (LUCENE-965) Implement a state-of-the-art retrieval function in Lucene
Date Thu, 26 Jul 2007 03:12:31 GMT


Doron Cohen commented on LUCENE-965:

Thanks for contributing this Hui Fang! Very interesting.
I agree with Grant that we should be able to asses this in the context of LUCENE-836 - I hope
to finalize it pretty soon. 
I looked into the patch and read the short paper referenced and I have a few comments:

1) Interestingly this too makes use of the average document length, as discussed in
2) The current patch seem out dated comparing to trunk and also contain many changes that
are not part of the proposed improvement. You need to run "svn update" to update with trunk
(but do "svn stat -u" beforehand to see what is going to be updated and that there are no
conflicts, and bkup your code before that just in case...)
3) The AXSimilarity class itself was is not included in the patch (note that you need to "svn
add" the new files in order for "svn diff" to include these new files in the patch.
4) On first reading of the patch it seems that the avarage length is computed at search time
for each scored term... right? This is good enough for the evaluation of this Similarity function,
but for a running solution a better performance method would be required, like the one Hoss
suggested in

> Implement a state-of-the-art retrieval function in Lucene
> ---------------------------------------------------------
>                 Key: LUCENE-965
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>    Affects Versions: 2.2
>            Reporter: Hui Fang
>         Attachments: axiomaticFunction.patch
> We implemented the axiomatic retrieval function, which is a state-of-the-art retrieval
function, to 
> replace the default similarity function in Lucene. We compared the performance of these
two functions and reported the results at

> The report shows that the performance of the axiomatic retrieval function is much better
than the default function. The axiomatic retrieval function is able to find more relevant
documents and users can see more relevant documents in the top-ranked documents. Incorporating
such a state-of-the-art retrieval function could improve the search performance of all the
applications which were built upon Lucene. 
> Most changes related to the implementation are made in AXSimilarity, TermScorer and
 However, many test cases are hand coded to test whether the implementation of the default
function is correct. Thus, I also made the modification to many test files to make the new
retrieval function pass those cases. In fact, we found that some old test cases are not reasonable.
For example, in the testQueries02 of, 
> the query is "+w3 xx", and we have two documents "w1 xx w2 yy w3" and "w1 w3 xx w2 yy
> The second document should be more relevant than the first one, because it has more 
> occurrences of the query term "w3". But the original test case would require us to rank

> the first document higher than the second one, which is not reasonable. 

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