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From "Hui Fang (JIRA)" <>
Subject [jira] Commented: (LUCENE-965) Implement a state-of-the-art retrieval function in Lucene
Date Thu, 20 Aug 2009 20:08:14 GMT


Hui Fang commented on LUCENE-965:

Hello everyone, 

We have re-implemented the retrieval functions in a very different way. The main differences
are (1) the average document length will not be computed in the retrieval process as we did
the previous implementation, which could make the retrieval process more efficiently and (2)
instead of modifying the existing search related classes, we integrate the new retrieval functions
through two new classes, i.e., AXTermQuery and. AXTermScorer by extending TermQuery and TermScorer
classes.  I think that the current implementation addresses most concerns raised in this discussion

The source codes and the updated reports of our implementation is now available at
  We have implemented two slightly versions for lucene-2.4.1 and lucene-2.9-dev.   We hope
that the implementation of the axiomatic retrieval function could be integrated in the releases
of the Lucene.    Please feel free to let me know if you have any questions or comments. 


> 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
>             Fix For: 3.0
>         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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