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https://issues.apache.org/jira/browse/LUCENE-2091?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Robert Muir updated LUCENE-2091:
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Attachment: BM25SimilarityProvider.java
Hello, I think there might be a bug in the formula here.
While working on LUCENE-2392, I have implemented several formula, including
BM25 and I(Ne)C2/I(Ne)B2 from the divergence-from-randomness models.
I first implemented DFR and after verifying the relevance was correct against
published results, I noticed BM25 (with this patch) had much lower relevance
scores. This didn't make a lot of sense to me.
So I implemented BM25 from scratch, in terms of the stats framework of
LUCENE-2392.
Here are some MAP scores on an english text collection (I have tested several
and this is the consistent behavior):
|DefaultSimilarity|0.4333|
|BM25 (LUCENE-2091)|0.4131|
|BM25 (LUCENE-2392)|0.4395|
|BM25* (LUCENE-2392)|0.4401|
|DFR I(Ne)C2|0.4453|
|DFR I(Ne)B2|0.4475|
Notes:
* BM25* is what is actually attached, as it uses the flooring for IDF, but i
also tested without this (BM25)
* I used the same defaults as this patch for k1 and b parameters.
I've attached my implementation for the sake of it, although the APIs are
pretty meaningless right now, but just so you can see how I implemented the
equation.
> Add BM25 Scoring to Lucene
> --------------------------
>
> Key: LUCENE-2091
> URL: https://issues.apache.org/jira/browse/LUCENE-2091
> Project: Lucene - Java
> Issue Type: New Feature
> Components: contrib/*
> Reporter: Yuval Feinstein
> Priority: Minor
> Fix For: 3.1
>
> Attachments: BM25SimilarityProvider.java, LUCENE-2091.patch,
> persianlucene.jpg
>
> Original Estimate: 48h
> Remaining Estimate: 48h
>
> http://nlp.uned.es/~jperezi/Lucene-BM25/ describes an implementation of
> Okapi-BM25 scoring in the Lucene framework,
> as an alternative to the standard Lucene scoring (which is a version of mixed
> boolean/TFIDF).
> I have refactored this a bit, added unit tests and improved the runtime
> somewhat.
> I would like to contribute the code to Lucene under contrib.
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