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https://issues.apache.org/jira/browse/LUCENE-1420?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael McCandless updated LUCENE-1420:
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Attachment: LUCENE-1420.patch
Thanks Andrzej.
I made some further changes (attached new patch):
* Changed the new Similarity.computeNorm(String, FieldInvertState)
method to return the float norm instead of setting it on the
FieldInvertState. I also removed FieldInvertState.{get,set}Norm.
* I put back the changes to SweetSpotSimilarity & MemoryIndex, but
kept the old APIs (deprecated) for back compat.
* I added {set/get}DiscountOverlaps to DefaultSimilarity, and also
overrode computeNorm to use discountOverlaps to compute the number
of tokens to pass to lengthNorm.
* The Info class is private inside MemoryIndex, even though its ctor
is public, so, I just added boolean to its ctor (ie, there's no
back-compat issue).
* Tweaked javadocs
So now, both DefaultSimilarity and SweetSpotSimilarity have the option
to discount overlaps, but do not do so by default.
> Similarity.lengthNorm and positionIncrement=0
> ---------------------------------------------
>
> Key: LUCENE-1420
> URL: https://issues.apache.org/jira/browse/LUCENE-1420
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Affects Versions: 2.3.3, 2.9
> Reporter: Andrzej Bialecki
> Assignee: Michael McCandless
> Fix For: 2.3.3, 2.9
>
> Attachments: LUCENE-1420.patch, similarity-v2.patch, similarity.patch
>
>
> Calculation of lengthNorm factor should in some cases take into account the
> number of tokens with positionIncrement=0. This should be made optional, to
> support two different scenarios:
> * when analyzers insert artificially constructed tokens into TokenStream
> (e.g. ASCII-fied versions of accented terms, stemmed terms), and it's
> unlikely that users submit queries containing both versions of tokens: in
> this case lengthNorm calculation should ignore the tokens with
> positionIncrement=0.
> * when analyzers insert synonyms, and it's likely that users may submit
> queries that contain multiple synonymous terms: in this case the lengthNorm
> should be calculated as it is now, i.e. it should take into account all terms
> no matter what is their positionIncrement.
> The default should be backward-compatible, i.e. it should count all tokens.
> (See also the discussion here: http://markmail.org/message/vfvmzrzhr6pya22h )
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