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https://issues.apache.org/jira/browse/DERBY-6564?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13993698#comment-13993698
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Rick Hillegas commented on DERBY-6564:
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Hi Kim,
Thanks for asking these questions. They have caused me to think a little more
deeply about the meaning of score and scoreCeiling. I think I need to change
the api a little.
CH> score – what are the minimum and maximum values? is it like a percent (0 to
100)? or 0 to 1.0?
CH>
I don't think there is a minimum or maximum score. The only contract is that
higher scores indicate a better match. Some googling suggest that scores can
even be negative. See, for instance,
http://stackoverflow.com/questions/8918224/what-is-the-maximum-value-of-a-lucene-score
CH> keycolumns – comma-separated list, I gather?
CH>
Right. Its a vararg, a variable length (possibly empty) comma-separated list.
CH> Under "Querying an index", a line in the returned table says
CH> DOCUMENT ID INT,
CH> This is supposed to be
CH> DOCUMENTID INT,
CH> isn't it?
CH>
Right. Sorry about that.
CH> I thought with a score the higher values indicated a better
CH> match. So why would you only want to return results with scores under
CH> a certain value (SCORECEILING)?
This is how you page through blocks of Lucene results. Let's compare this to
the SQL LIMIT/OFFSET clause. In SQL, you can use LIMIT/OFFSET to say "start at
the nth row and give me the next m results". With Lucene you say "start at
score n and give me the next m results".
CH> And what would specifying a SCORECEILING of 0 do? I thought it would
produce no results.
CH>
I need to fix this. Right now the plugin treats 0 as a special value meaning
"no scoreCeiling, start from the top". I want to change this so that 0 is just
another score value and, instead, use null to mean "no scoreCeiling, start from
the top". Thanks for bringing this up!
CH> Under "Classpath" – Where do you get the Lucene jars?
A version of Lucene is checked into the Derby source tree. The three jars you
need are in tools/java. They are the 4.7.1 Lucene jars. You can get other
versions from the Lucene website at http://lucene.apache.org/core/.
Thanks!
-Rick
> Document the experimental, optional LuceneSupport tool.
> -------------------------------------------------------
>
> Key: DERBY-6564
> URL: https://issues.apache.org/jira/browse/DERBY-6564
> Project: Derby
> Issue Type: Improvement
> Components: Documentation
> Affects Versions: 10.11.0.0
> Reporter: Rick Hillegas
> Assignee: Kim Haase
>
> The LucenePlugin.html functional spec attached to DERBY-590 has been updated.
> This feature is ready to be documented. Thanks.
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