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Posted to dev@lucene.apache.org by "Koji Sekiguchi (JIRA)" <ji...@apache.org> on 2012/06/12 04:14:43 UTC
[jira] [Assigned] (LUCENE-4133) FastVectorHighlighter: A weighted
approach for ordered fragments
[ https://issues.apache.org/jira/browse/LUCENE-4133?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Koji Sekiguchi reassigned LUCENE-4133:
--------------------------------------
Assignee: Koji Sekiguchi
> FastVectorHighlighter: A weighted approach for ordered fragments
> ----------------------------------------------------------------
>
> Key: LUCENE-4133
> URL: https://issues.apache.org/jira/browse/LUCENE-4133
> Project: Lucene - Java
> Issue Type: Improvement
> Components: modules/highlighter
> Affects Versions: 4.0, 5.0
> Reporter: Sebastian Lutze
> Assignee: Koji Sekiguchi
> Priority: Minor
> Labels: FastVectorHighlighter
> Fix For: 4.0
>
> Attachments: LUCENE-4133.patch
>
>
> The FastVectorHighlighter currently disregards IDF-weights for matching terms within generated fragments. In the worst case, a fragment, which contains high number of very common words, is scored higher, than a fragment that contains *all* of the terms which have been used in the original query.
> This patch provides ordered fragments with IDF-weighted terms:
> *For each distinct matching term per fragment:*
> _weight = weight + IDF * boost_
> *For each fragment:*
> _weight = weight * length * 1 / sqrt( length )_
> |weight| total weight of fragment
> |IDF| inverse document frequency for each distinct matching term
> |boost| query boost as provided, for example _term^2_
> |length| total number of non-distinct matching terms per fragment
> *Method:*
> {code:java}
> public void add( int startOffset, int endOffset, List<WeightedPhraseInfo> phraseInfoList ) {
>
> float totalBoost = 0;
>
> List<SubInfo> subInfos = new ArrayList<SubInfo>();
> HashSet<String> distinctTerms = new HashSet<String>();
>
> int length = 0;
> for( WeightedPhraseInfo phraseInfo : phraseInfoList ){
> subInfos.add( new SubInfo( phraseInfo.getText(), phraseInfo.getTermsOffsets(), phraseInfo.getSeqnum() ) );
> for ( TermInfo ti : phraseInfo.getTermsInfos()) {
> if ( distinctTerms.add( ti.getText() ) )
> totalBoost += ti.getWeight() * phraseInfo.getBoost();
> length++;
> }
> }
> totalBoost *= length * ( 1 / Math.sqrt( length ) );
>
> getFragInfos().add( new WeightedFragInfo( startOffset, endOffset, subInfos, totalBoost ) );
> }
> {code}
> The ranking-formula should be the same, or at least similar, to that one used in QueryTermScorer.
> *This patch contains:*
> * a changed class-member in FieldPhraseList (termInfos to termsInfos)
> * a changed local variable in SimpleFieldFragList (score to totalBoost)
> * adds a missing @override in SimpleFragListBuilder
> * class WeightedFieldFragList, a implementation of FieldFragList
> * class WeightedFragListBuilder, a implementation of BaseFragListBuilder
> * class WeightedFragListBuilderTest, a simple test-case
> * updated docs for FVH
> Last part (see also LUCENE-4091, LUCENE-4107, LUCENE-4113) of LUCENE-3440.
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