FastVectorHighlighter: IDF-weighted terms for ordered fragments
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Key: LUCENE-3440
URL: https://issues.apache.org/jira/browse/LUCENE-3440
Project: Lucene - Java
Issue Type: Improvement
Components: modules/highlighter
Affects Versions: 3.5
Reporter: S.L.
Priority: Minor
Fix For: 3.5
The FastVectorHighlighter uses for every term found in a fragment an equal
weight, which causes a higher ranking for fragments with a high number of words
or, in the worst case, a high number of very common words than fragments that
contains *all* of the terms used in the original query.
This patch provides ordered fragments with IDF-weighted terms:
total weight = total weight + IDF for unique term per fragment * boost of
query;
The ranking-formular should be the same, or at least similar, to that one used
in org.apache.lucene.search.highlight.QueryTermScorer.
The patch is simple, but it works for us.
Some ideas:
- A better approach would be moving the whole fragments-scoring into a separate
class.
- Switch scoring via parameter
- Exact phrases should be given a even better score, regardless if a
phrase-query was executed or not
- edismax/dismax-parameters pf, ps and pf^boost should be observed and
corresponding fragments should be ranked higher
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