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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1522) another highlighter
Date Wed, 18 Mar 2009 10:59:51 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1522?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12682987#action_12682987
] 

Michael McCandless commented on LUCENE-1522:
--------------------------------------------


OK to sum up here with observations / wish list / ideas /
controversies / etc. for Lucene's future merged highlighter:

  * Fragmenter should aim for fast "eye + brain scanning
    consumability" (eg, try hard to start on sentence boundaries,
    include context)

  * Let's try for single source -- each Query/Weight/Scorer should be
    able to enumerate the set of term positions/spans that caused it
    to match a specific doc (like explain(), but provides
    positions/spans detailing the match).  Trying to "reverse
    engineer" the matching is brittle

  * Sliding window is better than static "top down" fragmentation

  * To scale, we should make a simple IndexReader impl on top of term
    vectors, but still allow the "re-index single doc on the fly"
    option

  * Favoring breadth (more unique terms instead of many occurences of
    certain terms) seems important, except for too-many-term queries
    where this gets unwieldy

  * Prefer a single fragment if it scores well enough, but fall back
    to several, if necessary, to show "breadth"

  * Produce structured output so non-HTML front ends (eg Flex) can
    render

  * Try to include "context around the hits", when possible (eg the
    "favor middle of hte sentence" that Michael described)

  * Maybe or maybe don't let IDF affect fragment scoring

  * Performance is important -- use TermVectors if present, add early
    termination if you've already found a good enough fragdoc, etc.

  * Maybe a tree-based fragdoc enumeration / searching model; I think
    this'd be even more efficient than sliding window, especially for
    large docs

  * Multi-color, HeatMap default ootb HTML UIs are nice

  * It's all very subjective and quite a good challenge!!

In the meantime, it seems like we should commit this H2 and give users
the choice?  We can then iterate over time on our wish list....


> another highlighter
> -------------------
>
>                 Key: LUCENE-1522
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1522
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: contrib/highlighter
>            Reporter: Koji Sekiguchi
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.9
>
>         Attachments: colored-tag-sample.png, LUCENE-1522.patch, LUCENE-1522.patch
>
>
> I've written this highlighter for my project to support bi-gram token stream (general
token stream (e.g. WhitespaceTokenizer) also supported. see test code in patch). The idea
was inherited from my previous project with my colleague and LUCENE-644. This approach needs
highlight fields to be TermVector.WITH_POSITIONS_OFFSETS, but is fast and can support N-grams.
This depends on LUCENE-1448 to get refined term offsets.
> usage:
> {code:java}
> TopDocs docs = searcher.search( query, 10 );
> Highlighter h = new Highlighter();
> FieldQuery fq = h.getFieldQuery( query );
> for( ScoreDoc scoreDoc : docs.scoreDocs ){
>   // fieldName="content", fragCharSize=100, numFragments=3
>   String[] fragments = h.getBestFragments( fq, reader, scoreDoc.doc, "content", 100,
3 );
>   if( fragments != null ){
>     for( String fragment : fragments )
>       System.out.println( fragment );
>   }
> }
> {code}
> features:
> - fast for large docs
> - supports not only whitespace-based token stream, but also "fixed size" N-gram (e.g.
(2,2), not (1,3)) (can solve LUCENE-1489)
> - supports PhraseQuery, phrase-unit highlighting with slops
> {noformat}
> q="w1 w2"
> <b>w1 w2</b>
> ---------------
> q="w1 w2"~1
> <b>w1</b> w3 <b>w2</b> w3 <b>w1 w2</b>
> {noformat}
> - highlight fields need to be TermVector.WITH_POSITIONS_OFFSETS
> - easy to apply patch due to independent package (contrib/highlighter2)
> - uses Java 1.5
> - looks query boost to score fragments (currently doesn't see idf, but it should be possible)
> - pluggable FragListBuilder
> - pluggable FragmentsBuilder
> to do:
> - term positions can be unnecessary when phraseHighlight==false
> - collects performance numbers

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