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From "Alex Vigdor (JIRA)" <>
Subject [jira] Created: (LUCENE-1822) FastVectorHighlighter: SimpleFragListBuilder hard-coded 6 char margin is too naive
Date Tue, 18 Aug 2009 22:32:14 GMT
FastVectorHighlighter: SimpleFragListBuilder hard-coded 6 char margin is too naive

                 Key: LUCENE-1822
             Project: Lucene - Java
          Issue Type: Improvement
          Components: contrib/*
    Affects Versions: 2.9
         Environment: any
            Reporter: Alex Vigdor
            Priority: Minor
         Attachments: LUCENE-1822.patch

The new FastVectorHighlighter performs extremely well, however I've found in testing that
the window of text chosen per fragment is often very poor, as it is hard coded in SimpleFragListBuilder
to always select starting 6 characters to the left of the first phrase match in a fragment.
 When selecting long fragments, this often means that there is barely any context before the
highlighted word, and lots after; even worse, when highlighting a phrase at the end of a short
text the beginning is cut off, even though the entire phrase would fit in the specified fragCharSize.
 For example, highlighting "Punishment" in "Crime and Punishment"  returns "e and <b>Punishment</b>"
no matter what fragCharSize is specified.  I am going to attach a patch that improves the
text window selection by recalculating the starting margin once all phrases in the fragment
have been identified - this way if a single word is matched in a fragment, it will appear
in the middle of the highlight, instead of 6 characters from the beginning.  This way one
can also guarantee that the entirety of short texts are represented in a fragment by specifying
a large enough fragCharSize.

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