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Date: Wed, 11 Aug 2010 18:19:18 -0400 (EDT)
From: "Elmer Garduno (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
Subject: [jira] Updated: (LUCENE-2229) SimpleSpanFragmenter fails to start a
 new fragment
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     [ https://issues.apache.org/jira/browse/LUCENE-2229?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Elmer Garduno updated LUCENE-2229:
----------------------------------

     Original Estimate: 24h  (was: 72h)
    Remaining Estimate: 24h  (was: 72h)

> SimpleSpanFragmenter fails to start a new fragment
> --------------------------------------------------
>
>                 Key: LUCENE-2229
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2229
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: contrib/highlighter
>            Reporter: Elmer Garduno
>            Priority: Minor
>         Attachments: LUCENE-2229.patch
>
>   Original Estimate: 24h
>  Remaining Estimate: 24h
>
> SimpleSpanFragmenter fails to identify a new fragment when there is more than one stop word after a span is detected. This problem can be observed when the Query contains a PhraseQuery.
> The problem is that the span extends toward the end of the TokenGroup. This is because {{waitForProps = positionSpans.get(i).end + 1;}} and {{position += posIncAtt.getPositionIncrement();}} this generates a value of {{position}} greater than the value of {{waitForProps}} and {{(waitForPos == position)}} never matches.
> {code:title=SimpleSpanFragmenter.java}
>   public boolean isNewFragment() {
>     position += posIncAtt.getPositionIncrement();
>     if (waitForPos == position) {
>       waitForPos = -1;
>     } else if (waitForPos != -1) {
>       return false;
>     }
>     WeightedSpanTerm wSpanTerm = queryScorer.getWeightedSpanTerm(termAtt.term());
>     if (wSpanTerm != null) {
>       List<PositionSpan> positionSpans = wSpanTerm.getPositionSpans();
>       for (int i = 0; i < positionSpans.size(); i++) {
>         if (positionSpans.get(i).start == position) {
>           waitForPos = positionSpans.get(i).end + 1;
>           break;
>         }
>       }
>     }
>    ...
> {code}
> An example is provided in the test case for the following Document and the query *"all tokens"* followed by the words _of a_.
> {panel:title=Document}
> "Attribute instances are reused for *all tokens* _of a_ document. Thus, a TokenStream/-Filter needs to update the appropriate Attribute(s) in incrementToken(). The consumer, commonly the Lucene indexer, consumes the data in the Attributes and then calls incrementToken() again until it retuns false, which indicates that the end of the stream was reached. This means that in each call of incrementToken() a TokenStream/-Filter can safely overwrite the data in the Attribute instances."
> {panel}
> {code:title=HighlighterTest.java}
>  public void testSimpleSpanFragmenter() throws Exception {
>     ...
>     doSearching("\"all tokens\"");
>     maxNumFragmentsRequired = 2;
>     
>     scorer = new QueryScorer(query, FIELD_NAME);
>     highlighter = new Highlighter(this, scorer);
>     for (int i = 0; i < hits.totalHits; i++) {
>       String text = searcher.doc(hits.scoreDocs[i].doc).get(FIELD_NAME);
>       TokenStream tokenStream = analyzer.tokenStream(FIELD_NAME, new StringReader(text));
>       highlighter.setTextFragmenter(new SimpleSpanFragmenter(scorer, 20));
>       String result = highlighter.getBestFragments(tokenStream, text,
>           maxNumFragmentsRequired, "...");
>       System.out.println("\t" + result);
>     }
>   }
> {code}
> {panel:title=Result}
> are reused for <B>all</B> <B>tokens</B> of a document. Thus, a TokenStream/-Filter needs to update the appropriate Attribute(s) in incrementToken(). The consumer, commonly the Lucene indexer, consumes the data in the Attributes and then calls incrementToken() again until it retuns false, which indicates that the end of the stream was reached. This means that in each call of incrementToken() a TokenStream/-Filter can safely overwrite the data in the Attribute instances.
> {panel}
> {panel:title=Expected Result}
> for <B>all</B> <B>tokens</B> of a document
> {panel}

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