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Hello community, dear Grant
I have build a JUnit test case that illustrates the problem -
there, I try to cut
out the right substring with the offset values given from Lucene -
and fail :(
A few remarks:
In this example, the 'é' from 'Bosé' makes that the '\w' pattern
don't matches -
it is recognized, unlike in StandardAnalyzer - as delimiter sign.
Analysis: It seems that Lucene calculates the offset values by
adding a virtual
delimiter between every field value.
But Lucene forgets the last characters of a field value when these are
analyzer-specific delimiter values. (I seem this because of
DocumentWriter, line
245: 'if(lastToken != null) offset += lastToken.endOffset() + 1;)'
With this line of code, only the end offset of the last token is
considered - by
forgetting potential, trimmed delimiter chars.
Thus, solving would be:
1. Add a single delimiter char between the field values
2. Substract (from the Lucene Offset) the count of analyzer-
specific delimiters
that are at the end of all field values before the match
For this, someone needs to know what a delimiter for an specific
analyzer is.
The other possibility of course is to change the behaviour inside
Lucene, because
the current offset values are more or less useless / hard to use (I
currently have
no idea how to get analyzer-specific delimiter chars).
For me, this looks like a bug - am I wrong?
Any ideas/hints/remarks? I would be very lucky about :)
Greetings
Christian
Grant Ingersoll schrieb:
Hi Christian,
Is there anyway you can post a complete, self-contained example
preferably as a JUnit test? I think it would be useful to know more
about how you are indexing (i.e. what Analyzer, etc.)
The offsets should be taken from whatever is set in on the Token
during
Analysis. I, too, am trying to remember where in the code this is
taking place
Also, what version of Lucene are you using?
-Grant
On Aug 16, 2007, at 5:50 AM, [EMAIL PROTECTED] wrote:
Hello,
I have an index with an 'actor' field, for each actor there exists an
single field value entry, e.g.
stored/
compressed,indexed,tokenized,termVector,termVectorOffsets,termVectorP
osition
<movie_actors>
movie_actors:Mayrata O'Wisiedo (as Mairata O'Wisiedo)
movie_actors:Miguel Bosé
movie_actors:Anna Lizaran (as Ana Lizaran)
movie_actors:Raquel Sanchís
movie_actors:Angelina Llongueras
I try to get the term offset, e.g. for 'angelina' with
termPositionVector = (TermPositionVector)
reader.getTermFreqVector(docNumber, "movie_actors");
int iTermIndex = termPositionVector.indexOf("angelina");
TermVectorOffsetInfo[] termOffsets =
termPositionVector.getOffsets(iTermIndex);
I get one TermVectorOffsetInfo for the field - with offset numbers
that are bigger than one single
Field entry.
I guessed that Lucene gives the offset number for the situation that
all values were concatenated,
which is for the single (virtual) string:
movie_actors:Mayrata O'Wisiedo (as Mairata O'Wisiedo)Miguel BoséAnna
Lizaran (as Ana Lizaran)Raquel SanchísAngelina Llongueras
This fits in nearly no situation, so my second guess was that lucene
adds some virtual delimiters between the single
field entries for offset calculation. I added a delimiter, so the
result would be:
movie_actors:Mayrata O'Wisiedo (as Mairata O'Wisiedo) Miguel Bosé
Anna
Lizaran (as Ana Lizaran) Raquel Sanchís Angelina Llongueras
(note the ' ' between each actor name)
..this also fits not for each situation - there are too much
delimiters there now, so, further, I guessed that Lucene don't add
a delimiter in each situation. So I added only one when the last
character of an entry was no alphanumerical one, with:
StringBuilder strbAttContent = new StringBuilder();
for (String strAttValue : m_luceneDocument.getValues(strFieldName))
{
strbAttContent.append(strAttValue);
if(strbAttContent.substring(strbAttContent.length() -
1).matches("\\w"))
strbAttContent.append(' ');
}
where I get the result (virtual) entry:
movie_actors:Mayrata O'Wisiedo (as Mairata O'Wisiedo)Miguel BoséAnna
Lizaran (as Ana Lizaran)Raquel Sanchís Angelina Llongueras
this fits in ~96% of all my queries....but still its not 100% the way
lucene calculates the offset value for fields with multiple
value entries.
..maybe the problem is that there are special characters inside my
database (e.g. the 'é' at 'Bosé'), where my '\w' don't matches.
I have looked to this specific situation, but considering this one
character don't solves the problem.
How do Lucene calculates these offsets? I also searched inside the
source code, but can't find the correct place.
Thanks in advance!
Christian Reuschling
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_____________________________________________________________________
_________
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Software Engineer
Knowledge Management Department
German Research Center for Artificial Intelligence DFKI GmbH
Trippstadter Straße 122, D-67663 Kaiserslautern, Germany
Phone: +49.631.20575-125
mailto:[EMAIL PROTECTED] http://www.dfki.uni-kl.de/~reuschling/
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package org.dynaq.index;
import static org.junit.Assert.assertTrue;
import java.io.IOException;
import java.util.LinkedList;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.TermPositionVector;
import org.apache.lucene.index.TermVectorOffsetInfo;
import org.apache.lucene.queryParser.ParseException;
import org.apache.lucene.queryParser.QueryParser;
import org.apache.lucene.search.Hits;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.Searcher;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.LockObtainFailedException;
import org.apache.lucene.store.RAMDirectory;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
public class TokenizerTest
{
IndexReader m_indexReader;
Analyzer m_analyzer = new StandardAnalyzer();
@Before
public void createIndex() throws CorruptIndexException,
LockObtainFailedException, IOException
{
Directory ramDirectory = new RAMDirectory();
// we create a fist little set of actors names
LinkedList<String> llActorNames = new LinkedList<String>();
llActorNames.add("Mayrata O'Wisiedo (as Mairata O'Wisiedo)");
llActorNames.add("Miguel Bosé");
llActorNames.add("Anna Lizaran (as Ana Lizaran)");
llActorNames.add("Raquel Sanchís");
llActorNames.add("Angelina Llongueras");
// store them into a single document with multiple values
for one Field
Document testDoc = new Document();
for (String strActorsName : llActorNames)
{
Field testEntry =
new Field("movie_actors", strActorsName,
Field.Store.YES, Field.Index.TOKENIZED,
Field.TermVector.WITH_POSITIONS_OFFSETS);
testDoc.add(testEntry);
}
// now we write it into the index
IndexWriter indexWriter = new IndexWriter(ramDirectory,
true, m_analyzer, true);
indexWriter.addDocument(testDoc);
indexWriter.close();
m_indexReader = IndexReader.open(ramDirectory);
}
@Test
public void checkOffsetValues() throws ParseException, IOException
{
// first, we search for 'angelina'
String strSearchTerm = "Angelina";
Searcher searcher = new IndexSearcher(m_indexReader);
QueryParser parser = new QueryParser("movie_actors",
m_analyzer);
Query query = parser.parse(strSearchTerm);
Hits hits = searcher.search(query);
Document resultDoc = hits.doc(0);
String[] straValues = resultDoc.getValues("movie_actors");
// now, we get the field values and build a single string
value out of them
StringBuilder strbSimplyConcatenated = new StringBuilder();
StringBuilder strbWithDelimiters = new StringBuilder();
StringBuilder strbWithDelimitersAfterAlphaNumChar = new
StringBuilder();
for (String strActorName : straValues)
{
// first situation: we simply concatenate all field
value entries
strbSimplyConcatenated.append(strActorName);
// second: we add a single delimiter char between the
field values
strbWithDelimiters.append(strActorName).append('$');
// third try: we add a single delimiter, but only if
the last char of the actor before was a alphanum-char
strbWithDelimitersAfterAlphaNumChar.append(strActorName);
String strLastChar = strActorName.substring
(strActorName.length() - 1, strActorName.length());
if(strLastChar.matches("\\w"))
strbWithDelimitersAfterAlphaNumChar.append('$');
}
// this is the offset value from lucene. This should be the
place of 'angelina' in one of the concatenated value Strings above
TermPositionVector termPositionVector =
(TermPositionVector) m_indexReader.getTermFreqVector(0,
"movie_actors");
int iTermIndex = termPositionVector.indexOf
(strSearchTerm.toLowerCase());
TermVectorOffsetInfo[] termOffsets =
termPositionVector.getOffsets(iTermIndex);
int iStartOffset = termOffsets[0].getStartOffset();
int iEndOffset = termOffsets[0].getEndOffset();
//we create the substrings according to the offset value
given from lucene
String strSubString1 = strbSimplyConcatenated.substring
(iStartOffset, iEndOffset);
String strSubString2 = strbWithDelimiters.substring
(iStartOffset, iEndOffset);
String strSubString3 =
strbWithDelimitersAfterAlphaNumChar.substring(iStartOffset,
iEndOffset);
System.out.println("Offset value: " + iStartOffset + "-" +
iEndOffset);
System.out.println("simply concatenated:");
System.out.println(strbSimplyConcatenated);
System.out.println("SubString for offset: '" +
strSubString1 + "'");
System.out.println();
System.out.println("with delimiters:");
System.out.println(strbWithDelimiters);
System.out.println("SubString for offset: '" +
strSubString2 + "'");
System.out.println();
System.out.println("with delimiter after alphanum
character:");
System.out.println(strbWithDelimitersAfterAlphaNumChar);
System.out.println("SubString for offset: '" +
strSubString3 + "'");
//is the offset value correct for one of the concatenated
strings?
//this fails for all situations
assertTrue(strSubString1.equals(strSearchTerm) ||
strSubString2.equals(strSearchTerm) || strSubString3.equals
(strSearchTerm));
/*
* Comments: In this example, the 'é' from 'Bosé' makes
that the '\w' pattern don't matches - it is recognized, unlike in
* StandardAnalyzer - as delimiter sign.
*
* Analysis: It seems that Lucene calculates the offset
values by adding a virtual delimiter between every field value.
* But Lucene forgets the last characters of a field value
when these are analyzer-specific delimiter values.
* (I seem this because of DocumentWriter, line 245: 'if
(lastToken != null) offset += lastToken.endOffset() + 1;)'
* With this line of code, only the end offset of the last
token is considered - by forgetting potential, trimmed delimiter
* chars.
*
* Thus, solving would be:
* 1. Add a single delimiter char between the field values
* 2. Substract (from the Lucene Offset) the count of
analyzer-specific delimiters that are at the end of all field
values before the match
*
* For this, someone needs to know what a delimiter for an
specific analyzer is.
*/
}
@After
public void closeIndex() throws CorruptIndexException, IOException
{
m_indexReader.close();
}
}
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