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From AlexeyG <agorok...@z-techcorp.com>
Subject Boosting Documents and score calculation
Date Thu, 24 Aug 2006 17:06:35 GMT

Hello,

I ran into some very strange behavior by Lucene 1.9.  Boost factor under 1.3
does not effect the result score!  I wrote a simple test to isolate the
issue:

Writing test index
Creating 3 documents with same KEY and boosts of default, 1.1, 1.2, and 1.3

	public static void writeTestIndex() throws IOException {
		
		// opening index writer
		IndexWriter writer = null;
		writer = new IndexWriter("C:\\a_temp", new StandardAnalyzer(), true);
		
		Document currentDocument = null;
		
		// creating and adding document with DEFAULT boost
		currentDocument = new Document();
		currentDocument.add(new Field("KEY", "AA", Field.Store.YES,
Field.Index.UN_TOKENIZED));
		currentDocument.add(new Field("BOOST_FACTOR", "1", Field.Store.YES,
Field.Index.UN_TOKENIZED));
		writer.addDocument(currentDocument);

		// creating and adding document with 1.1 boost
		currentDocument = new Document();
		currentDocument.add(new Field("KEY", "AA", Field.Store.YES,
Field.Index.UN_TOKENIZED));
		currentDocument.add( new Field("BOOST_FACTOR", "1.1", Field.Store.YES,
Field.Index.UN_TOKENIZED));
		currentDocument.setBoost((float)1.1);
		writer.addDocument(currentDocument);

		// creating and adding document with 1.2 boost
		currentDocument = new Document();
		currentDocument.add(new Field("KEY", "AA", Field.Store.YES,
Field.Index.UN_TOKENIZED));
		currentDocument.add( new Field("BOOST_FACTOR", "1.2", Field.Store.YES,
Field.Index.UN_TOKENIZED));
		currentDocument.setBoost((float)1.2);
		writer.addDocument(currentDocument);
		
		// creating and adding document with 1.3 boost
		currentDocument = new Document();
		currentDocument.add(new Field("KEY", "AA", Field.Store.YES,
Field.Index.UN_TOKENIZED));
		currentDocument.add(new Field("BOOST_FACTOR", "1.3", Field.Store.YES,
Field.Index.UN_TOKENIZED));
		currentDocument.setBoost((float)1.3);
		writer.addDocument(currentDocument);			

		// optimizing and closing IndexWriter
		writer.optimize();
		writer.close();
	}


Test Search
Searching for the KEY value, which is the same in all 4 documents

	public static void testIndex() throws IOException {

		// opening IndexSearcher
		IndexSearcher searcher = null;
		searcher = new IndexSearcher("C:\\a_temp");

		// searching for KEY
		Hits hits = searcher.search(new TermQuery(new Term("KEY", "AA")));

		// listing documents and their BOOST_FACTOR field
		Document doc = null;
		if (null != hits) {
			logger.debug("Listing results: ");
			for (int i = 0; i < hits.length(); i++) {
				doc = hits.doc(i);
				logger.debug("BOOST_FACTOR field: " + doc.get("BOOST_FACTOR") + " Score:
" + hits.score(i));
			}
		}
		
		// closing IndexSearcher
		searcher.close();
	}

Output

BOOST_FACTOR field: 1.3 Score: 0.9710705
BOOST_FACTOR field: 1 Score: 0.7768564
BOOST_FACTOR field: 1.1 Score: 0.7768564
BOOST_FACTOR field: 1.2 Score: 0.7768564

Boost of 1.1 and 1.2 did not effect score for the last 2 documents! 
Document with boost of 1.3 jumped to the top, but the rest were returned in
the order they were added to the index.

What am I missing here?  I thought document score would reflect all levels
of boost, not just 1.3 and above?  Please help.
-- 
View this message in context: http://www.nabble.com/Boosting-Documents-and-score-calculation-tf2159899.html#a5968287
Sent from the Lucene - Java Users forum at Nabble.com.


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