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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.solr.search.similarities;
import org.apache.lucene.search.similarities.BM25Similarity;
import org.apache.lucene.search.similarities.Similarity;
import org.apache.solr.common.params.SolrParams;
import org.apache.solr.schema.SimilarityFactory;
/**
* Factory for BM25Similarity. This is the default similarity since 8.x.
* If you need the exact same formula as in 6.x and 7.x you should instead look at
* {@link LegacyBM25SimilarityFactory}
*
* Parameters:
*
* - k1 (float): Controls non-linear term frequency normalization (saturation).
* The default is
1.2
* - b (float): Controls to what degree document length normalizes tf values.
* The default is
0.75
*
*
* Optional settings:
*
* - discountOverlaps (bool): Sets
* {@link BM25Similarity#setDiscountOverlaps(boolean)}
*
* @lucene.experimental
* @since 8.0.0
*/
public class BM25SimilarityFactory extends SimilarityFactory {
private boolean discountOverlaps;
private float k1;
private float b;
@Override
public void init(SolrParams params) {
super.init(params);
discountOverlaps = params.getBool("discountOverlaps", true);
k1 = params.getFloat("k1", 1.2f);
b = params.getFloat("b", 0.75f);
}
@Override
public Similarity getSimilarity() {
BM25Similarity sim = new BM25Similarity(k1, b);
sim.setDiscountOverlaps(discountOverlaps);
return sim;
}
}