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package org.apache.lucene.search;
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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import java.io.IOException;
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import org.apache.lucene.index.IndexReader;
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import org.apache.lucene.search.BooleanQuery;
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import org.apache.lucene.search.DefaultSimilarity;
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import org.apache.lucene.search.Query;
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import org.apache.lucene.search.Searcher;
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import org.apache.lucene.search.Similarity;
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* The BoostingQuery class can be used to effectively demote results that match a given query.
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* Unlike the "NOT" clause, this still selects documents that contain undesirable terms,
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* but reduces their overall score:
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* Query balancedQuery = new BoostingQuery(positiveQuery, negativeQuery, 0.01f);
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* In this scenario the positiveQuery contains the mandatory, desirable criteria which is used to
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* select all matching documents, and the negativeQuery contains the undesirable elements which
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* are simply used to lessen the scores. Documents that match the negativeQuery have their score
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* multiplied by the supplied "boost" parameter, so this should be less than 1 to achieve a
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* This code was originally made available here: [WWW] http://marc.theaimsgroup.com/?l=lucene-user&m=108058407130459&w=2
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* and is documented here: http://wiki.apache.org/lucene-java/CommunityContributions
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public class BoostingQuery extends Query {
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private float boost; // the amount to boost by
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private Query match; // query to match
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private Query context; // boost when matches too
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public BoostingQuery(Query match, Query context, float boost) {
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this.context = (Query)context.clone(); // clone before boost
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this.context.setBoost(0.0f); // ignore context-only matches
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public Query rewrite(IndexReader reader) throws IOException {
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BooleanQuery result = new BooleanQuery() {
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public Similarity getSimilarity(Searcher searcher) {
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return new DefaultSimilarity() {
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public float coord(int overlap, int max) {
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case 1: // matched only one clause
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return 1.0f; // use the score as-is
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case 2: // matched both clauses
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return boost; // multiply by boost
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result.add(match, BooleanClause.Occur.MUST);
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result.add(context, BooleanClause.Occur.SHOULD);
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public int hashCode() {
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result = prime * result + Float.floatToIntBits(boost);
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result = prime * result + ((context == null) ? 0 : context.hashCode());
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result = prime * result + ((match == null) ? 0 : match.hashCode());
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public boolean equals(Object obj) {
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if (getClass() != obj.getClass())
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BoostingQuery other = (BoostingQuery) obj;
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if (Float.floatToIntBits(boost) != Float.floatToIntBits(other.boost))
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if (context == null) {
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if (other.context != null)
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} else if (!context.equals(other.context))
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if (other.match != null)
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} else if (!match.equals(other.match))
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public String toString(String field) {
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return match.toString(field) + "/" + context.toString(field);