package org.apache.lucene.search;
/**
* Copyright 2004 The Apache Software Foundation
*
* Licensed 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.
*/
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
/**
* A query that generates the union of documents produced by its subqueries, and that scores each document with the maximum
* score for that document as produced by any subquery, plus a tie breaking increment for any additional matching subqueries.
* This is useful when searching for a word in multiple fields with different boost factors (so that the fields cannot be
* combined equivalently into a single search field). We want the primary score to be the one associated with the highest boost,
* not the sum of the field scores (as BooleanQuery would give).
* If the query is "albino elephant" this ensures that "albino" matching one field and "elephant" matching
* another gets a higher score than "albino" matching both fields.
* To get this result, use both BooleanQuery and DisjunctionMaxQuery: for each term a DisjunctionMaxQuery searches for it in
* each field, while the set of these DisjunctionMaxQuery's is combined into a BooleanQuery.
* The tie breaker capability allows results that include the same term in multiple fields to be judged better than results that
* include this term in only the best of those multiple fields, without confusing this with the better case of two different terms
* in the multiple fields.
*/
public class DisjunctionMaxQuery extends Query implements Iterable<Query> {
/* The subqueries */
private ArrayList<Query> disjuncts = new ArrayList<Query>();
/* Multiple of the non-max disjunct scores added into our final score. Non-zero values support tie-breaking. */
private float tieBreakerMultiplier = 0.0f;
/** Creates a new empty DisjunctionMaxQuery. Use add() to add the subqueries.
* @param tieBreakerMultiplier the score of each non-maximum disjunct for a document is multiplied by this weight
* and added into the final score. If non-zero, the value should be small, on the order of 0.1, which says that
* 10 occurrences of word in a lower-scored field that is also in a higher scored field is just as good as a unique
* word in the lower scored field (i.e., one that is not in any higher scored field.
*/
public DisjunctionMaxQuery(float tieBreakerMultiplier) {
this.tieBreakerMultiplier = tieBreakerMultiplier;
}
/**
* Creates a new DisjunctionMaxQuery
* @param disjuncts a Collection<Query> of all the disjuncts to add
* @param tieBreakerMultiplier the weight to give to each matching non-maximum disjunct
*/
public DisjunctionMaxQuery(Collection<Query> disjuncts, float tieBreakerMultiplier) {
this.tieBreakerMultiplier = tieBreakerMultiplier;
add(disjuncts);
}
/** Add a subquery to this disjunction
* @param query the disjunct added
*/
public void add(Query query) {
disjuncts.add(query);
}
/** Add a collection of disjuncts to this disjunction
* via Iterable<Query>
*/
public void add(Collection<Query> disjuncts) {
this.disjuncts.addAll(disjuncts);
}
/** An Iterator<Query> over the disjuncts */
public Iterator<Query> iterator() {
return disjuncts.iterator();
}
/**
* Expert: the Weight for DisjunctionMaxQuery, used to
* normalize, score and explain these queries.
*
* <p>NOTE: this API and implementation is subject to
* change suddenly in the next release.</p>
*/
protected class DisjunctionMaxWeight extends Weight {
/** The Similarity implementation. */
protected Similarity similarity;
/** The Weights for our subqueries, in 1-1 correspondence with disjuncts */
protected ArrayList<Weight> weights = new ArrayList<Weight>(); // The Weight's for our subqueries, in 1-1 correspondence with disjuncts
/* Construct the Weight for this Query searched by searcher. Recursively construct subquery weights. */
public DisjunctionMaxWeight(Searcher searcher) throws IOException {
this.similarity = searcher.getSimilarity();
for (Query disjunctQuery : disjuncts) {
weights.add(disjunctQuery.createWeight(searcher));
}
}
/* Return our associated DisjunctionMaxQuery */
@Override
public Query getQuery() { return DisjunctionMaxQuery.this; }
/* Return our boost */
@Override
public float getValue() { return getBoost(); }
/* Compute the sub of squared weights of us applied to our subqueries. Used for normalization. */
@Override
public float sumOfSquaredWeights() throws IOException {
float max = 0.0f, sum = 0.0f;
for (Weight currentWeight : weights) {
float sub = currentWeight.sumOfSquaredWeights();
sum += sub;
max = Math.max(max, sub);
}
float boost = getBoost();
return (((sum - max) * tieBreakerMultiplier * tieBreakerMultiplier) + max) * boost * boost;
}
/* Apply the computed normalization factor to our subqueries */
@Override
public void normalize(float norm) {
norm *= getBoost(); // Incorporate our boost
for (Weight wt : weights) {
wt.normalize(norm);
}
}
/* Create the scorer used to score our associated DisjunctionMaxQuery */
@Override
public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder,
boolean topScorer) throws IOException {
Scorer[] scorers = new Scorer[weights.size()];
int idx = 0;
for (Weight w : weights) {
Scorer subScorer = w.scorer(reader, true, false);
if (subScorer != null && subScorer.nextDoc() != DocIdSetIterator.NO_MORE_DOCS) {
scorers[idx++] = subScorer;
}
}
if (idx == 0) return null; // all scorers did not have documents
DisjunctionMaxScorer result = new DisjunctionMaxScorer(tieBreakerMultiplier, similarity, scorers, idx);
return result;
}
/* Explain the score we computed for doc */
@Override
public Explanation explain(IndexReader reader, int doc) throws IOException {
if (disjuncts.size() == 1) return weights.get(0).explain(reader,doc);
ComplexExplanation result = new ComplexExplanation();
float max = 0.0f, sum = 0.0f;
result.setDescription(tieBreakerMultiplier == 0.0f ? "max of:" : "max plus " + tieBreakerMultiplier + " times others of:");
for (Weight wt : weights) {
Explanation e = wt.explain(reader, doc);
if (e.isMatch()) {
result.setMatch(Boolean.TRUE);
result.addDetail(e);
sum += e.getValue();
max = Math.max(max, e.getValue());
}
}
result.setValue(max + (sum - max) * tieBreakerMultiplier);
return result;
}
} // end of DisjunctionMaxWeight inner class
/* Create the Weight used to score us */
@Override
public Weight createWeight(Searcher searcher) throws IOException {
return new DisjunctionMaxWeight(searcher);
}
/** Optimize our representation and our subqueries representations
* @param reader the IndexReader we query
* @return an optimized copy of us (which may not be a copy if there is nothing to optimize) */
@Override
public Query rewrite(IndexReader reader) throws IOException {
int numDisjunctions = disjuncts.size();
if (numDisjunctions == 1) {
Query singleton = disjuncts.get(0);
Query result = singleton.rewrite(reader);
if (getBoost() != 1.0f) {
if (result == singleton) result = (Query)result.clone();
result.setBoost(getBoost() * result.getBoost());
}
return result;
}
DisjunctionMaxQuery clone = null;
for (int i = 0 ; i < numDisjunctions; i++) {
Query clause = disjuncts.get(i);
Query rewrite = clause.rewrite(reader);
if (rewrite != clause) {
if (clone == null) clone = (DisjunctionMaxQuery)this.clone();
clone.disjuncts.set(i, rewrite);
}
}
if (clone != null) return clone;
else return this;
}
/** Create a shallow copy of us -- used in rewriting if necessary
* @return a copy of us (but reuse, don't copy, our subqueries) */
@Override @SuppressWarnings("unchecked")
public Object clone() {
DisjunctionMaxQuery clone = (DisjunctionMaxQuery)super.clone();
clone.disjuncts = (ArrayList<Query>) this.disjuncts.clone();
return clone;
}
// inherit javadoc
@Override
public void extractTerms(Set<Term> terms) {
for (Query query : disjuncts) {
query.extractTerms(terms);
}
}
/** Prettyprint us.
* @param field the field to which we are applied
* @return a string that shows what we do, of the form "(disjunct1 | disjunct2 | ... | disjunctn)^boost"
*/
@Override
public String toString(String field) {
StringBuilder buffer = new StringBuilder();
buffer.append("(");
int numDisjunctions = disjuncts.size();
for (int i = 0 ; i < numDisjunctions; i++) {
Query subquery = disjuncts.get(i);
if (subquery instanceof BooleanQuery) { // wrap sub-bools in parens
buffer.append("(");
buffer.append(subquery.toString(field));
buffer.append(")");
}
else buffer.append(subquery.toString(field));
if (i != numDisjunctions-1) buffer.append(" | ");
}
buffer.append(")");
if (tieBreakerMultiplier != 0.0f) {
buffer.append("~");
buffer.append(tieBreakerMultiplier);
}
if (getBoost() != 1.0) {
buffer.append("^");
buffer.append(getBoost());
}
return buffer.toString();
}
/** Return true iff we represent the same query as o
* @param o another object
* @return true iff o is a DisjunctionMaxQuery with the same boost and the same subqueries, in the same order, as us
*/
@Override
public boolean equals(Object o) {
if (! (o instanceof DisjunctionMaxQuery) ) return false;
DisjunctionMaxQuery other = (DisjunctionMaxQuery)o;
return this.getBoost() == other.getBoost()
&& this.tieBreakerMultiplier == other.tieBreakerMultiplier
&& this.disjuncts.equals(other.disjuncts);
}
/** Compute a hash code for hashing us
* @return the hash code
*/
@Override
public int hashCode() {
return Float.floatToIntBits(getBoost())
+ Float.floatToIntBits(tieBreakerMultiplier)
+ disjuncts.hashCode();
}
}