package org.apache.lucene.search;
/**
* 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.
*/
import java.io.IOException;
import java.io.Serializable;
import org.apache.lucene.index.IndexReader;
/**
* Expert: Calculate query weights and build query scorers.
* <p>
* The purpose of {@link Weight} is to ensure searching does not
* modify a {@link Query}, so that a {@link Query} instance can be reused. <br>
* {@link Searcher} dependent state of the query should reside in the
* {@link Weight}. <br>
* {@link IndexReader} dependent state should reside in the {@link Scorer}.
* <p>
* A <code>Weight</code> is used in the following way:
* <ol>
* <li>A <code>Weight</code> is constructed by a top-level query, given a
* <code>Searcher</code> ({@link Query#createWeight(Searcher)}).
* <li>The {@link #sumOfSquaredWeights()} method is called on the
* <code>Weight</code> to compute the query normalization factor
* {@link Similarity#queryNorm(float)} of the query clauses contained in the
* query.
* <li>The query normalization factor is passed to {@link #normalize(float)}. At
* this point the weighting is complete.
* <li>A <code>Scorer</code> is constructed by {@link #scorer(IndexReader,boolean,boolean)}.
* </ol>
*
* @since 2.9
*/
public abstract class Weight implements Serializable {
/**
* An explanation of the score computation for the named document.
*
* @param reader sub-reader containing the give doc
* @param doc
* @return an Explanation for the score
* @throws IOException
*/
public abstract Explanation explain(IndexReader reader, int doc) throws IOException;
/** The query that this concerns. */
public abstract Query getQuery();
/** The weight for this query. */
public abstract float getValue();
/** Assigns the query normalization factor to this. */
public abstract void normalize(float norm);
/**
* Returns a {@link Scorer} which scores documents in/out-of order according
* to <code>scoreDocsInOrder</code>.
* <p>
* <b>NOTE:</b> even if <code>scoreDocsInOrder</code> is false, it is
* recommended to check whether the returned <code>Scorer</code> indeed scores
* documents out of order (i.e., call {@link #scoresDocsOutOfOrder()}), as
* some <code>Scorer</code> implementations will always return documents
* in-order.<br>
* <b>NOTE:</b> null can be returned if no documents will be scored by this
* query.
*
* @param reader
* the {@link IndexReader} for which to return the {@link Scorer}.
* @param scoreDocsInOrder
* specifies whether in-order scoring of documents is required. Note
* that if set to false (i.e., out-of-order scoring is required),
* this method can return whatever scoring mode it supports, as every
* in-order scorer is also an out-of-order one. However, an
* out-of-order scorer may not support {@link Scorer#nextDoc()}
* and/or {@link Scorer#advance(int)}, therefore it is recommended to
* request an in-order scorer if use of these methods is required.
* @param topScorer
* if true, {@link Scorer#score(Collector)} will be called; if false,
* {@link Scorer#nextDoc()} and/or {@link Scorer#advance(int)} will
* be called.
* @return a {@link Scorer} which scores documents in/out-of order.
* @throws IOException
*/
public abstract Scorer scorer(IndexReader reader, boolean scoreDocsInOrder,
boolean topScorer) throws IOException;
/** The sum of squared weights of contained query clauses. */
public abstract float sumOfSquaredWeights() throws IOException;
/**
* Returns true iff this implementation scores docs only out of order. This
* method is used in conjunction with {@link Collector}'s
* {@link Collector#acceptsDocsOutOfOrder() acceptsDocsOutOfOrder} and
* {@link #scorer(org.apache.lucene.index.IndexReader, boolean, boolean)} to
* create a matching {@link Scorer} instance for a given {@link Collector}, or
* vice versa.
* <p>
* <b>NOTE:</b> the default implementation returns <code>false</code>, i.e.
* the <code>Scorer</code> scores documents in-order.
*/
public boolean scoresDocsOutOfOrder() { return false; }
}