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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.Serializable;
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import java.util.ArrayList;
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/** Expert: Describes the score computation for document and query. */
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public class Explanation implements java.io.Serializable {
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private float value; // the value of this node
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private String description; // what it represents
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private ArrayList<Explanation> details; // sub-explanations
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public Explanation() {}
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public Explanation(float value, String description) {
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this.description = description;
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* Indicates whether or not this Explanation models a good match.
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* By default, an Explanation represents a "match" if the value is positive.
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public boolean isMatch() {
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return (0.0f < getValue());
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/** The value assigned to this explanation node. */
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public float getValue() { return value; }
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/** Sets the value assigned to this explanation node. */
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public void setValue(float value) { this.value = value; }
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/** A description of this explanation node. */
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public String getDescription() { return description; }
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/** Sets the description of this explanation node. */
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public void setDescription(String description) {
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this.description = description;
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* A short one line summary which should contain all high level
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* information about this Explanation, without the "Details"
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protected String getSummary() {
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return getValue() + " = " + getDescription();
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/** The sub-nodes of this explanation node. */
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public Explanation[] getDetails() {
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return details.toArray(new Explanation[0]);
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/** Adds a sub-node to this explanation node. */
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public void addDetail(Explanation detail) {
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details = new ArrayList<Explanation>();
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/** Render an explanation as text. */
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public String toString() {
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protected String toString(int depth) {
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StringBuilder buffer = new StringBuilder();
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for (int i = 0; i < depth; i++) {
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buffer.append(getSummary());
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Explanation[] details = getDetails();
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if (details != null) {
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for (int i = 0 ; i < details.length; i++) {
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buffer.append(details[i].toString(depth+1));
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return buffer.toString();
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/** Render an explanation as HTML. */
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public String toHtml() {
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StringBuilder buffer = new StringBuilder();
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buffer.append("<ul>\n");
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buffer.append("<li>");
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buffer.append(getSummary());
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buffer.append("<br />\n");
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Explanation[] details = getDetails();
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if (details != null) {
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for (int i = 0 ; i < details.length; i++) {
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buffer.append(details[i].toHtml());
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buffer.append("</li>\n");
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buffer.append("</ul>\n");
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return buffer.toString();
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* Small Util class used to pass both an idf factor as well as an
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* explanation for that factor.
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* This class will likely be held on a {@link Weight}, so be aware
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* before storing any large or un-serializable fields.
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public static abstract class IDFExplanation implements Serializable {
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* @return the idf factor
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public abstract float getIdf();
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* This should be calculated lazily if possible.
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* @return the explanation for the idf factor.
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public abstract String explain();