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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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| |
| /** |
| * Code to search indices. |
| * |
| * <h2>Table Of Contents</h2> |
| * <ol> |
| * <li><a href="#search">Search Basics</a></li> |
| * <li><a href="#query">The Query Classes</a></li> |
| * <li><a href="#scoring">Scoring: Introduction</a></li> |
| * <li><a href="#scoringBasics">Scoring: Basics</a></li> |
| * <li><a href="#changingScoring">Changing the Scoring</a></li> |
| * <li><a href="#algorithm">Appendix: Search Algorithm</a></li> |
| * </ol> |
| * |
| * |
| * <a name="search"></a> |
| * <h2>Search Basics</h2> |
| * <p> |
| * Lucene offers a wide variety of {@link org.apache.lucene.search.Query} implementations, most of which are in |
| * this package, its subpackage ({@link org.apache.lucene.search.spans spans}, |
| * or the <a href="{@docRoot}/../queries/overview-summary.html">queries module</a>. These implementations can be combined in a wide |
| * variety of ways to provide complex querying capabilities along with information about where matches took place in the document |
| * collection. The <a href="#query">Query Classes</a> section below highlights some of the more important Query classes. For details |
| * on implementing your own Query class, see <a href="#customQueriesExpert">Custom Queries -- Expert Level</a> below. |
| * <p> |
| * To perform a search, applications usually call {@link |
| * org.apache.lucene.search.IndexSearcher#search(Query,int)}. |
| * <p> |
| * Once a Query has been created and submitted to the {@link org.apache.lucene.search.IndexSearcher IndexSearcher}, the scoring |
| * process begins. After some infrastructure setup, control finally passes to the {@link org.apache.lucene.search.Weight Weight} |
| * implementation and its {@link org.apache.lucene.search.Scorer Scorer} or {@link org.apache.lucene.search.BulkScorer BulkScorer} |
| * instances. See the <a href="#algorithm">Algorithm</a> section for more notes on the process. |
| * <!-- FILL IN MORE HERE --> |
| * <!-- TODO: this page over-links the same things too many times --> |
| * |
| * |
| * <a name="query"></a> |
| * <h2>Query Classes</h2> |
| * <h3> |
| * {@link org.apache.lucene.search.TermQuery TermQuery} |
| * </h3> |
| * |
| * <p>Of the various implementations of |
| * {@link org.apache.lucene.search.Query Query}, the |
| * {@link org.apache.lucene.search.TermQuery TermQuery} |
| * is the easiest to understand and the most often used in applications. A |
| * {@link org.apache.lucene.search.TermQuery TermQuery} matches all the documents that contain the |
| * specified |
| * {@link org.apache.lucene.index.Term Term}, |
| * which is a word that occurs in a certain |
| * {@link org.apache.lucene.document.Field Field}. |
| * Thus, a {@link org.apache.lucene.search.TermQuery TermQuery} identifies and scores all |
| * {@link org.apache.lucene.document.Document Document}s that have a |
| * {@link org.apache.lucene.document.Field Field} with the specified string in it. |
| * Constructing a {@link org.apache.lucene.search.TermQuery TermQuery} |
| * is as simple as: |
| * <pre class="prettyprint"> |
| * TermQuery tq = new TermQuery(new Term("fieldName", "term")); |
| * </pre>In this example, the {@link org.apache.lucene.search.Query Query} identifies all |
| * {@link org.apache.lucene.document.Document Document}s that have the |
| * {@link org.apache.lucene.document.Field Field} named <tt>"fieldName"</tt> |
| * containing the word <tt>"term"</tt>. |
| * <h3> |
| * {@link org.apache.lucene.search.BooleanQuery BooleanQuery} |
| * </h3> |
| * |
| * <p>Things start to get interesting when one combines multiple |
| * {@link org.apache.lucene.search.TermQuery TermQuery} instances into a |
| * {@link org.apache.lucene.search.BooleanQuery BooleanQuery}. |
| * A {@link org.apache.lucene.search.BooleanQuery BooleanQuery} contains multiple |
| * {@link org.apache.lucene.search.BooleanClause BooleanClause}s, |
| * where each clause contains a sub-query ({@link org.apache.lucene.search.Query Query} |
| * instance) and an operator (from |
| * {@link org.apache.lucene.search.BooleanClause.Occur BooleanClause.Occur}) |
| * describing how that sub-query is combined with the other clauses: |
| * <ol> |
| * |
| * <li><p>{@link org.apache.lucene.search.BooleanClause.Occur#SHOULD SHOULD} — Use this operator when a clause can occur in the result set, but is not required. |
| * If a query is made up of all SHOULD clauses, then every document in the result |
| * set matches at least one of these clauses.</p></li> |
| * |
| * <li><p>{@link org.apache.lucene.search.BooleanClause.Occur#MUST MUST} — Use this operator when a clause is required to occur in the result set and should |
| * contribute to the score. Every document in the result set will match all such clauses.</p></li> |
| * |
| * <li><p>{@link org.apache.lucene.search.BooleanClause.Occur#FILTER FILTER} — Use this operator when a clause is required to occur in the result set but |
| * should not contribute to the score. Every document in the result set will match all such clauses.</p></li> |
| * |
| * <li><p>{@link org.apache.lucene.search.BooleanClause.Occur#MUST_NOT MUST NOT} — Use this operator when a |
| * clause must not occur in the result set. No |
| * document in the result set will match |
| * any such clauses.</p></li> |
| * </ol> |
| * Boolean queries are constructed by adding two or more |
| * {@link org.apache.lucene.search.BooleanClause BooleanClause} |
| * instances. If too many clauses are added, a {@link org.apache.lucene.search.BooleanQuery.TooManyClauses TooManyClauses} |
| * exception will be thrown during searching. This most often occurs |
| * when a {@link org.apache.lucene.search.Query Query} |
| * is rewritten into a {@link org.apache.lucene.search.BooleanQuery BooleanQuery} with many |
| * {@link org.apache.lucene.search.TermQuery TermQuery} clauses, |
| * for example by {@link org.apache.lucene.search.WildcardQuery WildcardQuery}. |
| * The default setting for the maximum number |
| * of clauses is 1024, but this can be changed via the |
| * static method {@link org.apache.lucene.search.BooleanQuery#setMaxClauseCount(int)}. |
| * |
| * <h3>Phrases</h3> |
| * |
| * <p>Another common search is to find documents containing certain phrases. This |
| * is handled three different ways: |
| * <ol> |
| * <li> |
| * <p>{@link org.apache.lucene.search.PhraseQuery PhraseQuery} |
| * — Matches a sequence of |
| * {@link org.apache.lucene.index.Term Term}s. |
| * {@link org.apache.lucene.search.PhraseQuery PhraseQuery} uses a slop factor to determine |
| * how many positions may occur between any two terms in the phrase and still be considered a match. |
| * The slop is 0 by default, meaning the phrase must match exactly.</p> |
| * </li> |
| * <li> |
| * <p>{@link org.apache.lucene.search.MultiPhraseQuery MultiPhraseQuery} |
| * — A more general form of PhraseQuery that accepts multiple Terms |
| * for a position in the phrase. For example, this can be used to perform phrase queries that also |
| * incorporate synonyms. |
| * </li> |
| * <li> |
| * <p>{@link org.apache.lucene.search.spans.SpanNearQuery SpanNearQuery} |
| * — Matches a sequence of other |
| * {@link org.apache.lucene.search.spans.SpanQuery SpanQuery} |
| * instances. {@link org.apache.lucene.search.spans.SpanNearQuery SpanNearQuery} allows for |
| * much more |
| * complicated phrase queries since it is constructed from other |
| * {@link org.apache.lucene.search.spans.SpanQuery SpanQuery} |
| * instances, instead of only {@link org.apache.lucene.search.TermQuery TermQuery} |
| * instances.</p> |
| * </li> |
| * </ol> |
| * |
| * <h3> |
| * {@link org.apache.lucene.search.PointRangeQuery PointRangeQuery} |
| * </h3> |
| * |
| * <p>The |
| * {@link org.apache.lucene.search.PointRangeQuery PointRangeQuery} |
| * matches all documents that occur in a numeric range. |
| * For PointRangeQuery to work, you must index the values |
| * using a one of the numeric fields ({@link org.apache.lucene.document.IntPoint IntPoint}, |
| * {@link org.apache.lucene.document.LongPoint LongPoint}, {@link org.apache.lucene.document.FloatPoint FloatPoint}, |
| * or {@link org.apache.lucene.document.DoublePoint DoublePoint}). |
| * |
| * <h3> |
| * {@link org.apache.lucene.search.PrefixQuery PrefixQuery}, |
| * {@link org.apache.lucene.search.WildcardQuery WildcardQuery}, |
| * {@link org.apache.lucene.search.RegexpQuery RegexpQuery} |
| * </h3> |
| * |
| * <p>While the |
| * {@link org.apache.lucene.search.PrefixQuery PrefixQuery} |
| * has a different implementation, it is essentially a special case of the |
| * {@link org.apache.lucene.search.WildcardQuery WildcardQuery}. |
| * The {@link org.apache.lucene.search.PrefixQuery PrefixQuery} allows an application |
| * to identify all documents with terms that begin with a certain string. The |
| * {@link org.apache.lucene.search.WildcardQuery WildcardQuery} generalizes this by allowing |
| * for the use of <tt>*</tt> (matches 0 or more characters) and <tt>?</tt> (matches exactly one character) wildcards. |
| * Note that the {@link org.apache.lucene.search.WildcardQuery WildcardQuery} can be quite slow. Also |
| * note that |
| * {@link org.apache.lucene.search.WildcardQuery WildcardQuery} should |
| * not start with <tt>*</tt> and <tt>?</tt>, as these are extremely slow. |
| * Some QueryParsers may not allow this by default, but provide a <code>setAllowLeadingWildcard</code> method |
| * to remove that protection. |
| * The {@link org.apache.lucene.search.RegexpQuery RegexpQuery} is even more general than WildcardQuery, |
| * allowing an application to identify all documents with terms that match a regular expression pattern. |
| * <h3> |
| * {@link org.apache.lucene.search.FuzzyQuery FuzzyQuery} |
| * </h3> |
| * |
| * <p>A |
| * {@link org.apache.lucene.search.FuzzyQuery FuzzyQuery} |
| * matches documents that contain terms similar to the specified term. Similarity is |
| * determined using |
| * <a href="http://en.wikipedia.org/wiki/Levenshtein_distance">Levenshtein distance</a>. |
| * This type of query can be useful when accounting for spelling variations in the collection. |
| * |
| * |
| * <a name="scoring"></a> |
| * <h2>Scoring — Introduction</h2> |
| * <p>Lucene scoring is the heart of why we all love Lucene. It is blazingly fast and it hides |
| * almost all of the complexity from the user. In a nutshell, it works. At least, that is, |
| * until it doesn't work, or doesn't work as one would expect it to work. Then we are left |
| * digging into Lucene internals or asking for help on |
| * <a href="mailto:java-user@lucene.apache.org">java-user@lucene.apache.org</a> to figure out |
| * why a document with five of our query terms scores lower than a different document with |
| * only one of the query terms. |
| * <p>While this document won't answer your specific scoring issues, it will, hopefully, point you |
| * to the places that can help you figure out the <i>what</i> and <i>why</i> of Lucene scoring. |
| * <p>Lucene scoring supports a number of pluggable information retrieval |
| * <a href="http://en.wikipedia.org/wiki/Information_retrieval#Model_types">models</a>, including: |
| * <ul> |
| * <li><a href="http://en.wikipedia.org/wiki/Vector_Space_Model">Vector Space Model (VSM)</a></li> |
| * <li><a href="http://en.wikipedia.org/wiki/Probabilistic_relevance_model">Probabilistic Models</a> such as |
| * <a href="http://en.wikipedia.org/wiki/Probabilistic_relevance_model_(BM25)">Okapi BM25</a> and |
| * <a href="http://en.wikipedia.org/wiki/Divergence-from-randomness_model">DFR</a></li> |
| * <li><a href="http://en.wikipedia.org/wiki/Language_model">Language models</a></li> |
| * </ul> |
| * These models can be plugged in via the {@link org.apache.lucene.search.similarities Similarity API}, |
| * and offer extension hooks and parameters for tuning. In general, Lucene first finds the documents |
| * that need to be scored based on boolean logic in the Query specification, and then ranks this subset of |
| * matching documents via the retrieval model. For some valuable references on VSM and IR in general refer to |
| * <a href="http://wiki.apache.org/lucene-java/InformationRetrieval">Lucene Wiki IR references</a>. |
| * <p>The rest of this document will cover <a href="#scoringBasics">Scoring basics</a> and explain how to |
| * change your {@link org.apache.lucene.search.similarities.Similarity Similarity}. Next, it will cover |
| * ways you can customize the lucene internals in |
| * <a href="#customQueriesExpert">Custom Queries -- Expert Level</a>, which gives details on |
| * implementing your own {@link org.apache.lucene.search.Query Query} class and related functionality. |
| * Finally, we will finish up with some reference material in the <a href="#algorithm">Appendix</a>. |
| * |
| * |
| * <a name="scoringBasics"></a> |
| * <h2>Scoring — Basics</h2> |
| * <p>Scoring is very much dependent on the way documents are indexed, so it is important to understand |
| * indexing. (see <a href="{@docRoot}/overview-summary.html#overview_description">Lucene overview</a> |
| * before continuing on with this section) Be sure to use the useful |
| * {@link org.apache.lucene.search.IndexSearcher#explain(org.apache.lucene.search.Query, int) IndexSearcher.explain(Query, doc)} |
| * to understand how the score for a certain matching document was |
| * computed. |
| * |
| * <p>Generally, the Query determines which documents match (a binary |
| * decision), while the Similarity determines how to assign scores to |
| * the matching documents. |
| * |
| * </p> |
| * <h3>Fields and Documents</h3> |
| * <p>In Lucene, the objects we are scoring are {@link org.apache.lucene.document.Document Document}s. |
| * A Document is a collection of {@link org.apache.lucene.document.Field Field}s. Each Field has |
| * {@link org.apache.lucene.document.FieldType semantics} about how it is created and stored |
| * ({@link org.apache.lucene.document.FieldType#tokenized() tokenized}, |
| * {@link org.apache.lucene.document.FieldType#stored() stored}, etc). It is important to note that |
| * Lucene scoring works on Fields and then combines the results to return Documents. This is |
| * important because two Documents with the exact same content, but one having the content in two |
| * Fields and the other in one Field may return different scores for the same query due to length |
| * normalization. |
| * <h3>Score Boosting</h3> |
| * <p>Lucene allows influencing the score contribution of various parts of the query by wrapping with |
| * {@link org.apache.lucene.search.BoostQuery}.</p> |
| * |
| * <a name="changingScoring"></a> |
| * <h2>Changing Scoring — Similarity</h2> |
| * <h3>Changing the scoring formula</h3> |
| * <p> |
| * Changing {@link org.apache.lucene.search.similarities.Similarity Similarity} is an easy way to |
| * influence scoring, this is done at index-time with |
| * {@link org.apache.lucene.index.IndexWriterConfig#setSimilarity(org.apache.lucene.search.similarities.Similarity) |
| * IndexWriterConfig.setSimilarity(Similarity)} and at query-time with |
| * {@link org.apache.lucene.search.IndexSearcher#setSimilarity(org.apache.lucene.search.similarities.Similarity) |
| * IndexSearcher.setSimilarity(Similarity)}. Be sure to use the same |
| * Similarity at query-time as at index-time (so that norms are |
| * encoded/decoded correctly); Lucene makes no effort to verify this. |
| * <p> |
| * You can influence scoring by configuring a different built-in Similarity implementation, or by tweaking its |
| * parameters, subclassing it to override behavior. Some implementations also offer a modular API which you can |
| * extend by plugging in a different component (e.g. term frequency normalizer). |
| * <p> |
| * Finally, you can extend the low level {@link org.apache.lucene.search.similarities.Similarity Similarity} directly |
| * to implement a new retrieval model. |
| * <p> |
| * See the {@link org.apache.lucene.search.similarities} package documentation for information |
| * on the built-in available scoring models and extending or changing Similarity. |
| * |
| * <h3>Integrating field values into the score</h3> |
| * <p>While similarities help score a document relatively to a query, it is also common for documents to hold |
| * features that measure the quality of a match. Such features are best integrated into the score by indexing |
| * a {@link org.apache.lucene.document.FeatureField FeatureField} with the document at index-time, and then |
| * combining the similarity score and the feature score using a linear combination. For instance the below |
| * query matches the same documents as {@code originalQuery} and computes scores as |
| * {@code similarityScore + 0.7 * featureScore}: |
| * <pre class="prettyprint"> |
| * Query originalQuery = new BooleanQuery.Builder() |
| * .add(new TermQuery(new Term("body", "apache")), Occur.SHOULD) |
| * .add(new TermQuery(new Term("body", "lucene")), Occur.SHOULD) |
| * .build(); |
| * Query featureQuery = FeatureField.newSaturationQuery("features", "pagerank"); |
| * Query query = new BooleanQuery.Builder() |
| * .add(originalQuery, Occur.MUST) |
| * .add(new BoostQuery(featureQuery, 0.7f), Occur.SHOULD) |
| * .build(); |
| * </pre> |
| * |
| * <p>A less efficient yet more flexible way of modifying scores is to index scoring features into |
| * doc-value fields and then combine them with the similarity score using a |
| * <a href="{@docRoot}/../queries/org/apache/lucene/queries/function/FunctionScoreQuery.html">FunctionScoreQuery</a> |
| * from the <a href="{@docRoot}/../queries/overview-summary.html">queries module</a>. For instance |
| * the below example shows how to compute scores as {@code similarityScore * Math.log(popularity)} |
| * using the <a href="{@docRoot}/../expressions/overview-summary.html">expressions module</a> and |
| * assuming that values for the {@code popularity} field have been set in a |
| * {@link org.apache.lucene.document.NumericDocValuesField NumericDocValuesField} at index time: |
| * <pre class="prettyprint"> |
| * // compile an expression: |
| * Expression expr = JavascriptCompiler.compile("_score * ln(popularity)"); |
| * |
| * // SimpleBindings just maps variables to SortField instances |
| * SimpleBindings bindings = new SimpleBindings(); |
| * bindings.add(new SortField("_score", SortField.Type.SCORE)); |
| * bindings.add(new SortField("popularity", SortField.Type.INT)); |
| * |
| * // create a query that matches based on 'originalQuery' but |
| * // scores using expr |
| * Query query = new FunctionScoreQuery( |
| * originalQuery, |
| * expr.getDoubleValuesSource(bindings)); |
| * </pre> |
| * |
| * <a name="customQueriesExpert"></a> |
| * <h2>Custom Queries — Expert Level</h2> |
| * |
| * <p>Custom queries are an expert level task, so tread carefully and be prepared to share your code if |
| * you want help. |
| * |
| * <p>With the warning out of the way, it is possible to change a lot more than just the Similarity |
| * when it comes to matching and scoring in Lucene. Lucene's search is a complex mechanism that is grounded by |
| * <span>three main classes</span>: |
| * <ol> |
| * <li> |
| * {@link org.apache.lucene.search.Query Query} — The abstract object representation of the |
| * user's information need.</li> |
| * <li> |
| * {@link org.apache.lucene.search.Weight Weight} — A specialization of a Query for a given |
| * index. This typically associates a Query object with index statistics that are later used to |
| * compute document scores. |
| * <li> |
| * {@link org.apache.lucene.search.Scorer Scorer} — The core class of the scoring process: |
| * for a given segment, scorers return {@link org.apache.lucene.search.Scorer#iterator iterators} |
| * over matches and give a way to compute the {@link org.apache.lucene.search.Scorer#score score} |
| * of these matches.</li> |
| * <li> |
| * {@link org.apache.lucene.search.BulkScorer BulkScorer} — An abstract class that scores |
| * a range of documents. A default implementation simply iterates through the hits from |
| * {@link org.apache.lucene.search.Scorer Scorer}, but some queries such as |
| * {@link org.apache.lucene.search.BooleanQuery BooleanQuery} have more efficient |
| * implementations.</li> |
| * </ol> |
| * Details on each of these classes, and their children, can be found in the subsections below. |
| * <h3>The Query Class</h3> |
| * <p>In some sense, the |
| * {@link org.apache.lucene.search.Query Query} |
| * class is where it all begins. Without a Query, there would be |
| * nothing to score. Furthermore, the Query class is the catalyst for the other scoring classes as it |
| * is often responsible |
| * for creating them or coordinating the functionality between them. The |
| * {@link org.apache.lucene.search.Query Query} class has several methods that are important for |
| * derived classes: |
| * <ol> |
| * <li>{@link org.apache.lucene.search.Query#createWeight(IndexSearcher,ScoreMode,float) createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)} — A |
| * {@link org.apache.lucene.search.Weight Weight} is the internal representation of the |
| * Query, so each Query implementation must |
| * provide an implementation of Weight. See the subsection on <a |
| * href="#weightClass">The Weight Interface</a> below for details on implementing the Weight |
| * interface.</li> |
| * <li>{@link org.apache.lucene.search.Query#rewrite(org.apache.lucene.index.IndexReader) rewrite(IndexReader reader)} — Rewrites queries into primitive queries. Primitive queries are: |
| * {@link org.apache.lucene.search.TermQuery TermQuery}, |
| * {@link org.apache.lucene.search.BooleanQuery BooleanQuery}, <span |
| * >and other queries that implement {@link org.apache.lucene.search.Query#createWeight(IndexSearcher,ScoreMode,float) createWeight(IndexSearcher searcher,ScoreMode scoreMode, float boost)}</span></li> |
| * </ol> |
| * <a name="weightClass"></a> |
| * <h3>The Weight Interface</h3> |
| * <p>The |
| * {@link org.apache.lucene.search.Weight Weight} |
| * interface provides an internal representation of the Query so that it can be reused. Any |
| * {@link org.apache.lucene.search.IndexSearcher IndexSearcher} |
| * dependent state should be stored in the Weight implementation, |
| * not in the Query class. The interface defines four main methods: |
| * <ol> |
| * <li> |
| * {@link org.apache.lucene.search.Weight#scorer scorer()} — |
| * Construct a new {@link org.apache.lucene.search.Scorer Scorer} for this Weight. See <a href="#scorerClass">The Scorer Class</a> |
| * below for help defining a Scorer. As the name implies, the Scorer is responsible for doing the actual scoring of documents |
| * given the Query. |
| * </li> |
| * <li> |
| * {@link org.apache.lucene.search.Weight#explain(org.apache.lucene.index.LeafReaderContext, int) |
| * explain(LeafReaderContext context, int doc)} — Provide a means for explaining why a given document was |
| * scored the way it was. |
| * Typically a weight such as TermWeight |
| * that scores via a {@link org.apache.lucene.search.similarities.Similarity Similarity} will make use of the Similarity's implementation: |
| * {@link org.apache.lucene.search.similarities.Similarity.SimScorer#explain(Explanation, long) SimScorer#explain(Explanation freq, long norm)}. |
| * </li> |
| * <li> |
| * {@link org.apache.lucene.search.Weight#extractTerms(java.util.Set) extractTerms(Set<Term> terms)} — Extract terms that |
| * this query operates on. This is typically used to support distributed search: knowing the terms that a query operates on helps |
| * merge index statistics of these terms so that scores are computed over a subset of the data like they would if all documents |
| * were in the same index. |
| * </li> |
| * <li> |
| * {@link org.apache.lucene.search.Weight#matches matches(LeafReaderContext context, int doc)} — Give information about positions |
| * and offsets of matches. This is typically useful to implement highlighting. |
| * </li> |
| * </ol> |
| * <a name="scorerClass"></a> |
| * <h3>The Scorer Class</h3> |
| * <p>The |
| * {@link org.apache.lucene.search.Scorer Scorer} |
| * abstract class provides common scoring functionality for all Scorer implementations and |
| * is the heart of the Lucene scoring process. The Scorer defines the following methods which |
| * must be implemented: |
| * <ol> |
| * <li> |
| * {@link org.apache.lucene.search.Scorer#iterator iterator()} — Return a |
| * {@link org.apache.lucene.search.DocIdSetIterator DocIdSetIterator} that can iterate over all |
| * document that matches this Query. |
| * </li> |
| * <li> |
| * {@link org.apache.lucene.search.Scorer#docID docID()} — Returns the id of the |
| * {@link org.apache.lucene.document.Document Document} that contains the match. |
| * </li> |
| * <li> |
| * {@link org.apache.lucene.search.Scorer#score score()} — Return the score of the |
| * current document. This value can be determined in any appropriate way for an application. For instance, the |
| * {@link org.apache.lucene.search.TermScorer TermScorer} simply defers to the configured Similarity: |
| * {@link org.apache.lucene.search.similarities.Similarity.SimScorer#score(float, long) SimScorer.score(float freq, long norm)}. |
| * </li> |
| * <li> |
| * {@link org.apache.lucene.search.Scorer#getChildren getChildren()} — Returns any child subscorers |
| * underneath this scorer. This allows for users to navigate the scorer hierarchy and receive more fine-grained |
| * details on the scoring process. |
| * </li> |
| * </ol> |
| * <a name="bulkScorerClass"></a> |
| * <h3>The BulkScorer Class</h3> |
| * <p>The |
| * {@link org.apache.lucene.search.BulkScorer BulkScorer} scores a range of documents. There is only one |
| * abstract method: |
| * <ol> |
| * <li> |
| * {@link org.apache.lucene.search.BulkScorer#score(org.apache.lucene.search.LeafCollector,org.apache.lucene.util.Bits,int,int) score(LeafCollector,Bits,int,int)} — |
| * Score all documents up to but not including the specified max document. |
| * </li> |
| * </ol> |
| * <h3>Why would I want to add my own Query?</h3> |
| * |
| * <p>In a nutshell, you want to add your own custom Query implementation when you think that Lucene's |
| * aren't appropriate for the |
| * task that you want to do. You might be doing some cutting edge research or you need more information |
| * back |
| * out of Lucene (similar to Doug adding SpanQuery functionality). |
| * |
| * <!-- TODO: integrate this better, it's better served as an intro than an appendix --> |
| * |
| * |
| * <a name="algorithm"></a> |
| * <h2>Appendix: Search Algorithm</h2> |
| * <p>This section is mostly notes on stepping through the Scoring process and serves as |
| * fertilizer for the earlier sections. |
| * <p>In the typical search application, a {@link org.apache.lucene.search.Query Query} |
| * is passed to the {@link org.apache.lucene.search.IndexSearcher IndexSearcher}, |
| * beginning the scoring process. |
| * <p>Once inside the IndexSearcher, a {@link org.apache.lucene.search.Collector Collector} |
| * is used for the scoring and sorting of the search results. |
| * These important objects are involved in a search: |
| * <ol> |
| * <li>The {@link org.apache.lucene.search.Weight Weight} object of the Query. The |
| * Weight object is an internal representation of the Query that allows the Query |
| * to be reused by the IndexSearcher.</li> |
| * <li>The IndexSearcher that initiated the call.</li> |
| * <li>A {@link org.apache.lucene.search.Sort Sort} object for specifying how to sort |
| * the results if the standard score-based sort method is not desired.</li> |
| * </ol> |
| * <p>Assuming we are not sorting (since sorting doesn't affect the raw Lucene score), |
| * we call one of the search methods of the IndexSearcher, passing in the |
| * {@link org.apache.lucene.search.Weight Weight} object created by |
| * {@link org.apache.lucene.search.IndexSearcher#createWeight(org.apache.lucene.search.Query,ScoreMode,float) |
| * IndexSearcher.createWeight(Query,ScoreMode,float)} and the number of results we want. |
| * This method returns a {@link org.apache.lucene.search.TopDocs TopDocs} object, |
| * which is an internal collection of search results. The IndexSearcher creates |
| * a {@link org.apache.lucene.search.TopScoreDocCollector TopScoreDocCollector} and |
| * passes it along with the Weight to another expert search method (for |
| * more on the {@link org.apache.lucene.search.Collector Collector} mechanism, |
| * see {@link org.apache.lucene.search.IndexSearcher IndexSearcher}). The TopScoreDocCollector |
| * uses a {@link org.apache.lucene.util.PriorityQueue PriorityQueue} to collect the |
| * top results for the search. |
| * <p>At last, we are actually going to score some documents. The score method takes in the Collector |
| * (most likely the TopScoreDocCollector or TopFieldCollector) and does its business. Of course, here |
| * is where things get involved. The {@link org.apache.lucene.search.Scorer Scorer} that is returned |
| * by the {@link org.apache.lucene.search.Weight Weight} object depends on what type of Query was |
| * submitted. In most real world applications with multiple query terms, the |
| * {@link org.apache.lucene.search.Scorer Scorer} is going to be a <code>BooleanScorer2</code> created |
| * from {@link org.apache.lucene.search.BooleanWeight BooleanWeight} (see the section on |
| * <a href="#customQueriesExpert">custom queries</a> for info on changing this). |
| * <p>Assuming a BooleanScorer2, we get a internal Scorer based on the required, optional and prohibited parts of the query. |
| * Using this internal Scorer, the BooleanScorer2 then proceeds into a while loop based on the |
| * {@link org.apache.lucene.search.DocIdSetIterator#nextDoc DocIdSetIterator.nextDoc()} method. The nextDoc() method advances |
| * to the next document matching the query. This is an abstract method in the Scorer class and is thus |
| * overridden by all derived implementations. If you have a simple OR query your internal Scorer is most |
| * likely a DisjunctionSumScorer, which essentially combines the scorers from the sub scorers of the OR'd terms. |
| */ |
| package org.apache.lucene.search; |
