org.apache.lucene.search

Class DisjunctionMaxQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.search.DisjunctionMaxQuery

All Implemented Interfaces:

Serializable, Cloneable, Iterable<Query>

public class DisjunctionMaxQuery
extends Query
implements Iterable<Query>

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.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected class	DisjunctionMaxQuery.DisjunctionMaxWeight Expert: the Weight for DisjunctionMaxQuery, used to normalize, score and explain these queries.

Constructor Summary

Constructors

Constructor and Description
DisjunctionMaxQuery(Collection<Query> disjuncts, float tieBreakerMultiplier) Creates a new DisjunctionMaxQuery
DisjunctionMaxQuery(float tieBreakerMultiplier) Creates a new empty DisjunctionMaxQuery.

Method Summary

Methods

Modifier and Type	Method and Description
void	add(Collection<Query> disjuncts) Add a collection of disjuncts to this disjunction via Iterable
void	add(Query query) Add a subquery to this disjunction
Object	clone() Create a shallow copy of us -- used in rewriting if necessary
Weight	createWeight(Searcher searcher) Create the Weight used to score us
boolean	equals(Object o) Return true iff we represent the same query as o
void	extractTerms(Set<Term> terms) Expert: adds all terms occurring in this query to the terms set.
int	hashCode() Compute a hash code for hashing us
Iterator<Query>	iterator() An Iterator over the disjuncts
Query	rewrite(IndexReader reader) Optimize our representation and our subqueries representations
String	toString(String field) Prettyprint us.

Methods inherited from class org.apache.lucene.search.Query

combine, getBoost, getSimilarity, mergeBooleanQueries, setBoost, toString, weight

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

DisjunctionMaxQuery

public DisjunctionMaxQuery(float tieBreakerMultiplier)

Creates a new empty DisjunctionMaxQuery. Use add() to add the subqueries.

Parameters:

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.

DisjunctionMaxQuery

public DisjunctionMaxQuery(Collection<Query> disjuncts,
                   float tieBreakerMultiplier)

Creates a new DisjunctionMaxQuery

Parameters:

disjuncts - a Collection of all the disjuncts to add

tieBreakerMultiplier - the weight to give to each matching non-maximum disjunct

Method Detail

add

public void add(Query query)

Add a subquery to this disjunction

Parameters:

query - the disjunct added

add

public void add(Collection<Query> disjuncts)

Add a collection of disjuncts to this disjunction via Iterable

iterator

public Iterator<Query> iterator()

An Iterator over the disjuncts

Specified by:

iterator in interface Iterable<Query>

createWeight

public Weight createWeight(Searcher searcher)
                    throws IOException

Create the Weight used to score us

Overrides:

createWeight in class Query

Throws:

IOException

rewrite

public Query rewrite(IndexReader reader)
              throws IOException

Optimize our representation and our subqueries representations

Overrides:

rewrite in class Query

Parameters:

reader - the IndexReader we query

Returns:

an optimized copy of us (which may not be a copy if there is nothing to optimize)

Throws:

IOException

clone

public Object clone()

Create a shallow copy of us -- used in rewriting if necessary

Overrides:

clone in class Query

Returns:

a copy of us (but reuse, don't copy, our subqueries)

extractTerms

public void extractTerms(Set<Term> terms)

Description copied from class: Query

Expert: adds all terms occurring in this query to the terms set. Only works if this query is in its rewritten form.

Overrides:

extractTerms in class Query

toString

public String toString(String field)

Prettyprint us.

Specified by:

toString in class Query

Parameters:

field - the field to which we are applied

Returns:

a string that shows what we do, of the form "(disjunct1 | disjunct2 | ... | disjunctn)^boost"

equals

public boolean equals(Object o)

Return true iff we represent the same query as o

Overrides:

equals in class Query

Parameters:

o - another object

Returns:

true iff o is a DisjunctionMaxQuery with the same boost and the same subqueries, in the same order, as us

hashCode

public int hashCode()

Compute a hash code for hashing us

Overrides:

hashCode in class Query

Returns:

the hash code