org.apache.lucene.search

Class DisjunctionMaxQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.search.DisjunctionMaxQuery

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable

public class DisjunctionMaxQuery
extends 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

Constructor Summary

Constructors

Constructor and Description
DisjunctionMaxQuery(java.util.Collection disjuncts, float tieBreakerMultiplier) Creates a new DisjunctionMaxQuery
DisjunctionMaxQuery(float tieBreakerMultiplier) Creates a new empty DisjunctionMaxQuery.

Method Summary

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

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 - this 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(java.util.Collection 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(java.util.Collection disjuncts)

Add a collection of disjuncts to this disjunction via Iterable

iterator

public java.util.Iterator iterator()

An Iterator over the disjuncts

rewrite

public Query rewrite(IndexReader reader)
              throws java.io.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:

java.io.IOException

clone

public java.lang.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(java.util.Set terms)

Description copied from class: Query

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

Overrides:

extractTerms in class Query

toString

public java.lang.String toString(java.lang.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(java.lang.Object o)

Return true iff we represent the same query as o

Overrides:

equals in class java.lang.Object

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 java.lang.Object

Returns:

the hash code