org.apache.lucene.search

Class DisjunctionMaxQuery

public class DisjunctionMaxQuery extends Query

A query that generates the union of the documents produced by its subqueries, and that scores each document as the maximum score for that document produced by any subquery plus a tie breaking increment for any additional matching subqueries. This is useful to search 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.

Author: Chuck Williams

Constructor Summary
DisjunctionMaxQuery(float tieBreakerMultiplier)
Creates a new empty DisjunctionMaxQuery.
DisjunctionMaxQuery(Collection disjuncts, float tieBreakerMultiplier)
Creates a new DisjunctionMaxQuery
Method Summary
voidadd(Query query)
Add a subquery to this disjunction
voidadd(Collection disjuncts)
Add a collection of disjuncts to this disjunction via Iterable
Objectclone()
Create a shallow copy of us -- used in rewriting if necessary
protected WeightcreateWeight(Searcher searcher)
booleanequals(Object o)
Return true iff we represent the same query as o
inthashCode()
Compute a hash code for hashing us
Iteratoriterator()
An Iterator over the disjuncts
Queryrewrite(IndexReader reader)
Optimize our representation and our subqueries representations
StringtoString(String field)
Prettyprint us.

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(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(Collection disjuncts)
Add a collection of disjuncts to this disjunction via Iterable

clone

public Object clone()
Create a shallow copy of us -- used in rewriting if necessary

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

createWeight

protected Weight createWeight(Searcher searcher)

equals

public boolean equals(Object o)
Return true iff we represent the same query as o

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

Returns: the hash code

iterator

public Iterator iterator()
An Iterator over the disjuncts

rewrite

public Query rewrite(IndexReader reader)
Optimize our representation and our subqueries representations

Parameters: reader the IndexReader we query

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

toString

public String toString(String field)
Prettyprint us.

Parameters: field the field to which we are applied

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

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