org.apache.lucene.search
Class DisjunctionMaxQuery
- Cloneable, Serializable
public class DisjunctionMaxQuery
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.
DisjunctionMaxQuery(Collection disjuncts, float tieBreakerMultiplier) - Creates a new DisjunctionMaxQuery
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DisjunctionMaxQuery(float tieBreakerMultiplier) - Creates a new empty DisjunctionMaxQuery.
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void | add(Collection disjuncts) - Add a collection of disjuncts to this disjunction
via Iterable
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void | add(Query query) - Add a subquery to this disjunction
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Object | clone() - Create a shallow copy of us -- used in rewriting if necessary
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protected Weight | createWeight(Searcher searcher) - Expert: Constructs an appropriate Weight implementation for this query.
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boolean | equals(Object o) - Return true iff we represent the same query as o
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void | extractTerms(Set terms) - Expert: adds all terms occuring in this query to the terms set.
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int | hashCode() - Compute a hash code for hashing us
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Iterator | iterator() - An Iterator over the disjuncts
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Query | rewrite(IndexReader reader) - Optimize our representation and our subqueries representations
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String | toString(String field) - Prettyprint us.
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clone , combine , createWeight , extractTerms , getBoost , getSimilarity , mergeBooleanQueries , rewrite , setBoost , toString , toString , weight |
DisjunctionMaxQuery
public DisjunctionMaxQuery(Collection disjuncts,
float tieBreakerMultiplier)
Creates a new DisjunctionMaxQuery
disjuncts
- a Collection of all the disjuncts to addtieBreakerMultiplier
- the weight to give to each matching non-maximum disjunct
DisjunctionMaxQuery
public DisjunctionMaxQuery(float tieBreakerMultiplier)
Creates a new empty DisjunctionMaxQuery. Use add() to add the subqueries.
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.
add
public void add(Collection disjuncts)
Add a collection of disjuncts to this disjunction
via Iterable
add
public void add(Query query)
Add a subquery to this disjunction
query
- the disjunct added
clone
public Object clone()
Create a shallow copy of us -- used in rewriting if necessary
- clone in interface Query
- a copy of us (but reuse, don't copy, our subqueries)
createWeight
protected Weight createWeight(Searcher searcher)
throws IOException
Expert: Constructs an appropriate Weight implementation for this query.
Only implemented by primitive queries, which re-write to themselves.
- createWeight in interface Query
equals
public boolean equals(Object o)
Return true iff we represent the same query as o
- true iff o is a DisjunctionMaxQuery with the same boost and the same subqueries, in the same order, as us
extractTerms
public void extractTerms(Set terms)
Expert: adds all terms occuring in this query to the terms set. Only
works if this query is in its
rewritten
form.
- extractTerms in interface Query
hashCode
public int hashCode()
Compute a hash code for hashing us
iterator
public Iterator iterator()
An Iterator over the disjuncts
rewrite
public Query rewrite(IndexReader reader)
throws IOException
Optimize our representation and our subqueries representations
- rewrite in interface Query
reader
- the IndexReader we query
- 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.
- toString in interface Query
field
- the field to which we are applied
- a string that shows what we do, of the form "(disjunct1 | disjunct2 | ... | disjunctn)^boost"
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