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.
Nested Class Summary
Nested Classes Modifier and Type Class Description
DisjunctionMaxQuery.DisjunctionMaxWeightExpert: the Weight for DisjunctionMaxQuery, used to normalize, score and explain these queries.
All Methods Instance Methods Concrete Methods Modifier and Type Method Description
createWeight(IndexSearcher searcher, boolean needsScores, float boost)Create the Weight used to score us
equals(Object other)Return true iff we represent the same query as o
hashCode()Compute a hash code for hashing us
rewrite(IndexReader reader)Optimize our representation and our subqueries representations
toString(String field)Prettyprint us.
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
public DisjunctionMaxQuery(Collection<Query> disjuncts, float tieBreakerMultiplier)Creates a new DisjunctionMaxQuery
Collection<Query>of all the disjuncts to add
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.
public float getTieBreakerMultiplier()
- tie breaker value for multiple matches.
public Weight createWeight(IndexSearcher searcher, boolean needsScores, float boost) throws IOExceptionCreate the Weight used to score us
public Query rewrite(IndexReader reader) throws IOExceptionOptimize our representation and our subqueries representations
public boolean equals(Object other)Return true iff we represent the same query as o