org.apache.lucene.queries

Class CommonTermsQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.queries.CommonTermsQuery

All Implemented Interfaces:

Cloneable

public class CommonTermsQuery
extends Query

A query that executes high-frequency terms in a optional sub-query to prevent slow queries due to "common" terms like stopwords. This query builds 2 queries off the added terms: low-frequency terms are added to a required boolean clause and high-frequency terms are added to an optional boolean clause. The optional clause is only executed if the required "low-frequency" clause matches. Scores produced by this query will be slightly different than plain BooleanQuery scorer mainly due to differences in the number of leaf queries in the required boolean clause. In most cases, high-frequency terms are unlikely to significantly contribute to the document score unless at least one of the low-frequency terms are matched. This query can improve query execution times significantly if applicable.

CommonTermsQuery has several advantages over stopword filtering at index or query time since a term can be "classified" based on the actual document frequency in the index and can prevent slow queries even across domains without specialized stopword files.

Note: if the query only contains high-frequency terms the query is rewritten into a plain conjunction query ie. all high-frequency terms need to match in order to match a document.

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	disableCoord
protected float	highFreqBoost
protected float	highFreqMinNrShouldMatch
protected BooleanClause.Occur	highFreqOccur
protected float	lowFreqBoost
protected float	lowFreqMinNrShouldMatch
protected BooleanClause.Occur	lowFreqOccur
protected float	maxTermFrequency
protected List<Term>	terms

Constructor Summary

Constructors

Constructor and Description
CommonTermsQuery(BooleanClause.Occur highFreqOccur, BooleanClause.Occur lowFreqOccur, float maxTermFrequency) Creates a new CommonTermsQuery
CommonTermsQuery(BooleanClause.Occur highFreqOccur, BooleanClause.Occur lowFreqOccur, float maxTermFrequency, boolean disableCoord) Creates a new CommonTermsQuery

Method Summary

Methods

Modifier and Type	Method and Description
void	add(Term term) Adds a term to the CommonTermsQuery
protected Query	buildQuery(int maxDoc, TermContext[] contextArray, Term[] queryTerms)
protected int	calcHighFreqMinimumNumberShouldMatch(int numOptional)
protected int	calcLowFreqMinimumNumberShouldMatch(int numOptional)
void	collectTermContext(IndexReader reader, List<AtomicReaderContext> leaves, TermContext[] contextArray, Term[] queryTerms)
boolean	equals(Object obj)
void	extractTerms(Set<Term> terms)
float	getHighFreqMinimumNumberShouldMatch() Gets the minimum number of the optional high frequent BooleanClauses which must be satisfied.
float	getLowFreqMinimumNumberShouldMatch() Gets the minimum number of the optional low frequent BooleanClauses which must be satisfied.
int	hashCode()
boolean	isCoordDisabled() Returns true iff Similarity.coord(int,int) is disabled in scoring for the high and low frequency query instance.
protected Query	newTermQuery(Term term, TermContext context) Builds a new TermQuery instance.
Query	rewrite(IndexReader reader)
void	setHighFreqMinimumNumberShouldMatch(float min) Specifies a minimum number of the high frequent optional BooleanClauses which must be satisfied in order to produce a match on the low frequency terms query part.
void	setLowFreqMinimumNumberShouldMatch(float min) Specifies a minimum number of the low frequent optional BooleanClauses which must be satisfied in order to produce a match on the low frequency terms query part.
String	toString(String field)

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

clone, createWeight, getBoost, setBoost, toString

Methods inherited from class java.lang.Object

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

Field Detail

terms

protected final List<Term> terms

disableCoord

protected final boolean disableCoord

maxTermFrequency

protected final float maxTermFrequency

lowFreqOccur

protected final BooleanClause.Occur lowFreqOccur

highFreqOccur

protected final BooleanClause.Occur highFreqOccur

lowFreqBoost

protected float lowFreqBoost

highFreqBoost

protected float highFreqBoost

lowFreqMinNrShouldMatch

protected float lowFreqMinNrShouldMatch

highFreqMinNrShouldMatch

protected float highFreqMinNrShouldMatch

Constructor Detail

CommonTermsQuery

public CommonTermsQuery(BooleanClause.Occur highFreqOccur,
                BooleanClause.Occur lowFreqOccur,
                float maxTermFrequency)

Creates a new CommonTermsQuery

Parameters:

highFreqOccur - BooleanClause.Occur used for high frequency terms

lowFreqOccur - BooleanClause.Occur used for low frequency terms

maxTermFrequency - a value in [0..1) (or absolute number >=1) representing the maximum threshold of a terms document frequency to be considered a low frequency term.

Throws:

IllegalArgumentException - if BooleanClause.Occur.MUST_NOT is pass as lowFreqOccur or highFreqOccur

CommonTermsQuery

public CommonTermsQuery(BooleanClause.Occur highFreqOccur,
                BooleanClause.Occur lowFreqOccur,
                float maxTermFrequency,
                boolean disableCoord)

Creates a new CommonTermsQuery

Parameters:

highFreqOccur - BooleanClause.Occur used for high frequency terms

lowFreqOccur - BooleanClause.Occur used for low frequency terms

maxTermFrequency - a value in [0..1) (or absolute number >=1) representing the maximum threshold of a terms document frequency to be considered a low frequency term.

disableCoord - disables Similarity.coord(int,int) in scoring for the low / high frequency sub-queries

Throws:

IllegalArgumentException - if BooleanClause.Occur.MUST_NOT is pass as lowFreqOccur or highFreqOccur

Method Detail

add

public void add(Term term)

Adds a term to the CommonTermsQuery

Parameters:

term - the term to add

rewrite

public Query rewrite(IndexReader reader)
              throws IOException

Overrides:

rewrite in class Query

Throws:

IOException

calcLowFreqMinimumNumberShouldMatch

protected int calcLowFreqMinimumNumberShouldMatch(int numOptional)

calcHighFreqMinimumNumberShouldMatch

protected int calcHighFreqMinimumNumberShouldMatch(int numOptional)

buildQuery

protected Query buildQuery(int maxDoc,
               TermContext[] contextArray,
               Term[] queryTerms)

collectTermContext

public void collectTermContext(IndexReader reader,
                      List<AtomicReaderContext> leaves,
                      TermContext[] contextArray,
                      Term[] queryTerms)
                        throws IOException

Throws:

IOException

isCoordDisabled

public boolean isCoordDisabled()

Returns true iff Similarity.coord(int,int) is disabled in scoring for the high and low frequency query instance. The top level query will always disable coords.

setLowFreqMinimumNumberShouldMatch

public void setLowFreqMinimumNumberShouldMatch(float min)

Specifies a minimum number of the low frequent optional BooleanClauses which must be satisfied in order to produce a match on the low frequency terms query part. This method accepts a float value in the range [0..1) as a fraction of the actual query terms in the low frequent clause or a number >=1 as an absolut number of clauses that need to match.

By default no optional clauses are necessary for a match (unless there are no required clauses). If this method is used, then the specified number of clauses is required.

Parameters:

min - the number of optional clauses that must match

getLowFreqMinimumNumberShouldMatch

public float getLowFreqMinimumNumberShouldMatch()

Gets the minimum number of the optional low frequent BooleanClauses which must be satisfied.

setHighFreqMinimumNumberShouldMatch

public void setHighFreqMinimumNumberShouldMatch(float min)

Specifies a minimum number of the high frequent optional BooleanClauses which must be satisfied in order to produce a match on the low frequency terms query part. This method accepts a float value in the range [0..1) as a fraction of the actual query terms in the low frequent clause or a number >=1 as an absolut number of clauses that need to match.

By default no optional clauses are necessary for a match (unless there are no required clauses). If this method is used, then the specified number of clauses is required.

Parameters:

min - the number of optional clauses that must match

getHighFreqMinimumNumberShouldMatch

public float getHighFreqMinimumNumberShouldMatch()

Gets the minimum number of the optional high frequent BooleanClauses which must be satisfied.

extractTerms

public void extractTerms(Set<Term> terms)

Overrides:

extractTerms in class Query

toString

public String toString(String field)

Specified by:

toString in class Query

hashCode

public int hashCode()

Overrides:

hashCode in class Query

equals

public boolean equals(Object obj)

Overrides:

equals in class Query

newTermQuery

protected Query newTermQuery(Term term,
                 TermContext context)

Builds a new TermQuery instance.

This is intended for subclasses that wish to customize the generated queries.

Parameters:

term - term

context - the TermContext to be used to create the low level term query. Can be null.

Returns:

new TermQuery instance