C# Class Lucene.Net.Queries.CommonTermsQuery

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 #add(Term) 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 Similarity#coord(int,int) 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.

Inheritance: Lucene.Net.Search.Query

Show file Open project: paulirwin/lucene.net

Protected Properties

Property	Type	Description
disableCoord	bool
highFreqBoost	float
highFreqOccur	Lucene.Net.Search.BooleanClause.Occur
lowFreqBoost	float
lowFreqOccur	Lucene.Net.Search.BooleanClause.Occur
maxTermFrequency	float
terms	IList

Public Methods

Method	Description
Add ( Lucene.Net.Index.Term term ) : void	Adds a term to the CommonTermsQuery
CollectTermContext ( IndexReader reader, IList leaves, TermContext contextArray, Lucene.Net.Index.Term queryTerms ) : void
CommonTermsQuery ( BooleanClause highFreqOccur, BooleanClause lowFreqOccur, float maxTermFrequency ) : System	Creates a new CommonTermsQuery
CommonTermsQuery ( BooleanClause highFreqOccur, BooleanClause lowFreqOccur, float maxTermFrequency, bool disableCoord ) : System	Creates a new CommonTermsQuery
Equals ( object obj ) : bool
ExtractTerms ( ISet terms ) : void
GetHashCode ( ) : int
Rewrite ( IndexReader reader ) : Query
ToString ( string field ) : string

Protected Methods

Method	Description
BuildQuery ( int maxDoc, TermContext contextArray, Lucene.Net.Index.Term queryTerms ) : Query
CalcHighFreqMinimumNumberShouldMatch ( int numOptional ) : int
CalcLowFreqMinimumNumberShouldMatch ( int numOptional ) : int
NewTermQuery ( Lucene.Net.Index.Term term, TermContext context ) : Query	Builds a new TermQuery instance. This is intended for subclasses that wish to customize the generated queries.

Private Methods

Method	Description
MinNrShouldMatch ( float minNrShouldMatch, int numOptional ) : int

Method Details

Add() public method

Adds a term to the CommonTermsQuery

public Add ( Lucene.Net.Index.Term term ) : void
term	Lucene.Net.Index.Term	/// the term to add
return	void

BuildQuery() protected method

protected BuildQuery ( int maxDoc, TermContext contextArray, Lucene.Net.Index.Term queryTerms ) : Query
maxDoc	int
contextArray	Lucene.Net.Index.TermContext
queryTerms	Lucene.Net.Index.Term
return	Lucene.Net.Search.Query

CalcHighFreqMinimumNumberShouldMatch() protected method

protected CalcHighFreqMinimumNumberShouldMatch ( int numOptional ) : int
numOptional	int
return	int

CalcLowFreqMinimumNumberShouldMatch() protected method

protected CalcLowFreqMinimumNumberShouldMatch ( int numOptional ) : int
numOptional	int
return	int

CollectTermContext() public method

public CollectTermContext ( IndexReader reader, IList leaves, TermContext contextArray, Lucene.Net.Index.Term queryTerms ) : void
reader	Lucene.Net.Index.IndexReader
leaves	IList
contextArray	Lucene.Net.Index.TermContext
queryTerms	Lucene.Net.Index.Term
return	void

CommonTermsQuery() public method

Creates a new CommonTermsQuery

/// if is pass as lowFreqOccur or /// highFreqOccur

public CommonTermsQuery ( BooleanClause highFreqOccur, BooleanClause lowFreqOccur, float maxTermFrequency ) : System
highFreqOccur	Lucene.Net.Search.BooleanClause	/// used for high frequency terms
lowFreqOccur	Lucene.Net.Search.BooleanClause	/// used for low frequency terms
maxTermFrequency	float	/// 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.
return	System

CommonTermsQuery() public method

Creates a new CommonTermsQuery

/// if is pass as lowFreqOccur or /// highFreqOccur

public CommonTermsQuery ( BooleanClause highFreqOccur, BooleanClause lowFreqOccur, float maxTermFrequency, bool disableCoord ) : System
highFreqOccur	Lucene.Net.Search.BooleanClause	/// used for high frequency terms
lowFreqOccur	Lucene.Net.Search.BooleanClause	/// used for low frequency terms
maxTermFrequency	float	/// 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	bool	/// disables in scoring for the low /// / high frequency sub-queries
return	System

Equals() public method

public Equals ( object obj ) : bool
obj	object
return	bool

ExtractTerms() public method

public ExtractTerms ( ISet terms ) : void
terms	ISet
return	void

GetHashCode() public method

public GetHashCode ( ) : int
return	int

NewTermQuery() protected method

Builds a new TermQuery instance.

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

protected NewTermQuery ( Lucene.Net.Index.Term term, TermContext context ) : Query
term	Lucene.Net.Index.Term	term
context	Lucene.Net.Index.TermContext	the TermContext to be used to create the low level term query. Can be `null`.
return	Lucene.Net.Search.Query

Rewrite() public method

public Rewrite ( IndexReader reader ) : Query
reader	Lucene.Net.Index.IndexReader
return	Lucene.Net.Search.Query

ToString() public method

public ToString ( string field ) : string
field	string
return	string

Property Details

disableCoord protected property

protected bool disableCoord
return	bool

highFreqBoost protected property

protected float highFreqBoost
return	float

highFreqOccur protected property

protected BooleanClause.Occur,Lucene.Net.Search highFreqOccur
return	Lucene.Net.Search.BooleanClause.Occur

lowFreqBoost protected property

protected float lowFreqBoost
return	float

lowFreqOccur protected property

protected BooleanClause.Occur,Lucene.Net.Search lowFreqOccur
return	Lucene.Net.Search.BooleanClause.Occur

maxTermFrequency protected property

protected float maxTermFrequency
return	float

terms protected property

protected IList terms
return	IList