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

Mostra 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_oe property

protected bool disableCoord
return	bool

highFreqBoost protected_oe property

protected float highFreqBoost
return	float

highFreqOccur protected_oe property

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

lowFreqBoost protected_oe property

protected float lowFreqBoost
return	float

lowFreqOccur protected_oe property

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

maxTermFrequency protected_oe property

protected float maxTermFrequency
return	float

terms protected_oe property

protected IList terms
return	IList