Package org.apache.lucene.sandbox.queries

Class FuzzyLikeThisQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.sandbox.queries.FuzzyLikeThisQuery

public class FuzzyLikeThisQuery
extends Query

Fuzzifies ALL terms provided as strings and then picks the best n differentiating terms. In effect this mixes the behaviour of FuzzyQuery and MoreLikeThis but with special consideration of fuzzy scoring factors. This generally produces good results for queries where users may provide details in a number of fields and have no knowledge of boolean query syntax and also want a degree of fuzzy matching and a fast query. For each source term the fuzzy variants are held in a BooleanQuery with no coord factor (because we are not looking for matches on multiple variants in any one doc). Additionally, a specialized TermQuery is used for variants and does not use that variant term's IDF because this would favour rarer terms eg misspellings. Instead, all variants use the same IDF ranking (the one for the source query term) and this is factored into the variant's boost. If the source query term does not exist in the index the average IDF of the variants is used.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
(package private) static class	FuzzyLikeThisQuery.FieldVals
private static class	FuzzyLikeThisQuery.ScoreTerm
private static class	FuzzyLikeThisQuery.ScoreTermQueue

Field Summary

Fields

Modifier and Type	Field	Description
(package private) Analyzer	analyzer
(package private) ArrayList<FuzzyLikeThisQuery.FieldVals>	fieldVals
(package private) boolean	ignoreTF
(package private) int	MAX_VARIANTS_PER_TERM
private int	maxNumTerms
(package private) static TFIDFSimilarity	sim

Constructor Summary

Constructors

Constructor	Description
FuzzyLikeThisQuery(int maxNumTerms, Analyzer analyzer)

Method Summary

Modifier and Type	Method	Description
void	addTerms(String queryString, String fieldName, float minSimilarity, int prefixLength)	Adds user input for "fuzzification"
private void	addTerms(IndexReader reader, FuzzyLikeThisQuery.FieldVals f, FuzzyLikeThisQuery.ScoreTermQueue q)
boolean	equals(Object other)	Override and implement query instance equivalence properly in a subclass.
private boolean	equalsTo(FuzzyLikeThisQuery other)
int	hashCode()	Override and implement query hash code properly in a subclass.
boolean	isIgnoreTF()
private Query	newTermQuery(IndexReader reader, Term term)
Query	rewrite(IndexReader reader)	Expert: called to re-write queries into primitive queries.
void	setIgnoreTF(boolean ignoreTF)
String	toString(String field)	Prints a query to a string, with field assumed to be the default field and omitted.
void	visit(QueryVisitor visitor)	Recurse through the query tree, visiting any child queries

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

classHash, createWeight, sameClassAs, toString

Methods inherited from class java.lang.Object

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

Field Details

sim

static TFIDFSimilarity sim

fieldVals

ArrayList<FuzzyLikeThisQuery.FieldVals> fieldVals

analyzer

Analyzer analyzer

MAX_VARIANTS_PER_TERM

int MAX_VARIANTS_PER_TERM

ignoreTF

boolean ignoreTF

maxNumTerms

private int maxNumTerms

Constructor Details

FuzzyLikeThisQuery

public FuzzyLikeThisQuery(int maxNumTerms,
 Analyzer analyzer)

Parameters:

maxNumTerms - The total number of terms clauses that will appear once rewritten as a BooleanQuery

Method Details

hashCode

public int hashCode()

Description copied from class: Query

Override and implement query hash code properly in a subclass. This is required so that QueryCache works properly.

Specified by:

hashCode in class Query

See Also:

• Query.equals(Object)

equals

public boolean equals(Object other)

Description copied from class: Query

Override and implement query instance equivalence properly in a subclass. This is required so that QueryCache works properly. Typically a query will be equal to another only if it's an instance of the same class and its document-filtering properties are identical that other instance. Utility methods are provided for certain repetitive code.

Specified by:

equals in class Query

See Also:

• Query.sameClassAs(Object)
• Query.classHash()

equalsTo

private boolean equalsTo(FuzzyLikeThisQuery other)

addTerms

public void addTerms(String queryString,
 String fieldName,
 float minSimilarity,
 int prefixLength)

Adds user input for "fuzzification"

Parameters:

queryString - The string which will be parsed by the analyzer and for which fuzzy variants will be parsed

minSimilarity - The minimum similarity of the term variants; must be 0, 1 or 2 (see FuzzyTermsEnum)

prefixLength - Length of required common prefix on variant terms (see FuzzyTermsEnum)

addTerms

private void addTerms(IndexReader reader,
 FuzzyLikeThisQuery.FieldVals f,
 FuzzyLikeThisQuery.ScoreTermQueue q)
               throws IOException

Throws:

IOException

newTermQuery

private Query newTermQuery(IndexReader reader,
 Term term)
                    throws IOException

Throws:

IOException

visit

public void visit(QueryVisitor visitor)

Description copied from class: Query

Recurse through the query tree, visiting any child queries

Overrides:

visit in class Query

Parameters:

visitor - a QueryVisitor to be called by each query in the tree

rewrite

public Query rewrite(IndexReader reader)
              throws IOException

Description copied from class: Query

Expert: called to re-write queries into primitive queries. For example, a PrefixQuery will be rewritten into a BooleanQuery that consists of TermQuerys.

Overrides:

rewrite in class Query

Throws:

IOException

toString

public String toString(String field)

Description copied from class: Query

Prints a query to a string, with field assumed to be the default field and omitted.

Specified by:

toString in class Query

isIgnoreTF

public boolean isIgnoreTF()

setIgnoreTF

public void setIgnoreTF(boolean ignoreTF)