API Documentation

Zend/Search/Lucene/Search/Similarity.php

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Zend Framework

LICENSE

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Category
Zend  
Copyright
Copyright (c) 2005-2012 Zend Technologies USA Inc. (http://www.zend.com)  
License
New BSD License  
Package
Zend_Search_Lucene  
Subpackage
Search  
Version
$Id: Similarity.php 24594 2012-01-05 21:27:01Z matthew $  

\Zend_Search_Lucene_Search_Similarity

Package: Zend\Search\Lucene\Search

Children
\Zend_Search_Lucene_Search_Similarity_Default
Category
Zend  
Copyright
Copyright (c) 2005-2012 Zend Technologies USA Inc. (http://www.zend.com)  
License
New BSD License  

Properties

Propertyprivate\Zend_Search_Lucene_Search_Similarity  $_defaultImpl= ''
static

The Similarity implementation used by default.

Propertyprivatearray  $_normTable= 'array( 0 => 0.0'
static

Cache of decoded bytes.

Array of floats

Default valuearray( 0 => 0.0Details
Type
array

Methods

methodprivate_floatToByte(  $f ) : float
static

Float to byte conversion

Parameters
Name Type Description
$f
Returns
Type Description
float
methodpubliccoord( integer $overlap, integer $maxOverlap ) : float
abstract

Computes a score factor based on the fraction of all query terms that a document contains. This value is multiplied into scores.

The presence of a large portion of the query terms indicates a better match with the query, so implemenations of this method usually return larger values when the ratio between these parameters is large and smaller values when the ratio between them is small.

overlap - the number of query terms matched in the document maxOverlap - the total number of terms in the query Returns a score factor based on term overlap with the query

Parameters
Name Type Description
$overlap integer
$maxOverlap integer
Returns
Type Description
float
methodpublicdecodeNorm( integer $byte ) : float
static

Decodes a normalization factor stored in an index.

Parameters
Name Type Description
$byte integer
Returns
Type Description
float
methodpublicencodeNorm( float $f ) : integer
static

Encodes a normalization factor for storage in an index.

The encoding uses a five-bit exponent and three-bit mantissa, thus representing values from around 7x10^9 to 2x10^-9 with about one significant decimal digit of accuracy. Zero is also represented. Negative numbers are rounded up to zero. Values too large to represent are rounded down to the largest representable value. Positive values too small to represent are rounded up to the smallest positive representable value.

Parameters
Name Type Description
$f float
Returns
Type Description
integer
methodpublicgetDefault( ) : \Zend_Search_Lucene_Search_Similarity
static

Return the default Similarity implementation used by indexing and search code.

Returns
Type Description
\Zend_Search_Lucene_Search_Similarity
methodpublicidf( mixed $input, \Zend_Search_Lucene_Interface $reader ) : \a

Computes a score factor for a simple term or a phrase.

The default implementation is: return idfFreq(searcher.docFreq(term), searcher.maxDoc());

input - the term in question or array of terms reader - reader the document collection being searched Returns a score factor for the term

Parameters
Name Type Description
$input mixed
$reader \Zend_Search_Lucene_Interface
Returns
Type Description
\a score factor for the term
methodpublicidfFreq( integer $docFreq, integer $numDocs ) : float
abstract

Computes a score factor based on a term's document frequency (the number of documents which contain the term). This value is multiplied by the tf(int) factor for each term in the query and these products are then summed to form the initial score for a document.

Terms that occur in fewer documents are better indicators of topic, so implemenations of this method usually return larger values for rare terms, and smaller values for common terms.

docFreq - the number of documents which contain the term numDocs - the total number of documents in the collection Returns a score factor based on the term's document frequency

Parameters
Name Type Description
$docFreq integer
$numDocs integer
Returns
Type Description
float
methodpubliclengthNorm( string $fieldName, integer $numTokens ) : float
abstract

Computes the normalization value for a field given the total number of terms contained in a field. These values, together with field boosts, are stored in an index and multipled into scores for hits on each field by the search code.

Matches in longer fields are less precise, so implemenations of this method usually return smaller values when 'numTokens' is large, and larger values when 'numTokens' is small.

That these values are computed under IndexWriter::addDocument(Document) and stored then using encodeNorm(float). Thus they have limited precision, and documents must be re-indexed if this method is altered.

fieldName - name of field numTokens - the total number of tokens contained in fields named 'fieldName' of 'doc'. Returns a normalization factor for hits on this field of this document

Parameters
Name Type Description
$fieldName string
$numTokens integer
Returns
Type Description
float
methodpublicqueryNorm( float $sumOfSquaredWeights ) : float
abstract

Computes the normalization value for a query given the sum of the squared weights of each of the query terms. This value is then multipled into the weight of each query term.

This does not affect ranking, but rather just attempts to make scores from different queries comparable.

sumOfSquaredWeights - the sum of the squares of query term weights Returns a normalization factor for query weights

Parameters
Name Type Description
$sumOfSquaredWeights float
Returns
Type Description
float
methodpublicsetDefault( \Zend_Search_Lucene_Search_Similarity $similarity ) : void
static

Set the default Similarity implementation used by indexing and search code.

Parameters
Name Type Description
$similarity \Zend_Search_Lucene_Search_Similarity
methodpublicsloppyFreq( integer $distance ) : float
abstract

Computes the amount of a sloppy phrase match, based on an edit distance.

This value is summed for each sloppy phrase match in a document to form the frequency that is passed to tf(float).

A phrase match with a small edit distance to a document passage more closely matches the document, so implementations of this method usually return larger values when the edit distance is small and smaller values when it is large.

distance - the edit distance of this sloppy phrase match Returns the frequency increment for this match

Parameters
Name Type Description
$distance integer
Returns
Type Description
float
methodpublictf( float $freq ) : float
abstract

Computes a score factor based on a term or phrase's frequency in a document. This value is multiplied by the idf(Term, Searcher) factor for each term in the query and these products are then summed to form the initial score for a document.

Terms and phrases repeated in a document indicate the topic of the document, so implementations of this method usually return larger values when 'freq' is large, and smaller values when 'freq' is small.

freq - the frequency of a term within a document Returns a score factor based on a term's within-document frequency

Parameters
Name Type Description
$freq float
Returns
Type Description
float
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