Search/Lucene/Search/Similarity.php

category: Zend
copyright: Copyright (c) 2005-2010 Zend Technologies USA Inc. (http://www.zend.com)
license: http://framework.zend.com/license/new-bsd New BSD License
package: Zend_Search_Lucene
subpackage: Search
version: $Id: Similarity.php 20096 2010-01-06 02:05:09Z bkarwin $
Classes: Zend_Search_Lucene_Search_Similarity

Description

Zend Framework

LICENSE

This source file is subject to the new BSD license that is bundled with this package in the file LICENSE.txt. It is also available through the world-wide-web at this URL: http://framework.zend.com/license/new-bsd If you did not receive a copy of the license and are unable to obtain it through the world-wide-web, please send an email to license@zend.com so we can send you a copy immediately.

Zend_Search_Lucene_Search_Similarity
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category: Zend
copyright: Copyright (c) 2005-2010 Zend Technologies USA Inc. (http://www.zend.com)
license: http://framework.zend.com/license/new-bsd New BSD License
package: Zend_Search_Lucene
subpackage: Search
Properties: $_defaultImpl; $_normTable
Methods: setDefault; getDefault; lengthNorm; queryNorm; decodeNorm; encodeNorm; _floatToByte; tf; sloppyFreq; idf; idfFreq; coord

Description

Properties

$_defaultImpl
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Zend_Search_Lucene_Search_Similarity $_defaultImpl = ''

The Similarity implementation used by default.

Details

$_defaultImpl: Zend_Search_Lucene_Search_Similarity
visibility: private
default
final: false
static: true

$_normTable
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array $_normTable = 'array'

Cache of decoded bytes.

Array of floats

Details

$_normTable: array
visibility: private
default: array
final: false
static: true

Methods

_floatToByte
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_floatToByte(
           $f
          )
        
        :
        float

Float to byte conversion

Arguments

$f

Output

float

Details

visibility: private
final: false
static: true

coord
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coord(
          integer $overlap, integer $maxOverlap
          )
        
        :
        float

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

Arguments

$overlap: integer
$maxOverlap: integer

Output

float

Details

visibility: public
final: false
static: false

decodeNorm
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decodeNorm(
          integer $byte
          )
        
        :
        float

Decodes a normalization factor stored in an index.

Arguments

$byte: integer

Output

float

Details

visibility: public
final: false
static: true

encodeNorm
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encodeNorm(
          float $f
          )
        
        :
        integer

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.

Arguments

$f: float

Output

integer

Details

visibility: public
final: false
static: true

getDefault
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getDefault(
          
          )
        
        :
        Zend_Search_Lucene_Search_Similarity

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

Output

Zend_Search_Lucene_Search_Similarity

Details

visibility: public
final: false
static: true

idf
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idf(
          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

Arguments

$input: mixed
$reader: Zend_Search_Lucene_Interface

Output

a: score factor for the term

Details

visibility: public
final: false
static: false

idfFreq
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idfFreq(
          integer $docFreq, integer $numDocs
          )
        
        :
        float

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

Arguments

$docFreq: integer
$numDocs: integer

Output

float

Details

visibility: public
final: false
static: false

lengthNorm
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lengthNorm(
          string $fieldName, integer $numTokens
          )
        
        :
        float

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

Arguments

$fieldName: string
$numTokens: integer

Output

float

Details

visibility: public
final: false
static: false

queryNorm
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queryNorm(
          float $sumOfSquaredWeights
          )
        
        :
        float

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

Arguments

$sumOfSquaredWeights: float

Output

float

Details

visibility: public
final: false
static: false

setDefault
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setDefault(
          Zend_Search_Lucene_Search_Similarity $similarity
          )
        
        :

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

Arguments

$similarity: Zend_Search_Lucene_Search_Similarity

Details

visibility: public
final: false
static: true

sloppyFreq
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sloppyFreq(
          integer $distance
          )
        
        :
        float

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

Arguments

$distance: integer

Output

float

Details

visibility: public
final: false
static: false

tf
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tf(
          float $freq
          )
        
        :
        float

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

Arguments

$freq: float

Output

float

Details

visibility: public
final: false
static: false

API Documentation

Search/Lucene/Search/Similarity.php

Description

Zend_Search_Lucene_Search_Similarityjump to top

Description

Properties

$_defaultImpljump to class

Details

$_normTablejump to class

Details

Methods

_floatToBytejump to class

Arguments

Output

Details

coordjump to class

Arguments

Output

Details

decodeNormjump to class

Arguments

Output

Details

encodeNormjump to class

Arguments

Output

Details

getDefaultjump to class

Output

Details

idfjump to class

Arguments

Output

Details

idfFreqjump to class

Arguments

Output

Details

lengthNormjump to class

Arguments

Output

Details

queryNormjump to class

Arguments

Output

Details

setDefaultjump to class

Arguments

Details

sloppyFreqjump to class

Arguments

Output

Details

tfjump to class

Arguments

Output

Details

Zend_Search_Lucene_Search_Similarity
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$_defaultImpl
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$_normTable
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_floatToByte
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coord
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decodeNorm
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encodeNorm
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getDefault
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idf
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idfFreq
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lengthNorm
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queryNorm
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setDefault
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sloppyFreq
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tf
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