org.apache.nutch.crawl
Class TextProfileSignature

java.lang.Object
  org.apache.hadoop.conf.Configured
      org.apache.nutch.crawl.Signature
          org.apache.nutch.crawl.TextProfileSignature

All Implemented Interfaces:

Configurable

public class TextProfileSignature
extends Signature

An implementation of a page signature. It calculates an MD5 hash of a plain text "profile" of a page. In case there is no text, it calculates a hash using the MD5Signature.

The algorithm to calculate a page "profile" takes the plain text version of a page and performs the following steps:

• remove all characters except letters and digits, and bring all characters to lower case,
• split the text into tokens (all consecutive non-whitespace characters),
• discard tokens equal or shorter than MIN_TOKEN_LEN (default 2 characters),
• sort the list of tokens by decreasing frequency,
• round down the counts of tokens to the nearest multiple of QUANT (QUANT = QUANT_RATE * maxFreq, where QUANT_RATE is 0.01f by default, and maxFreq is the maximum token frequency). If maxFreq is higher than 1, then QUANT is always higher than 2 (which means that tokens with frequency 1 are always discarded).
• tokens, which frequency after quantization falls below QUANT, are discarded.
• create a list of tokens and their quantized frequency, separated by spaces, in the order of decreasing frequency.

This list is then submitted to an MD5 hash calculation.

Author:

Andrzej Bialecki <ab@getopt.org>

Constructor Summary

TextProfileSignature()

Method Summary

byte[]	calculate(WebPage page)
Collection<WebPage.Field>	getFields()

Methods inherited from class org.apache.hadoop.conf.Configured

getConf, setConf

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TextProfileSignature

public TextProfileSignature()

Method Detail

calculate

public byte[] calculate(WebPage page)

Specified by:

calculate in class Signature

getFields

public Collection<WebPage.Field> getFields()

Specified by:

getFields in class Signature