published about 1 year ago (27.03.2007 07:43)

extending PHP's SimpleXML

PHP’s XML workhorse, SimpleXML can be extended. you can supply a class of your own for PHP to wrap all XML nodes instead of the default SimpleXMLElement. do this by passing the desired class name as a string to the simplexml_load_(file|string) methods: 

<?php

class MySimpleXMLElement extends SimpleXMLElement
{     
   // extending parent method
   public function xpath($path)
   {  
      echo "evaluating the following xpath expression: $path\n";
      $result = parent::xpath($path);
      echo "found " . sizeof($result) . " nodes";
      return $result;
   }
}

$doc = simplexml_load_file('products.xml', 'MySimpleXMLElement');
// calling an extended method
$nodes = $doc->xpath('//articles/article/shortdesc');
echo "\n";

// calling a parent method
echo $doc->root->getName();
echo "\n";

?>

i didn’t poke around in the internals of the parent class too much, no idea how well that would. on the other hand, in many cases it might be a better solution to delegate to SimpleXML instead of inheriting and extending from it.

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published about 1 year ago (18.03.2007 11:20)

ruby: performance comparison of rexml and libxml

update: here’s the same for PHP’s XML Parser.

a quick comparison of the two libraries available for processing XML in ruby shows dramatic performance differences.

am i missing something, is there a fundamental flaw in the test? of course REXML is pure ruby, while libxml is C; but can the difference really be so huge?

loading an xml file

file size libxml REXML factor
10KB 0,83 39,17 47,0
100KB 6,67 306,56 46,0
1.6MB 71,88 3954,21 55,0

simple xpath expression

file size libxml REXML factor
10KB 0,12 124,68 1004,7
100KB 0,67 678,11 1016,8
1.6MB 6,21 22578,18 3633,6

the test code

def benchmark
   start = Time.new.to_f
   10.times { yield }
   puts ((Time.new.to_f - start) / 10) * 1000
end

doc = nil

# exclude the effect of filesystem caching (makes sense?)
File.read('products.xml')

#
# libxml
#
require 'rubygems'
require 'xml/libxml'

benchmark do
   doc = XML::Document.file("products.xml")
end

benchmark do
   doc.find('//articles/article/shortdesc').each do |node|
      #puts node.content
   end
end

#
# rexml
#
require "rexml/document"

benchmark do
   doc = REXML::Document.new File.read("products.xml")
end

benchmark do
   doc.elements.each("//articles/article/shortdesc") do |node| 
      #puts node.text
   end
end

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