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244 10 Transforming with Traditional Programming Languages

use XML::DOM;

$p = new XML::DOM::Parser;

$doc = $p->parsefile($ARGV[0]);

$weights = $doc->getElementsByTagName(Weight);

for ($i = 0; $i < $weights->getLength; $i++) {

$weight =

$weights->item($i)->getFirstChild->getNodeValue;

print("Weight $weight\n");

}

Program 10.17 Converting an entire XML document using a Perl data structure

10.2.3 The Document Object Model

Although transforming XML element by element is capable of accomplishing

any transformation task, it gets very complicated very quickly. The problem

is that the information one needs at a given time might not be in the element

being processed. It may, for example, be in the parent element. To deal with

this, one can parse the entire document and then extract the parts that are

needed. For example, suppose that one would like to extract the date, height,

and weight of each interview. Program 10.17 uses the “whole document” ap-

proach to this task. This program uses the XML::DOM package. DOM stands

for document object model. It reads an entire XML document into a single

module object. Just as in the XML::Parser package, one constructs a parser,

but no handlers need to be defined. The parser is then invoked to parse a

document, and the module object containing the document is assigned to

thedocvariable. After that, one extracts information about the document

by using DOM methods.

There are many DOM methods. One of the most popular methods is

getElementsByTagNamewhich extracts all of the elements within the cur-

rent element which have a particular tag. Most DOM methods return an

object, so one uses the->operator to extract information from it. Theitem

method gets one of the elements extracted bygetElementsByTagName.

Theitemmethod is yet another way to extract one of the items in a list. One

uses brackets to get one item in an array, and braces to get one item in a hash.