Using Perl with XML (part 1) - Getting Down To Business (
Page 2 of 7 )
Before we get into the nitty-gritty of XML
parsing with Perl, I'd like to take some time to explain how all the pieces fit
together.
In case you don't already know, XML is a markup language
created to help document authors describe the data contained within a document.
This description is accomplished by means of tags, very similar in appearance to
regular HTML markup. However, where HTML depends on pre-defined tags, XML allows
document authors to create their own tags, immediately making it more powerful
and flexible. There are some basic rules to be followed when creating an XML
file, and a file can only be processed if these rules are followed to the
letter.
Once a file has been created, it needs to be converted, or
"transformed", from pure data into something a little more readable. XSL, the
Extensible Style Language, is typically used for such transformations; it's a
powerful language that allows you to generate different output from the same XML
data source. For example, you could use different XSL transformations to create
an HTML Web page, a WML deck, and an ASCII text file...all from the same source
XML.
There's only one problem here: most browsers don't come with an XML
parser or an XSL processor. The latest versions of Internet Explorer and
Netscape Gecko do support XML, but older versions don't. And this brings up an
obvious problem: how do you use an XML data source to generate HTML for these
older browsers?
The solution is to insert an additional layer between the
client and the server, which takes care of parsing the XML and returning the
rendered output to the browser. And that's where Perl comes in - it supports XML
parsing, through add-on DOM and XML packages, and even has a package to handle
XSL transformations through the Sablotron processor.
As I've said
earlier, there are two methods to parse XML data with Perl, and each one has
advantages and disadvantages. I'll explain both approaches, together with simple
examples to demonstrate how to use them in your own applications.
