XML Processors (Perl and XML)

1.3. XML Processors

Now that you see the easy side of XML, we will expose some of XML's quirks. You need to consider these quirks when working with XML and Perl.

When we refer in this book to an XML processor (which we'll often refer to in shorthand as a processor, not to be confused with the central processing unit of a computer system that has the same nickname), we refer to software that can either read or generate XML documents. We use this term in the most general way -- what the program actually does with the content it might find in the XML it reads is not the concern of the processor itself, nor is it the processor's responsibility to determine the origin of the document or decide what to do with one that is generated.

As you might expect, a raw XML processor working alone isn't very interesting. For this reason, a computer program that actually does something cool or useful with XML uses a processor as just one component. It usually reads an XML file and, through the magic of parsing, turns it into in-memory structures that the rest of the program can do whatever it likes with.

In the Perl world, this behavior becomes possible through the use of Perl modules: typically, a program that needs to process XML embraces, through the use pragma, an existing package that makes a programmer interface available (usually an object-oriented one). This is why, before they get down to business, many XML-handling Perl programs start out with use XML::Parser; or something similar. With one little line, they're able to leave all the dirty work of XML parsing to another, previously written module, leaving their own code to decide what to do pre- and post-processing.