Perl in a Nutshell, 2nd Edition

Chapter 13. XML and Perl

The Extensible Markup Language (XML) is a metalanguage for providing complete, configurable information for documents and other types of data. XML is based loosely on SGML, but has divorced itself of much of the complexity that made SGML unsuitable for everyday use. Without opening a can of worms about the differences between SGML and XML, suffice it to say that SGML is the predecessor to XML, and XML is a subset of SGML, with extensions.

With XML, you aren’t bound by a fixed format, but can mark up a document to make it easily adaptable to whatever final format you later decide to apply it to. In fact, this book is written in XML, to be produced later not only in a print format but in an online format as well.

XML is often associated with web content, but it is much more flexible than that. Lately, XML’s application to web services such as SOAP and XML-RPC has given it a chance to flex its muscles and show what it’s capable of. XML gives you the structure to hold any content you’d like, whether it be the pages of this book in their rawest form, a list of your favorite recipes, or the ledger from your checkbook. XML is structured so that you can represent any kind of data in XML. XML’s openness means that you can implement an XML-based application on any platform.

This chapter is focused on parsing, checking and delivering XML content. Chapter 14 covers SOAP programming in XML.