| The Extensible Markup Language (XML) is a document-processing standard that is an official recommendation of the World Wide Web Consortium (W3C), the same group responsible for overseeing the HTML standard. Many expect XML and its sibling technologies to become the markup language of choice for dynamically generated content, including nonstatic web pages. Many companies are already integrating XML support into their products. XML is actually a simplified form of Standard Generalized Markup Language (SGML), an international documentation standard that has existed since the 1980s. However, SGML is extremely complex, especially for the Web. Much of the credit for XML's creation can be attributed to Jon Bosak of Sun Microsystems, Inc., who started the W3C working group responsible for scaling down SGML to a form more suitable for the Internet. Put succinctly, XML is a metalanguage that allows you to create and format your own document markups . With HTML, existing markup is static: <HEAD> and <BODY>, for example, are tightly integrated into the HTML standard and cannot be changed or extended. XML, on the other hand, allows you to create your own markup tags and configure each to your likingfor example, <HeadingA>, <Sidebar>, <Quote>, or <ReallyWildFont>. Each of these elements can be defined through your own document type definitions and stylesheets and applied to one or more XML documents. XML schemas provide another way to define elements. Thus, it is important to realize that there are no correct tags for an XML document, except those you define yourself. While many XML applications currently support Cascading Style Sheets (CSS), a more extensible style sheet specification exists, called the Extensible Stylesheet Language (XSL). With XSL, you ensure that XML documents are formatted the same way no matter which application or platform they appear on. XSL consists of two parts : XSLT ( transformations ) and XSL-FO ( formatting objects ). Transformations, as discussed in this book, allow you to work with XSLT and convert XML documents to other formats such as HTML. Formatting objects is described briefly later in this chapter. This chapter offers a quick overview of XML, as well as some sample applications that allow you to get started in coding. We won't cover everything about XML. Some XML- related specifications are still in flux as this book goes to print. However, after reading this book, we hope that the components that make up XML will seem a little less foreign.  |
