The Role of XML
XML is a metalanguage (literally a language about languages) defined by the World Wide Web Consortium (W3C), one of the main organizations driving the push to open Web standards. In its simplest sense, XML is a set of rules and guidelines for describing structured data in plain text rather than proprietary binary representations. However, as a phenomenon, XML goes beyond its technical specification. Since its standardization by the W3C in 1998, XML has been the driving force behind numerous other standards and vocabularies that are forging a fundamental change in the software world.
In its short history, XML has given rise to numerous vertical industry vocabularies in support of B2B e-commerce, horizontal vocabularies that provide services to a wide range of industries, and XML protocols that have used XML's simple power of combination to open up new possibilities for doing distributed computing. As Figure 1.2 shows, XML's influence has been felt in three waves, from industry-specific vocabularies, to horizontal industry applications, to protocols that describe how businesses can exchange data across the Web. One of the key developments has been SOAP, the protocol that has opened the Web to program-to-program communication and, as we'll see in Chapter 5, is the basis for Web services.
Figure 1.2 XML has been widely used as a language for a variety of applications ranging from vertical industry vocabularies, to horizontal industry applications, to protocols. XML data vocabularies XML vocabularies that provide functionality for a variety of industries XML vocabularies that define protocols for moving data across the Web