InformationWeek

Data exchange between applications can be done more efficiently with XML. And it enables interactions across platforms that otherwise share no common data formats. This makes it especially useful in distributed application development, in which applications are split into tiers of logically related code that usually execute on different machines, often running different operating systems. Because XML is platform independent, the different tiers can exchange data using its features.

XML is also being used to control and execute code in the different tiers, acting as the glue that integrates application components. In this role, it acts as a gateway between autonomous, heterogeneous systems. (For a look at this use of XML, see Don Box's "Lessons from the Component Wars: An XML Manifesto" at msdn.microsoft.com/xml/articles/xmlmanifesto.asp.)

But for XML to reach its fullest potential, everyone must agree to use the language in the same ways. This means that both the sending and the receiving parties must agree to use a particular schema, a way of describing data using XML notation. To accomplish this, applications will need additional standards from the World Wide Web Consortium (W3C), some of which are just in the early proposal stages.

XML will fully blossom into a valuable technology for E-commerce when industry groups work together to define XML schemas to describe industry data. For example, participants in an industrywide E-marketplace might define a schema with the specific tags needed to encapsulate information on the customers, products, and services that form the basis of their transactions. These schemas would have to be agreed upon and shared by the people and companies that use them.

One such initiative is Microsoft's BizTalk (www.biztalk.org), a platform for launching the company's BizTalk Server. Microsoft is defining the BizTalk Framework, a set of guidelines for publishing schemas in XML and using XML messages to integrate software programs. The BizTalk Server, available as a technology preview, provides Internet application integration using XML and the BizTalk Framework. It includes secure and reliable data delivery, routing and transformation of business documents, and development tools for existing applications.

The Mathematical Markup Language is one of the earliest XML schemas. It was developed to describe mathematical notation, including structure and content, letting content be served, received, and processed on the Web.

The Organization for the Advancement of Structured Information Standards sponsors www.xml.org. This site features a wealth of information about XML and its uses, as well as an impressive catalog of XML schemas by industry group. The site provides a registry and repository for XML schemas and other public resources. Industry groups can register their XML data-exchange specifications, individuals can look for specifications in their areas of interest, and applications can access the XML resources needed to act on an XML document.

XHTML is the latest of recent XML-related standards work published by the W3C (see story, "XHTML: A Bridge To The Future"). In early April, the consortium published the latest working draft of XML Schema, which provides a means for defining the structure, content, and semantics of XML documents, using an inventory of XML markup constructs. This working draft arose from several proposals received by the W3C, including XML-Data, which was spearheaded by Microsoft, Document Content Description for XML, and others.

The XForms 1.0 working draft defines the next generation of Web forms that capture the device-independent data model and logic of form-based Web applications. These new forms will encompass an explicit data model that defines the form as a composite data type with constraints on values. The model also defines the user interface, expressed as a set of presentation controls bound to the data model, and the use of XML and Unicode for exchanging form data with servers.

The Extensible Stylesheet Language, which is used to express style sheets on the Web, is nearing completion as an official W3C recommendation. The two parts of XSL provide a language for transforming XML documents and a vocabulary for specifying formatting.

The W3C has received a number of proposals related to XML that it has published as Notes, which are preliminary documents meant to begin discussion. Recent Notes include XML Japanese Profile for expressing Japanese characters in XML, and the XML Document Navigation Language for content navigation in a variety of devices.