HTML and CSS Reference
a hundred different vendors to quote you a system. If you extend that
model to include almost anything you can shop forfrom cars to hot tub-
sXML provides an elegant base layer of communication among cooper-
ating vendors on the Internet.
Almost any data that is captured and stored can more easily be shared
using XML. For many systems, the XML DTDs may define a data-transfer
protocol and nothing more. The data may never actually be stored using
the XML-defined markup; it may exist in an XML-compatible form only
long enough to pass on the wire between two systems.
One increasingly popular use of XML is web services, which make it pos-
sible for diverse applications to discover each other and exchange data
seamlessly over the Internet, regardless of their programming language
or architecture. For more information on web services, consult Web Ser-
vices Essentials by Ethan Cerami (O'Reilly).
In conjunction with XML-based data exchange, the Extensible Stylesheet
Language, or XSL, is increasingly being used to describe the appearance
and definition of the data represented by these XML DTDs. Much like
Cascading Style Sheets (CSS) and its ability to transform HTML doc-
uments, XSL supports the creation of stylesheets for any XML DTD.
You can use CSS with XML documents as well, but it is not as pro-
grammatically rich as XSL. While CSS stops with stylesheets, XSL is a
style language. XSL certainly addresses the need for data display, and
it provides rich tools that allow data represented with one DTD to be
transformed into another DTD in a controlled and deterministic fashion.
A complete discussion of XSL is beyond the scope of this topic; consult
XSLT by Doug Tidwell (O'Reilly) for complete details.
The potential for XML goes well beyond that of traditional markup and
presentation tools. What we now see and use in the XML world is only
scratching the surface of the potential for this technology.
15.8.4. Standardizing HTML
Last, but certainly not least, the W3C uses XML to define a standard ver-
sion of HTML known as XHTML. XHTML retains almost all of the features