Web Services - Guide to Cloud Computing for Business and Technology Managers - page 176

use mechanisms provided by WS-Security to protect sensitive information
intended only for the credit card application, hiding it from the router that
the message must pass through on its journey.
We start our discussion of standards with the Extensible Markup Language
(XML) because XML forms the basis on which most of the other standards
are built.
8.2 XML
John Bosak of Sun Microsystems is credited with the revolutionary work on
eXtensible Markup Language (XML). The idea of XML essentially emerged
from the other nonexpendable markup languages such as Generalized
Markup Language (GML) from IBM, Standardized Generalized Markup
Language (SGML) from ISO, and Hypertext Markup Language (HTML)
from ECRN. XML's popularity essentially stems out of its extensible capa-
bility. One of the biggest contributions of XML is its capability of interop-
erability. The development of XML resulted in its adoption by a variety of
industries—both vertical and horizontal. This has resulted in the creation of
a large number of XML vocabularies that cater to the interoperability needs
of different industries. But the biggest impact of XML for enterprise solution
has as a part of the SOAP, WSDL, and UDDI technologies.
XML is probably the most important of the standards on which Web
Services are built. XML documents are often used as a means for passing
information between the service provider and the service consumer. XML
also forms the basis for WSDL (Web Services Description Language), which
is used to declare the interface that a Web Service exposes to the consumer
of the service. Additionally, XML underlies the SOAP protocol for access-
ing a Web Service. Lastly, UDDI (Universal Description, Discovery, and
Integration), which is used to publish and discover a Web Service, is also
based on XML. Similar to HTML, XML uses tags. However, unlike HTML,
where tags are used to indicate how the data should be presented or dis-
played, in XML, tags are used to describe what the data are. Another dif-
ference from HTML is that tags are not fixed but can be invented whenever
there is a need for a new one.
XML has been adopted as a popular middleware-independent standard
format for the exchange of data and documents. XML is basically the lowest
common denominator upon which the IT industry can agree. Unlike CORBA,
IDL, and Java interfaces, XML is not bound to any particular technology or
middleware standard and is often used today as an ad hoc format for process-
ing data across different, largely incompatible middleware platforms. XML is
free and comes with a large number of tools on many different platforms,
including different open source parsing APIs such as SAX, StAX, and DOM.