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Chapter 1. XML overview 13
XSLT has become a critical part of Web applications, because it allows versatility
in the presentation logic. W3C has published a working draft for XSLT Version 2.0
and XML Path Language (XPath) Version 2.0 in April 2002. The later had a major
IBM involvement.
1.8 Web services and XML
Web services have gained prominence in the last three years. They are the new
middleware that will glue all kinds of disparate applications from different
vendors. Presently, there are a few major vendors touting middleware: TIBCO,
BEA eLink/Tuxedo and IBM’s MQ-series. Web services on the other hand are not
proprietary. They are self-contained, modular applications, self explanatory
applications that are published on the Web. They provide functions that
encapsulate anything from single functions to complex business functions. An
example of a simple function may be a calculator, spreadsheet, or a tutorial. An
example complex functions could be the processing of a tax return, stock quotes,
or processing credit card transactions. Once this Web service has been
deployed, anyone (be it another application or Web service) would be able to
locate and invoke it.
When we discuss Web services, we involve a few components:
Simple Object Access Protocol (SOAP) is an XML-based protocol that allows
applications to invoke applications provided by service provides anywhere on the
Web. It is supported by HTTP, and therefore, can be run on the Internet without
any new requirements over existing infrastructure. It is independent off any
programming language and component technology, and is object neutral. It is
also independent of operating systems.
Universal Description Discovery and Integration (UDDI) is a specification for
Web registries of Web services. Web users locate and discover services on a
UDDI-based registry. There are registries of services distributed over the
Internet, and these registry of services are described in a common XML format
or schema. For a common format, searching and analysis of applications would
be made much easier. A UDDI registry has been made available from IBM’s
alphaWorks Web site, and supports users in various department- or
company-wide scenarios.
Web Services Description Language (WSDL) is a language that is used to
describe a service to the world. The definition of WSDL is:
“WSDL is an XML format for describing network services as a set of
end-points operating on messages containing either document-oriented or
procedure-oriented information. The operations and messages are described
abstractly, and then bound to a concrete network protocol and message