Page 215 - DCAP312_WEB_TECHNOLOGIES_II

Unit 10: Web Services

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10.2 XML Web Services

XML Web services are the fundamental building blocks in the move to distributed computing
on the Internet. Open standards and the focus on communication and collaboration among
people and applications have created an environment where XML Web services are becoming
the platform for application integration. Applications are constructed using multiple XML Web
services from various sources that work together regardless of where they reside or how they
were implemented.
There are probably as many definitions of XML Web Service as there are companies building
them, but almost all definitions have these things in common:
• XML Web Services expose useful functionality to Web users through a standard Web
protocol. In most cases, the protocol used is SOAP.
• XML Web services provide a way to describe their interfaces in enough detail to allow a
user to build a client application to talk to them. This description is usually provided in
an XML document called a Web Services Description Language (WSDL) document.

• XML Web services are registered so that potential users can find them easily. This is done
with Universal Discovery Description and Integration (UDDI).
One of the primary advantages of the XML Web services architecture is that it allows programs
written in different languages on different platforms to communicate with each other in a
standards-based way. Those of you who have been around the industry a while are now saying,
How is this any different?” The first difference is that SOAP is significantly less complex than
earlier approaches, so the barrier to entry for a standards-compliant SOAP implementation is
significantly lower which at last count contained 79 entries. You will find SOAP implementations
from most of the big software companies, as you would expect, but you will also find many
implementations that are built and maintained by a single developer. The other significant
advantage that XML Web services have over previous efforts is that they work with standard
Web protocols—XML, HTTP and TCP/IP. A significant number of companies already have a
Web infrastructure, and people with knowledge and experience in maintaining it, so again, the
cost of entry for XML Web services is significantly less than previous technologies.

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