Web Services - Guide to Cloud Computing for Business and Technology Managers - page 174

format for exchanging messages (SOAP), a common service specification
format (WSDL), a common means for service lookup (UDDI), and a stan-
dard that specifically deals with interoperability issues (WS-I Basic Profile).
Examples of technology development include further development of the
ideas behind ESB, so as to be able to handle the different protocols for the
service provider and service consumer, and further development of regis-
tries for easy registration and discovery of services.
Web Services are a set of integration technology standards that were
designed specifically to meet the requirements arising from service-
oriented architectures and systems. In many ways, Web Services are
really not much different from existing middleware technologies, but
they do differ in their focus on simplicity and interoperability. The most
important feature offered by Web Services is that all major software ven-
dors have agreed to support them. Interoperability is still not, of course,
guaranteed to be painless but at least the problems encountered will be
bugs and misinterpretations of common standards, not intentionally
introduced incompatibilities between similar but different proprietary
technologies.
All application integration technologies, including Web Services, really
only provide four basic functions that let developers (and programs) do the
following:
1. Find suitable services (using UDDI or another directory)
2. Find out about a service (using WSDL)
3. Ask a service to do something (using SOAP)
4. Make use of services such as security (using WS-* standards)
SOAP, WSDL, and UDDI were the first Web Service standards to be pub-
lished, but they only meet the most basic requirements for application inte-
gration. They lack support for security, transactions, reliability, and many
other important functions. This gap is being progressively filled by a series
of standards (commonly called WS-* ) first outlined by IBM and Microsoft
at a W3C workshop in 2001. The task of creating these additional standards
and getting industry-wide agreement is a confusing work in progress, with
specifications in varying degrees of maturity and supported by various stan-
dards bodies. Some specifications complement, overlap, and compete with
each other. There are now however production-ready implementations avail-
able for many of them. See http://www.w3.org/2002/ws/ for some insights
into these specifications.
Web Services are XML standards. Services are defined using XML, and
applications request services by sending XML messages and the Web Service
standards make extensive use of other existing XML standards wherever pos-
sible. There are multiple Web Service standards, and these can be organized
into various categories. This number of standards may suggest complexity