Web Services - Guide to Cloud Computing for Business and Technology Managers - page 184

card catalog used for recording the arrival of new topics and other media as
well as looking up topics and other media. Another common analogy is the
telephone system's Yellow Pages, used by service providers to publish their
services and by service consumers to find services.
The Universal Description, Discovery, and Integration (UDDI) specifica-
tion defines a standard way of registering, deregistering, and looking up
services. Figure 9.n shows how UDDI enables the dynamic description, dis-
covery, and integration of services. A service provider first registers a service
with the UDDI registry. A service consumer looks up the required service in
the UDDI registry. Then, when it finds the required service, the consumer
directly binds with the provider to use the service.
The role of the UDDI registry in Web Services is similar to the role played by
a search engine on the Internet. The power of the search engine comes from
the keywords used to classify content. In a similar manner, a fine-grained
search for a Web Service is possible only if a service is classified properly.
The classification and identification taxonomies present in the UDDI registry
provide a starting point for describing Web Services. Equally important is
the classification of the businesses and organizations that offer Web Services.
SOAP services that are normally described using WSDL (Web Services
Description Language) can be located by searching a UDDI (Universal
Description, Discovery, and Integration) directory. Services can describe
their requirements for things like security and reliability using policy state-
ments, defined using the WS-Policy framework, and specialized policy stan-
dards such as WS-SecurityPolicy. These policies can be attached to a WSDL
service definition or kept in separate policy stores and retrieved using WS
MetadataExchange.
UDDI has proven to be the least used so far of the original three Web
Service standards. Organizations are developing large complex Web Service
systems today without the use of global UDDI directories, using other meth-
ods of finding services such as personal contact or published lists of services
on websites. This could all change in the future, especially when industry
associations start releasing common service definitions and need to publish
directories of qualified service providers.
8.6 Security, Transactions, and Reliability
One of the problems faced by most middleware protocols is that they do not
work well on the open Internet because of the connectivity barriers imposed
by firewalls. Most organizations do not want outsiders to have access to
the protocols and technologies they use internally for application integra-
tion and so block the necessary TCP/IP ports at their perimeter firewalls.
The common technology response to this problem, and the one adopted by