450 SOA Solutions Using IBM Information Server
Using open standards provides broad interoperability among different vendor
solutions. These principles permit companies to implement Web services without
having any knowledge of the service consumers, and vice versa. This facilitates
just-in-time integration and allows businesses to establish new partnership easily
and dynamically.
A.2.1 What Web services are
The W3C’s Web Services Architecture Working Group has the following working
definition of a Web service:
“A Web service is a software application identified by a URI, whose interfaces
and bindings are capable of being defined, described, and discovered as
XML artifacts. A Web service supports direct interactions with other software
agents using XML-based messages exchanged via Internet-based protocols.
Basic Web services combine the power of two ubiquitous technologies: XML, the
universal data description language; and the HTTP transport protocol widely
supported by browser and Web servers:
Web services = XML + transport protocol (such as HTTP)
Some of the key features of Web services are as follows:
򐂰 Web services are self-contained.
On the client side, no additional software is required. A programming
language with XML and HTTP client support, for example, is enough to get
you started. On the server side, a Web server and a servlet engine are
required. It is possible to Web service enable an existing application without
writing a single line of code.
򐂰 Web services are self-describing.
Neither the client nor the server knows or cares about anything besides the
format and content of request and response messages (loosely coupled
application integration).
The definition of the message format travels with the message. No external
metadata repositories or code generation tools are required.
򐂰 Web services are modular.
Web services is a technology for deploying and providing access to business
functions over the Web — J2EE, CORBA, and other standards are
technologies for implementing these Web services.
Appendix A. Service Oriented Architecture (SOA) overview 451
򐂰 Web services can be published, located, and invoked across the Web.
The standards required to do so are:
Simple Object Access Protocol (SOAP), also known as service-oriented
architecture protocol, an XML-based RPC and messaging protocol
Web Service Description Language (WSDL), a descriptive interface and
protocol binding language
Universal Description, Discovery, and Integration (UDDI), a registry
mechanism that can be used to look up Web service descriptions
򐂰 Web services are language independent and interoperable.
The interaction between a service provider and a service requester is
designed to be completely platform and language independent. This
interaction requires a WSDL document to define the interface and describe
the service, along with a network protocol (usually HTTP). Because the
service provider and the service requester have no idea what platforms or
languages the other is using, interoperability is a given.
򐂰 Web services are inherently open and standards based.
XML and HTTP are the technical foundation for Web services. A large part of
the Web service technology has been built using open source projects.
Therefore, vendor independence and interoperability are realistic goals.
򐂰 Web services are dynamic.
Dynamic e-business can become a reality using Web services because, with
UDDI and WSDL, the Web service description and discovery can be
automated.
򐂰 Web services are composable.
Simple Web services can be aggregated to more complex ones, either using
workflow techniques or by calling lower-layer Web services from a Web
service implementation.
Figure A-10 shows a typical Web service collaboration that is based on the SOA
model shown previously in Figure A-7 on page 445.

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