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description. When processes span business boundaries, loose coupling
based on precise external protocols is required because the parties involved
do not share application and workflow implementation technologies and
will not allow external control over the use of their back-end applications.
Such business interaction protocols are by necessity message centric; they
specify the flow of messages representing business actions among trad-
ing partners, without requiring any specific implementation mechanism.
With such applications, the loosely coupled, distributed nature of the Web
enables exhaustive and full orchestration, choreography, and monitoring
of the enterprise applications that expose the Web Services participating in
the message exchanges.
Web Services provide standard and interoperable means of integrating
loosely coupled web-based components that expose well-defined inter-
faces, while abstracting the implementation- and platform-specific details.
Core Web Service standards such as SOAP, WSDL, and UDDI provide a
solid foundation to accomplish this. However, these specifications primarily
enable the development of simple Web Service applications that can conduct
simple interactions. However, the ultimate goal of Web Services is to facili-
tate and automate business process collaborations both inside and outside
enterprise boundaries. Useful business applications of Web Services in EAI
and business-to-business environments require the ability to compose com-
plex and distributed Web Service integrations and the ability to describe the
relationships between the constituent low-level services. In this way, collab-
orative business processes can be realized as Web Service integrations.
A business process specifies the potential execution order of operations
originating from a logically interrelated collection of Web Services, each
of which performs a well-defined activity within the process. A business
process also specifies the shared data passed between these services, the
external partners' roles with respect to the process, joint exception handling
conditions for the collection of Web Services, and other factors that may
influence how Web Services or organizations participate in a process. This
would enable long-running transactions between Web Services in order to
increase the consistency and reliability of business processes that are com-
posed out of these Web Services.
The orchestration and choreography of Web Services is enabled under three
specification standards, namely, the Business Process Execution Language
for Web Services (BPEL4WS or BPEL for short), WS-Coordination (WS-C),
and WS-Transaction (WS-T). These three specifications work together to form
the bedrock for reliably choreographing Web Service-based applications,
providing BPM, transactional integrity, and generic coordination facilities.
BPEL is a workflow-like definition language that describes sophisticated
business processes that can orchestrate Web Services. WS-Coordination and
WS-Transaction complement BPEL to provide mechanisms for defining spe-
cific standard protocols for use by transaction processing systems, workflow
systems, or other applications that wish to coordinate multiple Web Services.
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