Information Technology Reference
In-Depth Information
Working right on top of Web services, BPEL relies on the primitive Web
service standards, the Web service description language (WSDL), which
unii es service interface description, and the simple object access protocol
(SOAP), which regulates service messaging, to engineer service orchestra-
tion. Grid services, for example, those developed with Globus toolkits or
available with OMII distribution, can be orchestrated with BPEL in the
exact same way as standard Web services given conformance to the same
standards.
The proposal of BPEL was initially submitted to the OASIS (Organization
for the Advancement of Structured Information Standard) in April 2003
by IBM, Microsoft, and other industrial partners, while the origin of the
language can actually be traced back to IBM's Web service l ow language
(WSFL) and Microsoft's XLANG, both of which were part of the process
management solutions built into the companies' commercial servers. At
present, BPEL is mainly seen in two versions: the early BPEL4WS 1.1 and
the latest WS-BPEL 2.0 published on 11 April 2007. The name change voted
in the autumn of 2004 aligned with the Web service standard naming
conventions. From then on, signii cant enhancements have been able to
merge into the language with requirements and features raised by the
BPEL community over the years since its i rst release. Companies like
ActiveEndpoints, Adobe, Deloitte, JBoss, TIBCO, WebMethods, Oracle, and
others, which have contributed to the standardization of the new spec-
ii cation, have further geared up the technology's moving into the
mainstream industry. Products, solutions, services, and applications are
continuously seen to spring out and evolve.
At the core of BPEL is a set of language constructs. For an XML-based
language, the specii cation gives syntactic dei nitions to the XML elements,
and explains how they should be used and structured to document valid
BPEL processes according to the semantics and the models established
behind. The key set of constructs is known as the “
activities.
” They abstract
the behavioral and structural capabilities of BPEL, dealing with service
interactions (e.g.,
invoke
,
receive
,
reply
), l ow control (e.g.,
if
,
while
,
repeatUntil
,
pick
,
sequence
,
l ow
,
foreach
), data manipulation (e.g.,
assign
), and fault
handling (e.g.,
throw
,
rethrow
). Others have to do with advanced scope
management (e.g.,
faultHandler
,
compensationHandler
,
eventHandler
), decla-
rations (e.g.,
variable
,
partnerLink
,
correlation
), and so on.
8.3
The primary use of BPEL is to model service interactions that comprise
distinct application behaviors. The hub-and-spokes orchestration model
has decided that the elementary interaction activity BPEL can describe is
Interaction Modeling
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