Java Reference
In-Depth Information
will be working full time. Or perhaps the payroll system takes some length of time to com-
plete an internal operation, so instead of sitting around waiting for it to finish, you'd like to
have certain parts of the process execute concurrently.
Such a business process that defines a new service by reusing existing services in a compos-
ition would require an environment of its own in which to execute. Of course, you could just
write some procedural Java code to perform each step in your process, but you'd like to ex-
pose the process itself as a service.
BPEL (commonly pronounced “BEE-pell” or “bipple”) provides the orchestration layer with-
in a SOA. Orchestrations define the business process around which services will be invoked.
A deployed BPEL application represents a new, complex composite service that is composed
of basic services. A BPEL is an XML document, with a .bpelextension, that conforms to the
WS-BPEL standard and executes in its own environment, a BPEL engine.
Benefits of BPEL
There are several benefits to using BPEL as a central component within a SOA:
▪ It's an industry standard. BPEL was originally released as a specification in July of 2002
in a joint effort by BEA, Microsoft, and IBM. More recent versions of the spec contain
contributions from SAP and Siebel Systems. Since its original release, it has undergone
revision and close scrutiny, and was eventually released to OASIS Open for maintenance
by a technical committee as an open standard. Therefore, you can implement BPEL pro-
cesses without fear of vendor lock-in, and without worrying that you are basing your work
on an untested fad that only operates in a tiny corner of the IT universe.
▪ It's designed as part of the web services stack. While you aren't limited to using SOAP
messages in your orchestrations, it does use WSDL, and you can leverage SOAP, WS-Ad-
dressing, security, and other integral aspects of the WS-* specifications.
▪ It's purely XML, so it's portable across platforms and vendors. It relies on XML schema
for its data model, and BPEL documents are human-readable and can be processed and
transformed with any XML tools.
▪ It abstracts business logic, and acts as a reusable container for service compositions. Be-
cause processes are exposed as WSDLs, sophisticated orchestrations may invoke other or-
chestrations along with other individual service implementations. Because the flow direct-
ives are abstracted up to a BPEL, your service implementations are free to remain highly
cohesive.
