Grid Services Orchestration with OMII-BPEL - Grid Computing: Infrastructure, Service, and Applications - page 194

a procedure P dei ned in a parallel for each statement modii es a variable
V in the outer scope S . When P is iterated in parallel, there are chances
that V will be modii ed at the same time. To avoid the situation, an isolated
scope IS can be inserted to for each and wraps up exactly where in P
variable V is modii ed, indicating a forced serialization of that access . The
BPEL engine is responsible for the actual implementation of serialization.
An isolated scope can be activated by setting the corresponding attribute in
a normal scope.

<bpws:scope isolated=”yes” name=”aScope”>
…
</bpws:scope>

8.5
The Web service framework is built on the foundation of XML supports.
XML schemas and documents ensure the consistency, interoperability,
integrity, and validity, as well as the l exibility of data sharing across
information systems. Inherently, XML suggests a strong typing system
for dei ning structure application data, which we i nd to be rather impor-
tant for grid computing. Typical grid applications produce a massive data
volume that is critical either as computational results on their own or as a
shared database across organizations. A weakly typed system does not give
enough coni dence on the validity of data, especially if the computation is
experimental or by any means capable of producing exceptional results in
unpredictable manners. Syntactic validation gives early opportunity to
expose apparent mistakes in data, and possibly to dei ne error-recovering
strategies in advance. Faulty data can be kept from further processing,
wasting more time and resources, or even putting systems in an unstable
state. For a complex system, especially one operating in a service-oriented
architecture in which services as distributed modules utterly reply on the
accuracy of application data received to participate in application logic, the
ambiguity of information must be avoided. The bottom line is, some forms
of validation will be required sooner or later to build a reliable application
system, if not systematically, then probably programmatically.
BPEL inevitably needs to deal with XML data. Service interaction is about
delivering service data in XML, either sending or receiving, so they must be
modeled in the BPEL process. BPEL needs to access these data as dei ned in
their WSDLs and schemas to extract, modify, compose, and validate appli-
cation information with i ne-grained details. Assign is a powerful activity of
BPEL designed for such purposes. Assign allows the encapsulation of single
or multiple copy s to specify how XML data can be assigned from a source to

Data Handling