Re: [wsbpel-comment] Isolated scope semantics

[Dieter Koenig1 <dieterkoenig@de.ibm.com>]

Hello Artem, the semantics of isolated scopes w.r.t. concurrent access to
variables follows the serializability semantics for concurrent transaction
executions.

However, the language in the WS-BPEL 2.0 standard, section 12.8.:
   "Suppose two concurrent isolated scopes, S1 and S2, access a common set
   of variables and partner links (external to them) for read or write
   operations. The semantics of isolated scopes ensure that the results
   would be no different if all conflicting activities (read/write and
   write/write activities) on all shared variables and partner links were
   conceptually reordered so that either all such activities within S1 are
   completed before any in S2 or vice versa.
   (...)
   The actual mechanisms used to ensure this are implementation dependent."
leaves it to the implementation whether it completely serializes the
execution of isolated scopes concurrently accessing variables or allows
some degree of overlapping execution.

Typically, overlapping execution of isolated scopes can be allowed up to
the point of the first access to a concurrently accessed variable, without
any limitation w.r.t. their contained control flow. This is different from
the Interleaved Parallel Routing pattern where "no two activities from the
set of activities subject to interleaved parallel routing may be executed
at the same time".

HTH
Kind Regards
DK
                                                                       
 Dieter König                          Mail: dieterkoenig@de.ibm.com         IBM Deutschland Entwicklung GmbH
                                                                       
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  From:       "Artem Polyvyanyy" <artem.polyvyanyy@hpi.uni-potsdam.de> 
                                                                       
  To:         <wsbpel-comment@lists.oasis-open.org>                    
                                                                       
  Date:       10.12.2007 14:15                                         
                                                                       
  Subject:    [wsbpel-comment] Isolated scope semantics                
                                                                       





Hello,

I want to clarify the semantics of the Isolated Scope as defined in "Web
Services Business Process Execution Language Version 2.0" specification.

Let's define a use case as a process with two concurrent isolated scopes
that work on a shared set of variables. What is the correct semantics of
such process?

a) 2 isolated scopes are seen as database serialization transactions.
Once you enter each scope you work with the snapshot of variable values
you observed. So commits in one scope will be not seen in the second
scope;
b) Within one (or) both scopes all the activities are done sequentially
(no parallelism allowed);
c) Not depending on which order you will execute activities from one (or
both) scope(s) the end results on variables will be the same ??!!
d) Another one.

I ask because what I read and what I discuss with people varies. I am
particularly interested in isolated scopes application for modeling
interleaved parallel routing workflow pattern and it's relation to the
fact that isolated scope might contain control flow.

Best regards,
Artem


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