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