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3 Advanced Synchronization 119
Chapter Notes

The formal semantics defined in this chapter represent a second attempt at defin-
ing the OR-join semantics in YAWL. The original semantics of the OR-join in
YAWL can be found in this paper [15]. The original semantics have been found
to be problematic when there are multiple OR-joins in the net at the same level and
in composite tasks. The reasoning behind the current OR-join semantics together
with the formal foundations of the approach can be found in the PhD thesis of the
first author [272]. The work on the current OR-join semantics was first published in
2005 [273] and the extended version with technical details of the restriction tech-
niques and empirical evidence of their improved performance using several YAWL
nets can be found in [275].
An OR-join formalization is proposed for syntactically correct EPCs based on the
notion of state (i.e., marking of tokens) and the context (i.e., wait or dead status of
an arc) in [162]. The context of an input arc to an OR-join is then used to determine
whether an OR-join should be enabled at a given state. The semantics proposed by
Mendling, however, will mean that if there is a deadlock preceding an OR-join (e.g.,
a situation where an AND-join connector upstream cannot propagate tokens due to
a deadlock), the OR-join connector downstream will continue to wait for a token.
Additional details can be found in Mendling’s PhD thesis [160].
The issue of “vicious circles” in EPCs is pointed out in [9]. The proposal by
Kindler for a nonlocal semantics of the OR-join in EPCs can be found in [132,133].
More information on IBM Websphere MQ Workflow can be found in [150]. The
Eastman manual that was referred to in this chapter is [85].
The definition of the OR-join by the Workflow Management Coalition is taken
from [270].
The reader is referred to [261] for further information about BPMN and to [263]
for a discussion on why BPMN’s inclusive OR-join gateway does not work correctly
in the context of unstructured models. The specification of BPMN 1.0 by the OMG
is described in [185]. More on the relationship between BPMN and YAWL can be
found in Chap. 13.