xoEPC - Jan Mendling

78 3. Event-driven Process Chains (EPC)
d
d d
c3
d
e1 f1
f2 e2
d
c4
d
w
c2
c5
s1
c1
w
e3
w
w
c6
w w
Figure 3.18: A structured EPC with a negative token on the negative upper corona of
OR-join c5
since a node can fire only if all its outputs are empty. Due to the safeness property, we
already know that the state space is finite since also the number of arcs is finite for an
EPC. Another observation is that there are several state and context propagations that
are not interesting to the user of the model. Therefore, the following section will make
a distinction between the transition relation of an EPC that covers all state and context
changes, and the reachability graph that only covers the propagation of positive tokens
and hides context and negative token propagation.
This semantics definition based on state and context implies that the examples of
Section 3.4 behave as follows.
• Figure 3.6(a): The single OR-join on the loop produces a wait context at a9. There-
fore, it is blocked.
• Figure 3.6(b): The two OR-joins produce a wait context at a23 and a24. Therefore,
they are both blocked.