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3 Advanced Synchronization 117
techniques for reset nets is then proposed. The proposed semantics uphold the notion
that an OR-join waits to synchronize when necessary and continues when appropri-
ate. In addition, we have operationalized this formal semantics and presented an
efficient implementation in the workflow language YAWL using two optimization
techniques. To the best of our knowledge, no other semantics or workflow system
implementation come close to supporting such a general OR-join, especially in the
presence of potentially unbounded behavior and arbitrary cancelation regions.

Exercises

Exercise 1. Consider the set of reachable markings for the YAWL net in Fig. 3.1,
whereby the split behavior of task A is now an XOR-split. Describe at which
markings task E will be enabled.

Exercise 2. Construct a reachability graph for the YAWL net in Fig. 3.8 and indi-
cate at which markings the OR-joins will be enabled according to the proposed
OR-join semantics in this chapter.
Exercise 3. For the YAWL net in Fig. 3.9, please indicate at which of the following
markings the OR-joins will be enabled and why.
Markings c4, c6, c4 C c5, c4 C c6 for the OR-join E
Markings c3, c7, c1 C c3, c2 C c5, c3 C c5, c3 C c6, c3 C c7 for the OR-join F

c1 C c6

c4
A c2 B E
c5
c3 D c7

Fig. 3.8 A YAWL net with two OR-joins, C and E

c4 E c7
c1 C

A c5 D c6 F
c2 B c3

Fig. 3.9 A YAWL net with an OR-join task E preceding another OR-join task F