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2 The Language: Rationale and Fundamentals 97
Retain familiar and four eyes constraints are specified between the following
tasks when distributing work:
– Update Shipping Purchase Order and Issue Shipment Purchase Order (retain
familiar)
– Arrange Delivery Appointment (SP) and Arrange Pickup Appointment (SP)
(retain familiar)
– Arrange Delivery Appointment (FTL) and Arrange Pickup Appointment (FTL)
(four eyes)

2.9 Conclusion

In this chapter, we have introduced the YAWL language in both conceptual and oper-
ational terms, describing its major features in the control-flow, data, and resource
perspectives. The derivation of these language features from the Workflow Patterns
is described in detail as are the formal modeling foundations on which YAWL is
based. In doing so, we trust that we have laid the groundwork for the reader to
tackle subsequent chapters of this book that assume some knowledge of the material
discussed in this section.

Exercises

Exercise 1. Identify the main YAWL split and join operators. Model each of these
in terms of Petri nets.

Exercise 2. Model the following process as a Petri net and then as a YAWL model.
Highlight the differences between the two models.
A travel agency makes travel arrangements for people
A travel arrangement may include one or more of the following activities: book
flight, book car, and book hotel
These activities occur in parallel
As they involve dealing with third parties, each of the booking activities may be
either successful or unsuccessful
When all booking activities requested by a customer have completed success-
fully, the payment activity is triggered
If any of the booking activities are unsuccessful, any further progress on the
booking activities (if any) is canceled
The process completes after either a payment or cancelation activity

Exercise 3. Model the following process as a Petri net and then as a YAWL model.
Highlight the differences between the two models. Identify the patterns that exist in
each model.