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13 The Business Process Modeling Notation 355
Ordering
Order not
approved
Approve Confirm
Create Purchase
Purchase Order Order Purchase
Order approved Order
Modify
Purchase
Order

Order not Order
approved timed out
Fig. 13.6 Example of a business process model with exceptions

Figure 13.6 shows a BPMN model that contains exceptions. After the approve
purchase order, there is a choice not to approve the order. When this choice is made,
an error event order not approved is generated, upon which the subprocess contin-
ues along the flow that leaves the corresponding error exception event. The error
event triggers the order not approved error intermediate event that is attached to
the subprocess activity, which leads to the completion of the main process (via the
XOR-join gateway). Similarly, the main process completes upon the occurrence of
the order timed out timer exception event.

13.3 Mapping BPMN to YAWL

This section shows how the BPMN concepts and constructs introduced in the previ-
ous section can be mapped into YAWL. We first discuss the mapping of control-flow
aspects before moving into the data and the resource perspective.

13.3.1 Control-Flow

At their core, BPMN and YAWL share many common concepts. For example, the
concept of task in BPMN matches the concept of task in YAWL, the concept of
gateway in BPMN matches the concept of decorator in YAWL, and the concept of
flow in BPMN matches the same concept in YAWL.
For illustration, Fig. 13.7 shows side-by-side the BPMN diagram previously
shown in Fig. 13.1 and the corresponding YAWL net. Note that this YAWL net
differs slightly from the Freight In Transit YAWL net shown in other chapters.
Specifically, the decision on whether to issue more trackpoints or not is captured
using an XOR-split decorator rather than using an explicit condition. This slight