4.1. Conceptual Modeling of Processing Networks

For accommodating PN modeling, OEM-A is extended by adding pre-defined types for processing objects, entry node objects, arrival events, processing node objects, processing activities, exit objects and departure events, resulting in OEM-PN. These "built-in" types, which are described in Figure 4-2, allow making PN models based on them simply by making a process model (with DPMN) without the need of making an information/class model as its foundation, as shown in Figure 4-3.

Figure 4-2. A conceptual OEM class model defining built-in types for conceptual PN modeling
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An example of a conceptual PN model: Department of Motor Vehicles

As a simple example of a PN simulation model we consider a Department of Motor Vehicles (DMV) with two consecutive service desks: a reception desk and a case handling desk. When a customer arrives at the DMV, she first has to queue up at the reception desk where data for her case is recorded. The customer then goes to the waiting area and waits for being called by the case handling desk where her case will be processed. After completing the case handling, the customer leaves the DMV via the exit.

Customer arrivals are modeled with an «entry node» element (with name “DMV entry”), the two consecutive service desks are modeled with two «processing node» elements, and the departure of customers is modeled with an «exit node» element (with name “DMV exit”).

DPMN is extended by adding the new modeling elements of PN Node rectangles, representing node objects, and PN Object Flow arrows, representing combined object-event flows. PN Node rectangles take the form of stereotyped UML object rectangles, while PN Object Flow arrows have a special arrow head consisting of a circle and three bars, as shown in Figure 4-3.

Figure 4-3. A PN model using the new DPMN modeling elements of PN Node rectangles and PN Flow arrows
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Using both Object Flow arrows and Event Scheduling arrows

While an Object Flow arrow between two nodes implies both a flow of the processing object to the successor node and the resource-dependent scheduling of the next processing activity, an Event Scheduling arrow from a processing node to an Event circle represents an event flow where a processing activity end event causes/schedules another event, as illustrated in the example of Figure 4-4.

Figure 4-4. A DPMN-PN process diagram with an Event Scheduling arrow
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