This version of the net does not support the notion of time. Also, the noting of data types or token types is also missing. Clearly, some extensions are needed in order to make Petri nets practical for business process simulation. The key elements missing from the simplest form of the Petri net are conceptually simple, but add complexity when used in combination. This includes preemption whereby one transition may preempt another if the first has a higher, preemptive priority.
Transitions require more than just a marking to execute.
Aggregate multiple behaviors that are possible in a single transition. Transition behaviors spanning a spectrum of possibilities, each with its own chance of occurring. A big problem facing the analyst who is attempting to use Petri net technology is deciding just how to obtain objects which will populate the network. Most of today's methods can provide a partial list of objects and their properties as a complement to simulation techniques. Most BPR tools focus on traditional techniques such as relationships and definitions, while Petri nets elaborate the details of operation.