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56 N. Russell and A. ter Hofstede

check account decline order return
stock
take order credit

check
pack order despatch
Fig. 2.17 Workflow net example: order Fulfillment process

place transition arc reset arc

Fig. 2.18 Reset net constructs

(a) (c)

(d)
(b)

Fig. 2.19 Reset net operational semantics

significant omission, given the relative frequency of cancelation in real-life pro-
cesses.

2.3.3 Reset Nets

The inability of standard Petri nets and workflow nets to directly capture the notion
of cancelation within a business process spurred the use of reset nets for this pur-
pose. Reset nets are able to explicitly depict notions of cancelation within a process
definition.
In Fig. 2.18, it can be seen that reset nets are made up essentially of the same
constructs as standard Petri nets with the addition of a reset arc. Like normal input
arcs, reset arcs connect places to transitions; however, they operate in a differ-
ent way. When the transition to which a reset arc is connected fires, any places
connected to the transition by reset arcs are emptied of any tokens that they may con-
tain. Figure 2.19a–d illustrate various scenarios of reset net operation. Note that the
tokens in places attached to a transition by reset arcs play no part in the enablement
of the transition.
As with other Petri net-based modeling formalisms for business processes, one
of the advantages offered by reset nets is that they can be defined in a formal way.