Page 250 -

244 M. Adams

Fig. 9.2 YAWL Engine internal architecture

The Net Runner is responsible for progressing a process instance in terms of its
control-flow, and is arguably the most critical Engine component. A net runner is
created for the root net and each subnet (if any) of a process instance as required,
and so a case may have a number of net runners associated with it at any one time,
each responsible for exactly one net. Conceptually, a net runner traverses the net
from start condition to end condition, enabling tasks along the path determined by
the net’s control-flow. At each progress iteration (i.e., when the net begins and after
each task reaches a completion status), a net runner examines the current state of its