The execution behavior of a CTN provides an interpretation
of the collaborators’ experiences when interacting under the
control of a CPS. As in the original Trellis model, a token in
a place p indicates that the contents of the place Cl(p) are
displayed for viewing (or editing, or some other interaction).
Content elements come into and go out of view (or begin and
end execution) as tokens move through the net. Transitions
are fired by selecting logical hypertext buttons. When a
transition t is fireable in the timed Petri net, its logical button
Bl(t) is displayed in some selectable area of the screen, such
as on a (highlighted) word in a text section, or in a separate
The general execution behavior of the CTN in a CPS requires
pattern matching to be done on all arc expressions that are
inputs to a transition. The transition is enabled if there is one
or more consistent color substitutions for the expressions.
When the transition fires, one of the valid substitutions is
chosen, the proper color tokens are removed from the input
places, and output tokens are produced according to the
substitution and the expressions on the output arcs.