Model where the discrete values of variables (also called levels) is determined by logical combinations of the values of other variables.

Logical model in which variables can take more than two levels.

Directed bipartite graph, in which the nodes represent transitions (i.e. events that may occur, signified by bars) and places (i.e. conditions, signified by circles). The directed arcs describe which places are pre- and/or postconditions for which transitions (signified by arrows) occurs.