The nonlinear nature of plans

We usually think of plans as linear sequences of actions. This is because plans are usually executed one step at a time. But plans themselves are not constrained by limitations of linearity. This paper describes a new information structure, called the procedural net, that represents a plan as a partial ordering of actions with respec to time. By avoiding premature commitments to a particular order for achieving subgoals, a problem-solving system using this representation can deal easily and directly with problems that are otherwise very difficult to solve.