The concept of a "solution plan" is used to characterize the structure of interactive systems in which the user guides the solution process. A formalism for describing and analyzing solution plan structures is presented. The formalism can be used to define the role of the user in an interactive system. The solution plan approach to interaction is particularly applicable to problems which have an obvious graphical representation. An interactive graphics system for solving a class of routing problems is described. Suggestions for the application of the approach to other problems are included
