Example 14: Prerequisite Tree (PRT)

A planning graph showing obstacles blocking objectives and intermediate objectives to overcome them:

vgraph projectLaunch: PRT "New Product Launch Planning" {
    // The main objective we want to achieve
    node obj1: Objective "Successfully launch product by Q3";

    // Obstacles blocking the main objective
    node obs1: Obstacle "Development team lacks required skills";
    node obs2: Obstacle "Marketing budget not approved";
    node obs3: Obstacle "No distribution channel established";

    // Intermediate objectives to overcome obstacles
    node io1: IntermediateObjective "Train team on new technology";
    node io2: IntermediateObjective "Hire experienced developers";
    node io3: IntermediateObjective "Present ROI analysis to leadership";
    node io4: IntermediateObjective "Partner with existing retailer";
    node io5: IntermediateObjective "Build direct-to-consumer channel";

    // OR junctor for alternative paths
    node or1: OR;
    node or2: OR;

    // Further obstacles blocking intermediate objectives
    node obs4: Obstacle "Training budget limited";
    node obs5: Obstacle "Talent pool is competitive";

    // Obstacles block the main objective
    edge obs1 -> obj1: obstacle_blocks_objective;
    edge obs2 -> obj1: obstacle_blocks_objective;
    edge obs3 -> obj1: obstacle_blocks_objective;

    // Alternative ways to overcome skill obstacle (via OR)
    edge io1 -> or1: intermediate_objective_to_or;
    edge io2 -> or1: intermediate_objective_to_or;
    edge or1 -> obs1: or_to_obstacle;

    // ROI analysis overcomes budget obstacle
    edge io3 -> obs2: intermediate_objective_overcomes_obstacle;

    // Alternative distribution solutions
    edge io4 -> or2: intermediate_objective_to_or;
    edge io5 -> or2: intermediate_objective_to_or;
    edge or2 -> obs3: or_to_obstacle;

    // Recursive obstacles blocking intermediate objectives
    edge obs4 -> io1: obstacle_blocks_intermediate_objective;
    edge obs5 -> io2: obstacle_blocks_intermediate_objective;
}

Note: PRT graphs flow bottom-to-top like other TOC tools. The main Objective sits at the top, with Obstacles directly below showing what blocks it. IntermediateObjectives below the obstacles show what needs to be achieved to overcome them. The OR junctor indicates alternative paths - only one of the connected intermediate objectives needs to be achieved. PRT embodies "necessary condition thinking" - working backward from the goal to identify all prerequisites.