The Prerequisite Tree (PRT) Domain

Why using Prerequisite Trees (PRTs)? 

PRTs are a planning tool to achieve a known goal/objective. It is basically a break down on the steps in order to get you were you want to be.  Each step is based on an identified “Obstacle” that you will overcome by a “state” which is again nothing else as an (intermediate) objective.

PRTs are useful because of their simplicity and because they embody a simple principle from Stephen Cowley: “Start with the End in Mind” . 

PRT Domain Description

The diagram below describes the domain. One starts with the Objective, and uses necessary condition thinking to define all known immediate obstacles that one sees from achieving that particular objective. Then for each obstacle one considers the intermediate objectives that would help you to overcome the obstacle. Then you consider what obstacles are keeping you from achieving each of the intermediate objectives. And so forth, until each step from now to the Objective is identified. 

The PRT Domain
Node Type Description Is Starting Point / Successors
Objective The Objective that you really care about Yes / –
Obstacle One of potentially many obstacles that you need to overcome to meet an Objective No / Objective, Intermediate Objective, (OR)
Intermediate Objective An objective that if achieved will overcome the following Obstacle No / Obstacle (OR)
OR  As a necessary condition all incoming arrows normally mean that all are necessary. You can change this with an OR  No / all other Nodes Types

Background Information on CRT Domain

CRT diagrams were developed as part of the Theory of Constraints by E. Goldratt. More on Theory of Constraints can be found here