Thus far in our series on TOC’s Thinking Processes we have covered the Current Reality Tree, the Conflict Resolution Diagram and the Future Reality Tree. One of the subjects I have covered in the past, are the three very important questions that need to be answered before, during and after a continuous improvement initiative which are:
- What to change?
- What to change to?
- How to cause the change to happen?
The Current Reality Tree is used to answer the first question of "what to change?". The Conflict Resolution Diagram and the Future Reality Tree are intended to answer the question, "what to change to?". In this post we will cover the remaining two TP tools, the Prerequisite Tree (PRT) and the Transition Tree (TT), which are both used to answer the third question, "how to cause the change to happen?".
Before continuing on, I want to state that because of the complex nature of the PRT and the current belief that the usefulness of the TT has really proven to be limited, the amount of time we spend on these tools will be limited. We will discuss both of these logic trees, but we won’t delve into either one of them deeply. The reason for this is because in upcoming blog posts I will be introducing you to another tool referred to as a Goal Tree (a.k.a. Intermediate Objectives Map). The Goal Tree is a tool that very much simplifies your ability to improve your processes and systems. So with this in mind, let’s now move on to a brief discussion of the Prerequisite Tree and the Transition Tree.
The Prerequisite Tree
The Prerequisite Tree (PRT) is a logic structure designed to identify obstacles that get in the way of reaching your company’s primary goal. It identifies those necessary conditions that must be in place for goal achievement or some other desired outcome. As Dettmer  says, “The PRT is intended to lay out the components of complex execution for the realization of some desired outcome. Your objective, what you want to achieve, might only be one step in the solution of a much larger problem.”
The PRT uses the same necessity based logic as the Conflict Resolution Diagram which uses the syntax, “In order to have x, I must have y.” Dettmer uses the example of building a house, in that you need significant quantities of cement, lumber, steel and a place to build. He explains that without these items, you can’t even begin the actual work of construction. That is the concept of necessity, completing tasks or activities that must be done before another task can be started and ultimately before some outcome is achieved. In the figure below, Dettmer demonstrates the concept of necessity based logic.
What he is attempting to demonstrate, is there are tasks that must be completed before an upper level task can be undertaken. That is the essence of the PRT, meaning that these are the obstacles that stand in the way of completing the task of commencing the construction of a home. If obstacles do surface, and they typically will, Intermediate Objectives are then required to neutralize them.
The PRT contains the following parts when it is constructed:
- The Objective signifies the final outcome of all activities leading to it.
- Intermediate Objectives (IO) which are the activities that must be completed in order to achieve the objective.
- Obstacles which stand in the way of progress toward the objective.
- Necessary Condition Arrows are the arrows connecting the IO’s arranged from bottom to top. The direction of the arrows indicates the direction of flow or sequence in which the IO’s must be completed.
The Transition Tree (TT) has been shown to be not very popular among those learning the Thinking Process tools because it is difficult to create and use. Dettmer  explains that in teaching the TP’s, he observed that most students (and clients) had no patience for creating detailed TT’s. What usually occurred was that the students added too much detail. Dettmer eventually stopped using the TT because there were other tools that were far superior to it. As you will see, in the next series of posts, I have developed a way to use a different tree referred to as the Goal Tree. Dettmer is both the creator and proponent of this tool.
In my next posting I will introduce you to the Goal Tree and I’ll explain why I believe it is perhaps one of the best tools ever developed for achieving excellence in your company. As always, if you have any questions or comments about any of my posts, leave me a message and I will respond.
Until next time.
 The Logical Thinking Process – H. William Dettmer, Quality Press, 2007
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