Theory of Constraints Handbook - James Cox Iii [663]
A visual aid with explanations will be useful for further explaining the logic of how the PAs are written. Figure 34-4 shows a generic example with respect to sufficiency-based logic. Within the TP of TOC, we read sufficiency-based logic as follows: If A and B and C, then D is the unavoidable result. The oval shape represents a logical “and.”
FIGURE 34-4 Sufficiency-based logic example.
FIGURE 34-5 Logic within the PAs.
Figure 34-5 shows an example of how the PA is written. As stated earlier, the PA presents cause-and-effect logic, not a bullet list. If the logic were the same as presented in the previous generic example of sufficiency-based logic, then the PAs would appear as shown in Fig. 34-5. Often, we would verbalize D as starting with a word such as “Therefore, . . .” to indicate that it is an effect or a conclusion that results from the previous statements of A, B, and C.
Every tactic must get results and is written as an action. The tactics are written in the order in which they are implemented. Note: The logic explaining each tactic must be clearly presented in the PAs. We can write, “Vast experience shows that . . .” in a PA if it will be explained lower in the S&T tree. The tactics in Level 5 explain exactly what to do.
It is not possible to come up with an SA that proves the steps below are sufficient to achieve the step above them. The only real test is reality. The solution was to have the SA highlight a fact that, if not dealt with by steps of the corresponding lower level group of that step, would result in sufficiency not existing. The SA must be something that is common sense, but is typically ignored; that if ignored will not result in sufficiency. They are “Confucius says” statements, which are generic. A step has an SA only if there is another level of the S&T tree written below that step.
Figure 34-6 will be helpful for clarifying the logic. The SA is based on sufficiency-based logic, as described earlier. One way to read it is as follows: If Steps 2.1 and 2.2 are achieved, then Step 1 will be the unavoidable result because the SA of Step 1 was a fact of life (assuming reality verifies that sufficiency was actually achieved). Another way to read it is: If Step 2.1 and Step 2.2 are achieved and the SA of Level 1 is a fact of life, then Step 1 is the result.
When preparing to write the next level of the S&T tree, we think of the how (the titles) and the why of the steps and the sequence of the steps. The next level below a step must have a minimum of two steps for it; otherwise, the content should be within the step itself. When creating the steps, we do not artificially break the content into two parts, but rather divide it logically into two or more parts. When I was writing Level 5 of the Retailer S&T tree, I had to figure out how to write the steps in Level 5 below Step 4.11.2 of Keeping Correct Inventory levels. I realized the way to logically divide it in Level 5 was to have one step explaining Buffer Management (BM), the mechanism that automatically ensures correct inventory levels, and to have another step specifically focused on adjusting for peak demand, explaining how to adjust the mechanism for upcoming expected spikes in demand that are due to a sale or other planned or known event. Later, expediting was also added as a step.
FIGURE 34-6 Visual aid for SA connection.
It is much easier to write the SA for a step after we have completed writing the steps below that step in the S&T tree; then, we have enormous intuition. The SA does not have to address all the steps below it, but it is better if it does. It is especially important to address the first step (the one to the left) of the corresponding steps below. It is better to take a known phrase/quote and change it to what we need. It makes the SA verbalization more interesting. An NA and SA can be essentially the same.
Note: We decided not to have sequence assumptions in the S&T tree. Therefore, we have to