Tame your Work Flow
Today, we re-read chapter 12 titled Drum-Buffer-Rope (DBR). The concept of DBR is critical to using the Theory of Constraints in real-world environments. There are a couple of important premises that DBR scheduling is built upon that bear remarking on before we dive into the nuances of chapter 12 of Tame Your Work Flow. The first is that you need to know where your constraint is at all times. This means that someone needs to pay attention to the flow and pace of work. This infers a degree of discipline that can be problematic. As we have noted the constraint can move based on the kind of work in the pipeline and where we are in the cycle of finding, exploiting, and improving the constraint. While this might sound onerous, in order to maximize the flow of value through a value stream or value network it is imperative. The second is the discipline of the queue. DBR has an expectation that if there is more than one project or piece of work and product owner, jumping the turnstile is not acceptable behavior. In other words, work is done in the agreed-on order based on priority the organization agrees on upfront. The discipline of the queue is often a problem because of individual incentives.
I was trained from toddlerhood that idle hands were the playground of the devil. Being busy was the right answer for pretty much everything. Common management practices over the years reinforced that bias, which is when I was first introduced to DBR it was hard to grasp, the goal was to maximize the utilization of each person. In most moderately interesting knowledge work processes the constraint is not the first step in the processes. DBR establishes a buffer just in front of the constraint so that the constraint is always busy. I am good to this point – busy is good (in proper terms this is called exploiting the constraint). When work is pulled from the buffer it needs to be replenished therefore the next piece of work is pulled in creating a ripple effect through the process up to the point of pulling work from the committed backlog. All is good until you consider the steps that aren’t the constraint. Unless you have constructed a perfectly balanced system, steps that are not the constraint will not always be busy. Doing work that won’t be immediately used increases the likelihood of defects and other technical debt. The process needs to work to the pace of the constraint (drum). Once I understood the DBR idea, the agile concept of swarming made A LOT more sense and caused me to have a renewed focus on flow and process improvement.
Steve and Daniel, spend a lot of time in the chapter discussing the negative aspects of using WIP limits. Suffice it to say that in complex scenarios (PEST) unless someone is focused on monitoring the constraint and that product owners (and everyone else that can command people) respect the queue WIP limits are required. However, WIP limits can cause distortions, hide the constraint, and cause excess WIP across the overall value stream as everyone maximizes their own flow (they like to be busy too). Quoting the authors, “Focus on emptying the queues, not on keeping the (Non-Constraint) workers busy!”
The idea of focusing on overall flow means that organizations need to spend the time and effort on understanding their value chains and value networks. This is not a trivial effort but unless you know the full path required for work to go from concept-to-cash it is very easy to spend your limited process improvement budget on work that leads to local optimization rather than top-line or bottom-line impacts.
Remember to buy a copy of Tame your Work Flow to support the authors and blog!
Week 1: Logistics and Front Matter – https://bit.ly/2LWJ3EY
Week 2: Prologue (The Story of Herbie) – https://bit.ly/3h4zmTi
Week 3: Explicit Mental Models – https://bit.ly/2UJUZyN
Week 4: Flow Efficiency, Little’s Law and Economic Impact – https://bit.ly/2VrIhoL
Week 5: Flawed Mental Models – https://bit.ly/3eqj70m
Week 6: Where To Focus Improvement Efforts – https://bit.ly/2DTvOUN
Week 7: Introduction to Throughput Accounting and Culture – https://bit.ly/2DbhfLT
Week 8: Accounting F(r)iction and Show Me the Money – https://bit.ly/2XmDuWu
Week 9: Constraints in the Work Flow and in the Work Process – https://bit.ly/33Uukoz
Week 10: Understanding PEST Environments and Finding the Constraint in PEST Environments – https://bit.ly/3ga3ew9
Software Process and Measurement 
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