Constraint in the Work Flow, Work Process and Work Execution

Thomas “Tom” Cagley Jr., the host of the Software Process and Measurement Cast, published his weekly Re-Read Saturday covering Chapters 9 of my Tame your Work Flow book.

Tom elaborated on discovering the Constraint in the Work Flow and the Constraint in the Work Process.

The difference between the two is not an intuitive one, as Tom himself says:

“[…] the distinction between constraints in the work process and workflow initially felt academic. It was not until my second reading of this chapter during an early review that the understanding that knowing the two types of constraints can occur in different parts of a delivery process and that how you exploit and then evaluate each type of constraint can be very different.”

Revisiting the Jungle, Jeep and Journey Metaphor

Indeed, reflecting on Tom’s statement above, acquiring the Mental Model exemplified by the metaphor of the Jungle, Jeep and Journey metaphor is one of the most powerful and most difficult things to master when learning how to manage Operational Flow with the TameFlow Approach.

Note: If you are not familiar with the Jungle, Jeep and Journey metaphor, checkout the Campfire Talks with Herbie (#3) and Minton Brooks for an introduction.

The complication comes from the fact that practitioners will tend to try to classify where the constraint is in isolation, in a static manner. Another kind of very common error is to think of these as three different kinds of Constraints. In reality, we need to consider the Work Flow, the Work Process and the Work Execution as one of three possible locations of the Constraint - but in relation to the perspective we are holding during the inquiry. Here is a summary of how it works:

  1. The Constraint in the Work Flow is what you will typically use during the Full Kitting activity. It is forward looking. It is where you expect the Constraint to be in the future, when the Work being planned will be released into the Work Flow.
  2. The Constraint in the Work Execution is where you detect, dynamically and in the present while that the Work is flowing through the Work Flow, that there is a potentially disrupting slowdown, that could become a temporary Constraint (for the time being) or the new Constraint in the Work Flow.
  3. The Constraint in the Work Process is the Work Process stage with the longest average Flow Time. In practical terms: it is the column on the Flow Efficiency Board of the “Herbie” team that has the longest average Flow Time. It is this team’s board that needs to be instrumented (at least) as a DBR Board (or better yet as a TameFlow Board) in order to provide the Replenishment Signal to release new Work into the Work Flow and thus Limit WIP.

Note that when the Work Execution Signals (stemming from the MOVE Buffers of the teams) indicate that some team is potentially becoming the new “Herbie” team, then the best way to handle the situation is to activate its DBR Board.

Then you monitor concurrently both the “old” Herbie team and this new “candidate” Herbie team. The one that has the most unfavorable DBR Buffer will raise the Replenishment Signal (for the time being).

When the temporary hiccup is resolved, it is time to draw conclusions - typically in the retrospective at the end of the delivery of the current MOVE. This is the backward looking perspective; where we tend to learning.

The most likely scenario is that the hiccup was due to some Special Cause Variation. If so, things return to “Business as Usual” - meaning that the old “Herbie” team, still remains the “Herbie” team.

If after the resolution, the new candidate “Herbie” team remains the most challenged, we have witnessed a change due to Common Cause Variation.

This must be confirmed though.

The confirmation will come during the upcoming Full Kitting activities. If the “Herbie” team has truly moved, then the Virtual Queue in front of it - as established during the planning phase - will be the longest. That team will be confirmed as the new Constraint in the Work Flow - and the cycles starts over again. It is that team’s Herbie column that will be used in the selection and prioritization of new work with the Financial Throughput we compute there.

One subtlety here is that during the Full Kitting activity one should not consider the team with the longest average in-state Flow Time in absolute terms. One must make the decision based on the Virtual Queues. In fact one team might be very “slow”, but also have very little to do. A “faster” team facing a ton of incoming Work Load is more likely to be the Herbie team. That’s why during the planning phase we try to figure out where those queues will be - and that’s where the speed of automated forecasting based on Flow Metrics becomes invaluable; and avoids wasting time in expert-opinion estimation by the engineering teams. (The business side can spend time in expert opinion estimation of value anyway, because typically they have much more time on their hand than the engineering side.)

In conclusion, mastering how the Jungle, Jeep and Journey all interact - from planning, to execution, to retrospective - is an absolutely critical skill to develop in order to properly manage the Operational Flow and do so while actually thinking in terms of Constraints Management.

Addressing the Dancing Constraint

As explained in the Tame your Work Flow book, one of the greatest challenges when trying to perform Step 1: Identify the Constraint of the Five Focusing Steps, is that in knowledge-work, the constraint appears to be moving around all the time. The situation is rendered even worse when using process crutches as Column WIP Limits. In short: there is no way to distinguish the real signal from the noise. In fact, there will be a cacophony of signals, which make it impossible to detect the Constraint.

With the Jungle, Jeep and Journey metaphor we have a way to focus our investigation. The relative Buffer Consumption of all teams involved will quickly allow us to zoom in onto the team that is problematic. But we don’t react in panic, proclaiming that that team is the new Constraint. We will accept that a Constraint has moved only when we see clear evidence - like the longer queues and the measured in-state average flow times - that it really has moved.

The Jungle, Jeep and Journey metaphor is a great filter: it allows us to ignore all noise, and only focus on the true signals - thus providing us the means of performing the critical Step 1: Identify the Constraint.