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Today we tackle Chapter 8 of  Daniel S. Vacanti’s Actionable  Actionable Agile Metrics for Predictability: An Introduction (buy a copy today).  The chapter is titled, “Conservation of Flow Part II.”  In this chapter, we dive even deeper into the conversation of flow and why the assumption that work that enters a process completes and exits is important.

Vacanti begins chapter 8 with a reminder that Little’s Law, Assumption Two is that work, once started, will eventually be completed and exit the system. (Chapter 7 focused on assumption one, that the average entry and output would be the same).  Assumption two is a requirement for pull-based systems to work.

Pull systems, like Kanban, bring work into a process when there is capacity for the work to be addressed, completed, leave the system.  Pull systems allow for just-in-time prioritization.  Every time work is “pulled” into the system, there is an opportunity to decide which piece of work should be addressed next.  Vacanti suggests that “grooming, pruning, and re-prioritization” of backlogs is a waste of time. There is no reason to prioritize things if you are not sure they will ever be worked on.

The ready column introduced in Chapter 7 is a useful gate or limiter.  When work is drawn into the active part of the process it is withdrawn from the ready column, indicating that is time to replenish the ready column (up to the WIP limit set when the process is analyzed and the Kanban board is established).  As work is drawn into the ready column re-prioritization occurs.

Pulling work into the ready column is not only prioritization; it also reflects commitment.  Remember, that ready is part of the process (ready is post backlog) and assumption two holds that work that enters will eventually complete and exit.  Therefore just-in-time prioritization is the same as just-in-time commitment.  

Vacanti reminds us that work on the backlog does not reflect a commitment.

The distinction between the ready column and the backlog is important.  Backlogs are unbound and can be added to at will (and often by anyone).  The ready column is bound by a specific WIP limit and sends a clear message that work will be completed.

The concept of commitment means that the team will do everything in its power to ensure that any item that enters the process completes and exits. As many of us know, meeting commitments is important and not always easy.  Commitment also means that the team has the responsibility to communicate the cycle time probability range (the answer to the question, “when will it be done?”) for any committed item.

Vacanti concludes the chapter by tackling exceptions to the conservation of flow and the concept of conditioning flow and predictability. Even though our assumption is the everything that enter will exit, we all are aware that the assumption is a simplification of real life.  Sometimes things have to be abandoned.  When that occurs we need to capture the data and ask the question, how could this exception have been avoided.  The author states that exceptions are an opportunity to learn.

Conditioning flow and predictability deal with the realization that all people are not perfectly fungible and sometimes priorities need to be adjusted to deal with the realities teams face. When work is pulled out of priority order, the team needs to communicate the change and the impact on the cycle time range that they have communicated.  Conditioning flow is a reflection of the facts that we have control over the decisions we make and that the context we operate within is important.

Previous Installments

Introduction and Game Plan

Week 2: Flow, Flow Metrics, and Predictability

Week 3: The Basics of Flow Metrics

Week 4: An Introduction to Little’s Law

Week 5: Introduction to CFDs

Week 6: Workflow Metrics and CFDs

Week 7: Flow Metrics and CFSs

Week 8: Conservation of Flow, Part I

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