In our last post we considered Scheduling in the context of Planning; now, let’s explore how both Planning and Scheduling enable Execution, noting their respective roles and analyzing their interdependencies.
We plan/schedule to help us execute: to do the right things at the right times in the right ways to efficiently achieve an objective. But in a dynamic world we’re constantly adjusting plans/schedules to reflect reality, which begs a key question: What parts of a plan/schedule can we change without sacrificing productivity?
We want our plan/schedule to reflect reality as much as possible, but we also need sufficient plan stability to avoid generating waste, getting ready to perform one task and then doing something else. So, inside this lead time we don’t re-plan (except for major disruptions, when such waste is warranted), and work with older data. This first part of the plan belongs to Execution, defining a frozen period, a boundary enabling us to consistently re-align our plans with reality without sacrificing efficiency.
Planning/Scheduling workflows need an accurate picture of the conditions expected at the Execution boundary, at the end of the frozen period. Given this starting condition, re-planning/scheduling can align plans with Execution, closely reflecting reality without destabilizing our work environment. When Execution experiences a major disruption, requiring a relaxation of all or part of the frozen period to enable more complete re-planning, execution and planning/scheduling workflows and interfaces should be designed to provide this capability.
Though planners may request visibility to frozen plan details within planning/scheduling workflows, such detail is irrelevant for planning/scheduling purposes. Providing it can actually be problematic since planning/scheduling tools generally approximate reality, not fully considering execution-level detail. Execution may work the plan/schedule in ways that violate simplistic constraints and interdependencies inherent in the system-generated plan/schedule, making accurate representation in planning/scheduling systems very difficult or impossible, encumbering and possibly destabilizing planning/scheduling workflows.
Now that we’ve explored planning theory and analyzed the relationships and interdependencies between Planning, Scheduling and Execution, in our final post we’ll take a step back and look at the big picture to summarize what we’ve found and why it’s important.