The history of task boards is an interesting study in idea diffusion. For Agile teams, they were modeled after the so-called Kanban (Japanese for “signboard”) that Taiichi Ohno of Toyota had pioneered for just-in-time manufacturing. Ohno created his own model after observing how American supermarkets stocked their shelves in the 1950s.11 Ohno observed that supermarket shelves were stocked not by store employees, but by distributors, and that the card at the back of the cans of soup, for example, was the signal to put more soup on the shelf. Ohno introduced this to the factory, where the card became the signal for the component supplier to bring a new bin of parts.
Surprisingly, only in the past few years have software teams discovered the value of the visual and tactile metaphor of the task board. And Toyota only recently looked to bring Agile methods into its software practices, based not on its manufacturing but on its observation again of Western work practices.12 So, we’ve seen an idea move from American supermarkets to Japanese factories to American software teams back to Japanese software teams, over a period of 50 years.
In software practices, Kanban has become the name of more than the task board; it is also the name of an alternative process, most closely associated with David J. Anderson, who has been its primary proponent.13 Where Scrum uses the team’s commitments for the sprint to regulate capacity, Kanban uses work-in-progress (WIP) limits. Kanban models workflow more deterministically with finer state transitions on PBIs, such as Analysis Ready, Dev Ready, Test Ready, Release Ready, and so on. The PBIs in each such state are treated as a queue, and each queue is governed by a WIP limit. When a queue is above the WIP limit, no more work may be pulled from earlier states, and when it falls below, new work is pulled.
Kanban is more prescriptive than Scrum in managing queues. The Kanban control mechanism allows for continuous adjustment, in contrast to Scrum, which relies on the team commitment, reviewed at sprint boundaries. Kanban can readily be used inside the sprint boundaries to keep WIP low.