Pattern of the Month: Timebox
This month's pattern of the month takes a look at the time-limiting principle of timeboxing and how it applies to Scrum.
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A timebox is a period of fixed maximum duration in which team activities may be carried out. In Scrum, there are five timeboxed events: Sprint Planning, the Daily Scrum, the Sprint Review, the Sprint Retrospective, and the Sprint itself which is a timebox containing all other events. In Agile practice, the delivery of value should not be put in unnecessary delay. Brisk timeboxing can help, since events are often subject to the law of diminishing returns.
For example, it’s unlikely that spending two working days on Sprint Planning will be twice as effective as one working day. It is believed that the purposes of Sprint Planning may be reasonably accomplished in 8 hours or less. Any longer is not likely to improve the quality of the activity, and it would be better to commence work and learn from actual experience, inspecting and adapting the Sprint Backlog accordingly.
In Scrum, each event is a timeboxed opportunity to inspect and adapt something. The Daily Scrum encourages the team to replan their forecast of work continually during the Sprint, based on experience. A Sprint Review allows the increment to be inspected, and the Product Backlog adapted, to reflect the total work for the Product which is believed to remain. A Sprint Retrospective, meanwhile, is a formal opportunity to inspect and adapt the team's implementation of Scrum.
Not all of the activities performed by a team need to be timeboxed. Product Backlog refinement, for example, is an ongoing activity for which timeboxing is optional. Teams should simply reserve enough time to refine the Product Backlog in advance of the next Sprint. Yet Product Backlog refinement is instrumental in de-risking Sprint Planning by ensuring that items are "ready," well understood, and hold no surprises or unknowns which would require extended discussion. If multiple teams must collaborate to create a "Done" increment, it might thus become necessary to formalize the activity as a timebox. In Scaled Professional Scrum, each team in a Nexus is expected to do so.
Timebox is Pattern of the Month at Agilepatterns.org
Intent: Limit the time that is available for a task in order to avoid procrastination
- "Work expands to fill the time available." (Parkinson’s Law)
- "Time is not so important as making time count."
Also Known As:
- Time Limited Activity
Motivation: Work that does not have a clear deadline is likely to be delayed, while focus on the completion of core requirements may be lost. If the time available is limited, it helps to provide a focus, and increases the chances of the essential scope being addressed within the allotted time span.
Structure: A time-limitable event, such as a meeting or project, will have a backlog of items for action. A team will plan to action certain items from the backlog in an iterative manner. Each iteration will be time-boxed to be of a certain length. At the end of the time-box, the success of the iteration can be reviewed, and the process followed can be retrospectively adapted. Each time-boxed iteration will produce metrics that can be inspected and compared for this purpose. The early delivery of value does not shorten a time-box; it will terminate at the predetermined time. Note that it should only possible to abandon a time-box in very exceptional and clearly defined circumstances.
Applicability: In Agile practice, time-boxing is appropriate for any activity that is expected to deliver a result of value. It would be highly irregular in any Agile way of working to conduct an activity that is not time-boxed.
Consequences: The time-boxing of an activity can increase focus on the delivery of value. However, it also incurs the risk that not all planned items will be actioned within the allocated time. The prioritization of backlog items is therefore important.
Implementation: In Scrum, Sprints are time-boxed to a length of no more than one calendar month. Reviews, Retrospectives, Planning Sessions, and Daily Stand-ups are also time-boxed.
- Unbounded Timebox
- Time Theft
- Parkinson's Law, The Economist
- Timebox, Agile Alliance
- Timebox or Kanban: A False Dichotomy, by Johanna Rothman
- Timeboxing, DSDM Consortium
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