The product backlog is a breakdown of work to be done and contains an ordered list of product requirements that a scrum team maintains for a product. Common formats include user stories and use cases. The requirements define features, bug fixes, non-functional requirements, etc.—whatever must be done to deliver a viable product. The product owner prioritizes product backlog items (PBIs) based on considerations such as risk, business value, dependencies, size, and date needed.
The product backlog is what will be delivered, ordered into the sequence in which it should be delivered. It is visible to everyone but may only be changed with the consent of the product owner, who is responsible for ordering the product backlog items for the team to work on.
The product backlog contains the product owner’s assessment of business value and may include the team’s assessment of effort or complexity, often, but not always, stated in story points using the rounded Fibonacci scale. These estimates help the product owner to gauge the timeline and may influence the ordering of product backlog items; for example, if two features have the same business value, the product owner may schedule earlier delivery of the one with the lower development effort (because the return on investment is higher) or the one with higher development effort (because it is more complex or riskier, and they want to retire that risk earlier).
The product backlog and the business value of each product backlog item is the responsibility of the product owner. The effort to deliver each item may be estimated in story points, or time. By estimating in story points, the team reduces the dependency in individual developers; this is useful especially in dynamic teams where developers are often assigned to other projects after sprint delivery. For instance, if a user story is estimated as a 5 in effort (using Fibonacci sequence), it remains 5 regardless of how many developers are working on it.
Story points define the effort in a time-box, so they do not change with time. For instance, in one hour an individual can walk, run, or climb, but the effort expended is clearly different. The gap progression between the terms in the Fibonacci sequence encourages the team to deliver carefully considered estimates. Estimates of 1, 2 or 3 imply similar efforts (1 being trivial), but if the team estimates an 8 or 13 (or higher), the impact on both delivery and budget can be significant. The value of using story points is that the team can reuse them by comparing similar work from previous sprints, but it should be recognized that estimates are relative to the team. For example, an estimate of 5 for one team could be a 2 for another having senior developers and higher skills.
Every team should have a product owner, although in many instances a product owner could work with more than one team. The product owner is responsible for maximizing the value of the product. The product owner gathers input and takes feedback from, and is lobbied by, many people, but ultimately makes the call on what gets built.
The product backlog:
- Captures requests to modify a product—including new features, replacing old features, removing features, and fixing issues
- Ensures the developers have work that maximizes business benefit of the product
Typically, the product owner and the scrum team work together to develop the breakdown of work; this becomes the product backlog, which evolves as new information surfaces about the product and about its customers, and so later sprints may address new work.
A product backlog, in its simplest form, is merely a list of items to work on. Having well-established rules about how work is added, removed and ordered helps the whole team make better decisions about how to change the product.
The product owner prioritizes product backlog items based on which are needed soonest. The team then chooses which items they can complete in the coming sprint. On the scrum board, the team moves items from the product backlog to the sprint backlog, which is the list of items they will build. Conceptually, it is ideal for the team to only select what they think they can accomplish from the top of the list, but it is not unusual to see in practice that teams are able to take lower-priority items from the list along with the top ones selected. This normally happens because there is time left within the sprint to accommodate more work. Items at the top of the backlog, the items to work on first, should be broken down into stories that are suitable for the team to work on. The further down the backlog goes, the less refined the items should be. As Schwaber and Beedle put it “The lower the priority, the less detail until you can barely make out the backlog item.
As the team works through the backlog, it must be assumed that change happens outside their environment—the team can learn about new market opportunities to take advantage of, competitor threats that arise, and feedback from customers that can change the way the product was meant to work. All of these new ideas tend to trigger the team to adapt the backlog to incorporate new knowledge. This is part of the fundamental mindset of an agile team. The world changes, the backlog is never finished.
The sprint backlog is the list of work the team must address during the next sprint. The list is derived by the scrum team progressively selecting product backlog items in priority order from the top of the product backlog until they feel they have enough work to fill the sprint. The team should keep in mind its past performance assessing its capacity for the new-sprint, and use this as a guideline of how much ‘effort’ they can complete.
The product backlog items may be broken down into tasks by the developers. Tasks on the sprint backlog are never assigned (or pushed) to team members by someone else; rather team members sign up for (or pull) tasks as needed according to the backlog priority and their own skills and capacity. This promotes self-organization of the developers.
The sprint backlog is the property of the developers, and all included estimates are provided by the developers. Often an accompanying task board is used to see and change the state of the tasks of the current sprint, like to do, in progress and done.
Once a sprint backlog is decided, no additional work can be added to the sprint backlog except by the team. Once a sprint has been delivered, the product backlog is analyzed and reprioritized if necessary, and the next set of functionality is selected for the next sprint.
The increment is the potentially releasable output of the sprint that meets the sprint goal. It is formed from all the completed sprint backlog items, integrated with the work of all previous sprints. The increment must be complete, according to the scrum team’s definition of done (DoD), fully functioning, and in a usable condition regardless of whether the product owner decides to actually deploy and use it.
The following artifacts and techniques can be used to help people use Scrum.
Sprint burndown chart
The sprint burndown chart is a publicly displayed chart showing remaining work in the sprint backlog. Updated every day, it gives a simple view of the sprint progress. It also provides quick visualizations for reference. The horizontal axis of the sprint burndown chart shows the days in a sprint, while the vertical axis shows the amount of work remaining each day (typically representing the estimate of hours of work remaining).
During sprint planning, the ideal burndown chart is plotted. Then, during the sprint, each member picks up tasks from the sprint backlog and works on them. At the end of the day, they update the remaining hours for tasks to be completed. In such a way, the actual burndown chart is updated day by day.
It should not be confused with an earned value chart.
Release burn-up chart
A sample burn-up chart for a release, showing scope completed each sprint (MVP = Minimum Viable Product)
The release burn-up chart is a way for the team to provide visibility and track progress toward a release. Updated at the end of each sprint, it shows progress toward delivering a forecast scope. The horizontal axis of the release burn-up chart shows the sprints in a release, while the vertical axis shows the amount of work completed at the end of each sprint (typically representing cumulative story points of work completed). Progress is plotted as a line that grows up to meet a horizontal line that represents the forecast scope; often shown with a forecast, based on progress to date, that indicates how much scope might be completed by a given release date or how many sprints it will take to complete the given scope.
The release burn-up chart makes it easy to see how much work has been completed, how much work has been added or removed (if the horizontal scope line moves), and how much work is left to be done.
Definition of ready (DoR)
The start criteria to determine whether the specifications and inputs are set enough to start the work item, i.e. a user story.
Definition of done (DoD)
The exit-criteria to determine whether a product backlog item is complete. In many cases, the DoD requires that all regression tests be successful. The definition of done may vary from one scrum team to another but must be consistent within one team.
The total effort a team is capable of in a sprint. The number is derived by evaluating the work (typically in user story points) completed in the last sprint. The collection of historical velocity data is a guideline for assisting the team in understanding how much work they can achieve.
A time-boxed period used to research a concept or create a simple prototype. Spikes can either be planned to take place in between sprints or, for larger teams, a spike might be accepted as one of many sprint delivery objectives. Spikes are often introduced before the delivery of large or complex product backlog items in order to secure budget, expand knowledge, or produce a proof of concept. The duration and objective(s) of a spike are agreed by the team before the start. Unlike sprint commitments, spikes may or may not deliver tangible, shippable, valuable functionality. For example, the objective of a spike might be to successfully reach a decision on a course of action. The spike is over when the time is up, not necessarily when the objective has been delivered.
Also called a drone spike, a tracer bullet is a spike with the current architecture, current technology set, current set of best practices that result in production quality code. It might just be a very narrow implementation of the functionality but is not throwaway code. It is of production quality, and the rest of the iterations can build on this code. The name has military origins as ammunition that makes the path of the bullet visible, allowing for corrections. Often these implementations are a ‘quick shot’ through all layers of an application, such as connecting a single form’s input field to the back-end, to prove the layers connect as expected.
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