| Software development process |
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| Activities and steps |
| Methodologies |
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Scrum is an iterative, incremental framework for project management often seen in agile software development, a type of software engineering.
Although the Scrum approach was originally suggested for managing product development projects, its use has focused on the management of software development projects, and it can be used to run software maintenance teams or as a general project/program management approach.
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In 1986, Hirotaka Takeuchi and Ikujiro Nonaka described a new approach to commercial product development that would increase speed and flexibility, based on case studies from manufacturing firms in the automotive, computer, photocopier, and printer industries.[1] They called this the holistic or rugby approach, as the whole process is performed by one cross-functional team across multiple overlapping phases, where the team "tries to go the distance as a unit, passing the ball back and forth".[1]
In 1991, DeGrace and Stahl first referred to this as the scrum approach[2] In rugby, a scrum refers to the manner of restarting the game after a minor infraction. In the early 1990s, Ken Schwaber used such an approach at his company, Advanced Development Methods, and Jeff Sutherland, with John Scumniotales and Jeff McKenna, developed a similar approach at Easel Corporation, and were the first to refer to it using the single word Scrum.[3]
In 1995, Sutherland and Schwaber jointly presented a paper describing the Scrum methodology at the Business Object Design and Implementation Workshop held as part of OOPSLA ’95 in Austin, Texas, its first public presentation.[4] Schwaber and Sutherland collaborated during the following years to merge the above writings, their experiences, and industry best practices into what is now known as Scrum.
In 2001, Schwaber teamed up with Mike Beedle to describe the method in the book Agile Software Development with Scrum.[5]
Although the word is not an acronym, some companies implementing the process have been known to spell it with capital letters as SCRUM. This may be due to one of Ken Schwaber’s early papers, which capitalized SCRUM in the title.[6]
Scrum is a process skeleton that contains sets of practices and predefined roles. The main roles in Scrum are[7]:
A sprint is the basic unit of development in Scrum. Sprints tend to last between one week and one month,[6] and are a "timeboxed" (i.e. restricted to a specific duration) effort of a constant length.[8]
Each sprint is preceded by a planning meeting, where the tasks for the sprint are identified and an estimated commitment for the sprint goal is made, and followed by a review or retrospective meeting,[9] where the progress is reviewed and lessons for the next sprint are identified.
During each sprint, the team creates a potentially deliverable product increment (for example, working and tested software). The set of features that go into a sprint come from the product “backlog”, which is a prioritized set of high level requirements of work to be done. Which backlog items go into the sprint is determined during the sprint planning meeting. During this meeting, the Product Owner informs the team of the items in the product backlog that he or she wants completed. The team then determines how much of this they can commit to complete during the next sprint, and records this in the sprint backlog.[6] During a sprint, no one is allowed to change the sprint backlog, which means that the requirements are frozen for that sprint. Development is timeboxed such that the sprint must end on time; if requirements are not completed for any reason they are left out and returned to the product backlog. After a sprint is completed, the team demonstrates how to use the software.
Scrum enables the creation of self-organizing teams by encouraging co-location of all team members, and verbal communication between all team members and disciplines in the project.
A key principle of Scrum is its recognition that during a project the customers can change their minds about what they want and need (often called requirements churn), and that unpredicted challenges cannot be easily addressed in a traditional predictive or planned manner. As such, Scrum adopts an empirical approach—accepting that the problem cannot be fully understood or defined, focusing instead on maximizing the team’s ability to deliver quickly and respond to emerging requirements.
Like other agile development methodologies, Scrum can be implemented through a wide range of tools. Many companies use universal software tools, such as spreadsheets to build and maintain artifacts such as the sprint backlog. There are also open-source and proprietary software packages dedicated to management of products under the Scrum process. Other organizations implement Scrum without the use of any software tools, and maintain their artifacts in hard-copy forms such as paper, whiteboards, and sticky notes.[10]
Scrum teams consist of three core roles and a range of ancillary roles—core roles are often referred to as pigs and ancillary roles as chickens (after the story The Chicken and the Pig).
The core roles in Scrum teams are those committed to the project in the Scrum process—they are the ones producing the product (objective of the project).
The ancillary roles in Scrum teams are those with no formal role and infrequent involvement in the Scrum process—but nonetheless, must be taken into account.
Scrum has not only reinforced the interest in software project management, but also challenged the conventional ideas about such management. Scrum focuses on project management institutions where it is difficult to plan ahead with mechanisms for empirical process control, such as where feedback loops constitute the core element of product development compared to traditional command-and-control oriented management. It represents a radically new approach for planning and managing software projects, bringing decision-making authority to the level of operation properties and certainties. Scrum reduces defects and makes the development process more efficient, as well as reducing long-term maintenance costs.[6]
At the end of a sprint cycle, two meetings are held: the “Sprint Review Meeting” and the “Sprint Retrospective”
The product backlog is a high-level list that is maintained throughout the entire project. It aggregates backlog items: broad descriptions of all potential features, prioritized as an absolute ordering by business value. The features added to the backlog are commonly written in story format (See terminology below). The product backlog is the “What” that will be built, sorted by importance. It is open and editable by anyone, but the product owner is ultimately responsible for sorting the stories on the backlog for the team. The product backlog contains rough estimates of both business value and development effort, these values are often stated in story points using a rounded Fibonacci sequence. Those estimates help the Product Owner to gauge the timeline and, to a limited extent prioritize. For example, if the “add spellcheck” and “add table support” features have the same business value, the one with the smallest development effort will probably have higher priority, because the ROI (Return on Investment) is higher.
The Product Backlog, and business value of each listed item is the property of the product owner. The associated development effort is however set by the Team.
The sprint backlog is the list of work the team must address during the next sprint. The list is derived by selecting stories/features from the top of the product backlog until the team feels they have enough work to fill the sprint. This is done by the team asking "Can we also do this?" and adding stories/features to the sprint backlog. The team should keep in mind their previous sprints velocity(total story points from the last sprints stories) when selecting stories/features for the new sprint and use this number as a guide line of how much "effort" they can complete.
The stories/features are broken down into tasks by the team, which, as a best practice, should normally be between four and sixteen hours of work. With this level of detail the whole team understands exactly what to do, and potentially, anyone can pick a task from the list. Tasks on the sprint backlog are never assigned; rather, tasks are signed up for by the team members as needed during the daily scrum, according to the set priority and the team member skills. This promotes self-organization of the team, and developer buy-in.
The sprint backlog is the property of the team, and all included estimates are provided by the Team. 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”.
The sprint burn down 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. There are also other types of burndown, for example the release burndown chart that shows the amount of work left to complete the target commitment for a Product Release (normally spanning through multiple iterations) and the alternative release burndown chart,[17] which basically does the same, but clearly shows scope changes to Release Content, by resetting the baseline.
It should not be confused with an earned value chart.
The following terminology is used in Scrum:[18]
Scrum-ban is a software production model based on Scrum and Kanban. Scrum-ban is especially suited for maintenance projects or (system) projects with frequent and unexpected user stories or programming errors. In such cases the time-limited sprints of the Scrum model are of no appreciable use, but Scrum’s daily meetings and other practices can be applied, depending on the team and the situation at hand. Visualization of the work stages and limitations for simultaneous unfinished user stories and defects are familiar from the Kanban model. Using these methods, the team’s workflow is directed in a way that allows for minimum completion time for each user story or programming error, and on the other hand ensures each team member is constantly employed.[22]
To illustrate each stage of work, teams working in the same space often use post-it notes or a large whiteboard.[23] In the case of decentralized teams, stage-illustration software, such as Assembla, ScrumWorks, Rational Team Concert or JIRA in combination with GreenHopper can be used to visualize each team’s user stories, defects and tasks divided into separate phases.
In their simplest, the tasks or usage stories are categorized into the work stages
If desired, though, the teams can add more stages of work (such as “defined”, “designed”, “tested” or “delivered”). These additional phases can be of assistance if a certain part of the work becomes a bottleneck and the limiting values of the unfinished work cannot be raised. A more specific task division also makes it possible for employees to specialize in a certain phase of work.[24]
There are no set limiting values for unfinished work. Instead, each team has to define them individually by trial and error; a value too small results in workers standing idle for lack of work, whereas values too high tend to accumulate large amounts of unfinished work, which in turn hinders completion times.[25] A rule of thumb worth bearing in mind is that no team member should have more than two simultaneous selected tasks, and that on the other hand not all team members should have two tasks simultaneously.[24]
The major differences between Scrum and Kanban are derived from the fact that, in Scrum work is divided into sprints that last a certain amount of time, whereas in Kanban the workflow is continuous. This is visible in work stage tables, which in Scrum are emptied after each sprint. In Kanban all tasks are marked on the same table. Scrum focuses on teams with multifaceted know-how, whereas Kanban makes specialized, functional teams possible.[26]
Since Scrum-ban is such a new development model, there is not much reference material. Kanban, on the other hand, has been applied in software development at least by Microsoft and Corbis.[27]
Scrum as applied to product development was first referred to in "New New Product Development Game" (Harvard Business Review 86116:137–146, 1986) and later elaborated in "The Knowledge Creating Company" both by Ikujiro Nonaka and Hirotaka Takeuchi (Oxford University Press, 1995). Today there are records of Scrum used to produce financial products, Internet products, and medical products by ADM.
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