| Software development process | |
|---|---|
| Activities and steps | |
| Requirements · Specification Architecture · Design Implementation · Testing Deployment · Maintenance | |
| Models | |
| Agile · Cleanroom · DSDM Iterative · RAD · RUP · Spiral Waterfall · XP · Scrum · Lean V-Model · FDD · TDD | |
| Supporting disciplines | |
| Configuration management Documentation Quality assurance (SQA) Project management User experience design | |
| Tools | |
| Compiler · Debugger · Profiler GUI designer Integrated development environment | |
Although Scrum was intended for management of software development projects, it can be used to run software maintenance teams, or as a general project/program management approach.
History
In 1989, Hirotaka Takeuchi and Ikujiro Nonaka described a new holistic approach that would increase speed and flexibility in commercial new product development.[2] They compared this new holistic approach, in which the phases strongly overlap and the whole process is performed by one cross-functional team across the different phases, to rugby, where the whole team “tries to go to the distance as a unit, passing the ball back and forth”. The case studies came from the automotive, photo machine, computer and printer industries.In 1991, DeGrace and Stahl, in “Wicked Problems, Righteous Solutions,”[3] referred to this approach as Scrum, a rugby term mentioned in the article by Takeuchi and Nonaka. In the early 1990s, Ken Schwaber used an approach that led to Scrum at his company, Advanced Development Methods. At the same time, Jeff Sutherland, John Scumniotales, and Jeff McKenna developed a similar approach at Easel Corporation and were the first to call it Scrum.[4] In 1995 Sutherland and Schwaber jointly presented a paper describing Scrum at OOPSLA ’95 in Austin, TX, its first public appearance. 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.”
Characteristics
Scrum is a “process skeleton,” which contains sets of practices and predefined roles. The main roles in Scrum are:- the “Scrum Master”, who maintains the processes (typically in lieu of a project manager)
- the “Product Owner”, who represents the stakeholders
- the “Team”, a cross-functional group of about 7 people who do the actual analysis, design, implementation, testing, etc.
Scrum enables the creation of self-organizing teams by encouraging co-location of all team members, and verbal communication across all team members and disciplines that are involved 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.
There are several implementations of systems for managing the Scrum process, which range from yellow stickers and whiteboards, to software packages. One of Scrum’s biggest advantages is that it is very easy to learn and requires little effort to start using.
Roles
Main article: The Chicken and the Pig
A number of roles are defined in Scrum. All roles fall into two distinct groups—pigs and chickens—based on the nature of their involvement in the development process. These groups get their names from a joke about a pig and a chicken opening a restaurant:[5]A pig and a chicken are walking down a road. The chicken looks at the pig and says, “Hey, why don’t we open a restaurant?” The pig looks back at the chicken and says, “Good idea, what do you want to call it?” The chicken thinks about it and says, “Why don’t we call it ‘Ham and Eggs’?” “I don’t think so,” says the pig, “I’d be committed, but you’d only be involved.”So the “pigs” are committed to building software regularly and frequently, while everyone else is a “chicken”—interested in the project but really indifferent because if it fails they’re not the pigs—that is, they weren’t the ones that committed to doing it. The needs, desires, ideas and influences of the chicken roles are taken into account, but are not in any way allowed to affect, distort or get in the way of the actual Scrum project.
“Pig” roles
The Pigs are the ones committed to the project in the Scrum process—they are the ones with “their bacon on the line.”- Product Owner
- The Product Owner represents the voice of the customer. He/she ensures that the Scrum Team works with the “right things” from a business perspective. The Product Owner writes customer-centric items (typically user stories), prioritizes them and then places them in the product backlog.
- Scrum Master (or Facilitator)
- Scrum is facilitated by a Scrum Master, whose primary job is to remove impediments to the ability of the team to deliver the sprint goal. The Scrum Master is not the leader of the team (as the team is self-organizing) but acts as a buffer between the team and any distracting influences. The Scrum Master ensures that the Scrum process is used as intended. The Scrum Master is the enforcer of rules. A key part of the Scrum Master’s role is to protect the team and keep them focused on the tasks in hand. The Scrum Master is NOT responsible for the transition from traditional methods of working to Scrum or the implementation of Scrum.
- Team
- The team has the responsibility to deliver the product. A team is typically made up of 5–9 people with cross-functional skills who do the actual work (design, develop, test, technical communication, etc.).
“Chicken” roles
Chicken roles are not part of the actual Scrum process, but must be taken into account. They are people for whom the software is being built.- Stakeholders (customers, vendors)
- These are the people who enable the project and for whom the project will produce the agreed-upon benefit[s], which justify its production. They are only directly involved in the process during the sprint reviews.
- Managers
- People who will set up the environment for the product development organizations.
Meetings
- Daily Scrum
- Each day during the sprint, a project status meeting occurs. This is called a “daily scrum”, or “the daily standup”. This meeting has specific guidelines:
- The meeting starts precisely on time.
- All are welcome, but only “pigs” may speak
- The meeting is timeboxed to 15 minutes
- The meeting should happen at the same location and same time every day
- During the meeting, each team member answers three questions:[6]
- What have you done since yesterday?
- What are you planning to do today?
- Do you have any problems preventing you from accomplishing your goal? (It is the role of the Scrum Master to facilitate resolution of these impediments. Typically this should occur outside the context of the Daily Scrum so that it may stay under 15 minutes.)
- Scrum of scrums
- Each day normally after the daily scrum.
- These meetings allow clusters of teams to discuss their work, focusing especially on areas of overlap and integration.
- A designated person from each team attends.
- The agenda will be the same as the Daily Scrum, plus the following four questions:[7]
- What has your team done since we last met?
- What will your team do before we meet again?
- Is anything slowing your team down or getting in their way?
- Are you about to put something in another team’s way?
- Sprint Planning Meeting[8][9]
- At the beginning of the sprint cycle (every 15–30 days), a “Sprint Planning Meeting” is held.
- Select what work is to be done
- Prepare the Sprint Backlog that details the time it will take to do that work, with the entire team
- Identify and communicate how much of the work is likely to be done during the current sprint
- Eight hour limit
- Sprint Review Meeting[10]
- Review the work that was completed and not completed
- Present the completed work to the stakeholders (a.k.a. “the demo”)
- Incomplete work cannot be demonstrated
- Four hour time limit
- Sprint Retrospective[11]
- All team members reflect on the past sprint
- Make continuous process improvements
- Two main questions are asked in the sprint retrospective: What went well during the sprint? What could be improved in the next sprint?
- Three hour time limit
Artifacts
Product backlog
The product backlog is a high-level document for the entire project. It contains backlog items: broad descriptions of all required features, wish-list items, etc. prioritized by business value. It is the “What” that will be built. It is open and editable by anyone and contains rough estimates of both business value and development effort. Those estimates help the Product Owner to gauge the timeline and, to a limited extent, priority. 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 is higher.The product backlog is the property of the Product Owner. Business value is set by the Product Owner. Development effort is set by the Team. That's it!
Sprint backlog
The sprint backlog is a document containing information about how the team is going to implement the features for the upcoming sprint. Features are broken down into tasks; as a best practice, tasks are normally estimated between four and sixteen hours of work. With this level of detail the whole team understands exactly what to do, and anyone can potentially 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, according to the set priority and the team member skills.The sprint backlog is the property of the Team. Estimations are set by the Team. Often an according Task Board is used to see and change the state of the tasks of the current sprint, like “to do”, “in progress” and “done”.
Burn down
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[12], which basically does the same, but allows to show clearly scope changes into a Release Content, by resetting the baseline.It should not be confused with an earned value chart.
Adaptive project management
The following are some general practices of Scrum:- Customers become a part of the development team (i.e., the customer must be genuinely interested in the output).
- Scrum has frequent intermediate deliveries with working functionality, like all other forms of agile software processes. This enables the customer to get working software earlier and enables the project to change its requirements according to changing needs.
- Frequent risk and mitigation plans are developed by the development team itself—risk mitigation, monitoring and management (risk analysis) occurs at every stage and with commitment.
- Transparency in planning and module development—let everyone know who is accountable for what and by when.
- Frequent stakeholder meetings to monitor progress—balanced dashboard updates (delivery, customer, employee, process, stakeholders)
- There should be an advance warning mechanism, i.e., visibility to potential slippage or deviation ahead of time.
- No problems are swept under the carpet. No one is penalized for recognizing or describing any unforeseen problem.
- Workplaces and working hours must be energized—“Working more hours” does not necessarily mean “producing more output.”
Terminology
The following terminology is used in Scrum:[13]Roles
- Product Owner
- The person responsible for maintaining the Product Backlog by representing the interests of the stakeholders.
- ScrumMaster
- The person responsible for the Scrum process, making sure it is used correctly and maximizes its benefits.
- Team
- A cross-functional group of people responsible for managing itself to develop the product.
- Scrum Team
- Product Owner, ScrumMaster and Team
Artifacts
- Sprint burn down chart
- Daily progress for a Sprint over the sprint’s length.
- Product backlog
- A prioritized list of high level requirements.
- Sprint backlog
- A prioritized list of tasks to be completed during the sprint.
Others
- Impediment
- Anything that prevents a team member from performing work as efficiently as possible.
- Sprint
- A time period (typically 2–4 weeks) in which development occurs on a set of backlog items that the Team has committed to.
- Sashimi
- A slice of the whole equivalent in context to all other slices of the whole. For the Daily Scrum, the slice of sashimi is a report that something is done.
- Velocity
- How much product backlog effort a team can handle in one sprint. This can be estimated by viewing previous sprints, assuming the team composition and sprint duration are kept constant. It can also be established on a sprint-by-sprint basis, using commitment-based planning.
- Abnormal Termination
- The team can cancel a Sprint if they feel they are unable to meet the Sprint Goal. Management can cancel a Sprint if external circumstances negate the value of the Sprint Goal. If a Sprint is abnormally terminated, the next step is to conduct a new Sprint planning meeting, where the reason for the termination is reviewed.
Scrum modifications
Scrum-ban
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 use 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 use stories and defects are familiar from the Kanban model. Using these methods, the team’s workflow is directed in a way which allows for minimum completion time for each use story or programming error, and which on the other hand ensures that each team member is constantly employed. [14]To illustrate each stage of work, teams working in the same space often use post-it notes or a large whiteboard. [15] In the case of decentralized teams stage illustration softwares, such as ScrumWorks and (the combination of) JIRA and GreenHopper can be used to visualize each team’s use stories, defects and tasks divided into separate phases.
In their simplest, the work stages are
- Unstarted
- Ongoing
- Completed
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. [17] 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.[16]
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. [18]
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. [19]
Another new Scrum modification is the 'Tarzan Scrum' which considers the potential benefits of overlapping sprints by considering resources using FIFO. [20]
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