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Scrum is a lightweight agile method for software development. Scrum is named after the Scrum in rugby, which is a way to restart the game after an accidental infringement. This entry describes the software development part of Scrum.
Scrum was first applied in 1993 at Easel Corporation by Jeff Sutherland, John Scumniotales and Jeff McKenna when building an object-oriented design and analysis (OOAD) tool incorporating Round-trip engineering. At that time they needed a development method that had rapid application development and where product requirements could easily be translated into working code. These principles later became some of the basics of Scrum.
Characteristics
Scrum assumes that the software development process is complicated and unpredictable and treats it as a controlled black box instead of a theoretical, fully-defined process. This is one of the biggest differences between Scrum and the Waterfall and Spiral methodologies, which view the software development process as a fully defined process. Most problems encountered when using these older, formal types of methodologies are:
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- Requirements are not fully understood at the beginning of the process.
- Requirements change during the process.
- The process becomes unpredictable when new tools and technologies are used.
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Another characteristic of Scrum is that the software development process isn’t treated as a linear process, unlike the Waterfall, Spiral and Iterative methodologies. In a lot of cases this linear process consists of the following four activities: Analysis, Design, Implementation and Testing. Scrum, however, doesn't prescribe a sequence in which the activities must be implemented. A project can start with any activity, and can change between activities at any time. This increases the project's flexibility and productivity.
To manage these processes with flexibility, Scrum supplies techniques and controls to manage this unpredictable process.
Development Phase Techniques
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- Team creation
- Scrum believes that a development team should perform as a sport team, every team member working independently but towards the same goal. Scrum suggests that a team has a maximum of 6 - 7 members. The team facilitator is called the Scrum master. His/her job is to implement and manage the Scrum process in the project. The Scrum team as a whole defines the practices, meetings, artifact and terminology of SCRUM for the team, and the Scrum Master ensures adherence to these "norms" identified. Scrum masters serve a facilitator role and their authority is mostly indirect. Scrum masters focus most of their time in managing outside interference for the Scrum team and solving outside impediments or ‘Blockers’ that cannot be solved by the Scrum team. The master also focuses on ensuring transparency into the development process by maintaining the multiple Scrum artifacts defined elsewhere in this article.
- Backlog creation
- There are 3 types of backlogs:
- Product - Acts as a reposititory for requirements targeted for release at some point. These are typically high level requirements with high level estimates provided by the product stakeholders.
- Release - Requirements pulled from the product backlog and identified and prioritized for an upcoming release. The release backlog contains more details about the requirement and low level estimate which are usually estimated by the team performing the work.
- Sprint - At the beginning of each sprint, the team has sprint planning with an end result being a backlog of requirements/sub-requirements that the team anticipates completing at the end of the sprint. By completing, that means fully coded, tested and documented. These are the items that the team will "Burndown" against throughout the duration of the sprint.
- The sprint backlog breaks the release backlog requirement into manageable chunks that can be accomplished typically in 8 - 16 hrs.
- Project segmentation
- The whole project gets divided into periods of time with a maximum duration of 4 weeks. One period is called a Sprint and every team gets a backlog to execute within the given Sprint.
- Scrum meetings
- During the sprint, the team conducts daily scrum meetings.
- The meetings are held in the same place at the same time every work day.
- The meetings don’t last for more than 30 minutes.
- A scrum master is appointed.
- The scrum master is responsible for asking every team member the following three questions:
- What have you done since the last scrum meeting?
- What has impeded your work?
- What do you plan on doing between now and the next scrum meeting?
- Conversation is restricted to the team members answering the above questions.
- Meetings can be established for immediately after the scrum meeting based on answers to the above questions.
- The scrum master is responsible for making decisions immediately, if required to remove impediments to progress.
- The scrum master is responsible for noting impediments that must be resolved external to the meeting and causing them to be removed.
- Phases
- The Scrum development process consists of 5 major activities “Review release plans”, “Distribution, review and adjustment of product standards”, “Sprint”, “Sprint review” and “Closure”.
- Sprint
- The Sprint phase is where the software development takes place. A Sprint consists of the following sub-activities: Develop, Wrap, Review and Adjust. This phase has no sequence. Sometimes a backlog item must be developed, wrapped and reviewed and sometimes a backlog item must be only reviewed or adjusted. It totally depends on the backlog item.
- Sprint review
- Each Sprint is followed by a Sprint review. During this review the software developed in the previous Sprint is reviewed and if necessary new backlog items are added. The reviewers consist of project stakeholder, managers, developers and sometimes customers, sales and marketing.
- The activities, Sprint and Sprint review are repeated until the product is deemed ready for distribution by the project stakeholders. Then the project goes into the closure phase where the product is made ready for release and distribution.
- Closure
- In this stage activities like last debugging, marketing and promotion take place. By finishing this activity the project is closed. Because of the unpredictability of the software development process it’s not possible to define exactly when this activity will take place and so the project may take shorter or longer than planned. But by using the controls given by Scrum one can make calculations on the duration of the project.
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