In terms of cycles and ceremony, Scrum classification is illustrated in Figure 7.1. Scrum is uniquely precise on the length of iterations: usually 30 calendar days, a more-or-less common length compared to other IID methods.
Figure 7.1. Scrum on the cycles and ceremony scale
Scrum is flexible on the ceremony scale; discussion of what and how many workproducts is outside its scope, as is how much rigor is required. As a guiding principle, the Scrum founders would say, "as little ceremony as possible." Also on a Scrum project, the whole team not a manager will decide how much is appropriate.
High levels for a medical device are acceptable, as are low levels for a casual-information read-only Web site.
In terms of scope on the Cockburn scale, Scrum covers the cells shown in Figure 7.2. Although one Scrum team should be seven or less, multiple teams may form a project. It has been used on both small projects and those involving hundreds of developers. Since Scrum practices include working in a common project room, it scales via a "scrum of scrums" where small teams work together and hold a daily stand-up meeting, and representatives from each those teams likewise meet daily. Scrum is complementary enough to other practices that it may be applied across all domains of software applications, from life-critical to more casual and it has.
Figure 7.2. Scrum on the Cockburn scale
Scrum [SB02] is an IID method that emphasizes a set of project management values and practices, rather than those in requirements, implementation, and so on. As such, it is easily combined with or complementary to other methods.
A key Scrum theme is its emphasis on empirical rather than defined process. Ken Schwaber, one of the Scrum founders, tells a noteworthy story in this context [SB02]:
Ogannaike's words echo Deming and Shewhart's industrial process control emphasis on cyclic Plan-Do-Study-Act for complex, changing systems and environments.