Having raised the issue of variations in methods, one classification is their degree of ceremony the amount of method weight in terms of documentation, formal steps, review, and so forth. Another classification is their cycles the number and length of iterations. For example, single-pass waterfall has no iterations; at the other end, an Evo project could have very many one iteration per week. Figure 3.1 illustrates four methods categorized by this scheme.
Figure 3.1. methods by ceremony and cycles
As hinted in Figure 3.1, XP recommends 1 4 weeks, and the UP 2 6 weeks. Some would say the lower left quadrant (many short iterations, low ceremony) describes the agile methods, but this is not quite accurate. For example, Scrum is silent on the question of ceremony or more precisely leaves the question to the discretion of the team. A better way to describe agile methods in terms of ceremony is their promotion of barely sufficient ceremony. That could be high in some case, such as for a USA Food and Drug Administration (FDA) regulated device.