生鱼片模型 Sashimi Model
生鱼片模型是改进的瀑布模型，有如下的优点和缺点：
Overlapping phases 阶段之间可以重叠
Advantages
Reduces overall schedule
Reduces documentation
Works well if personnel continuity
Disadvantages
Milestones more ambiguous
Progress tracking more difficult 过程跟踪会变得困难
Communication can be more difficult
