. Bower (2008) then proposed a design methodology of five stages: (1) identifying educational goals, (2) postulating suitable tasks, (3) determining the affordance requirements of the task, (4) determining the affordances available and (5) designing the e-learning task, which serves as a guideline of how technology adoption can best meet the requirements of learning tasks.

表示的就是使用了覆盖索引，性能上会快很多