One thing to note: the first elementof the arrray is the top of the call trace, not the last.
有一点要注意：数组的第一个元素（而不是最后一个元素）是这个调用跟踪的栈顶。
2
This query starts at a context element and follows all trace relationships in the reverse direction to discover all elements in lower levels of abstraction.
这个查询是从一个上下文元素开始的，并遵照相反方向的跟踪关系从而发现更低抽象层的同一水平的元素。
3
When an elementof the requirements chain changes, all the trace relationships are marked as suspect, as shown in Figure 28.