This means that every row in the point table must have a key value (consisting, in this case, of two column values) that must also exist in the source table.
这意味着点表中每一行的键值（在这个示例中，由两个列值组成）必须也在源表中存在。
Table 4 shows the key values measured for the two configurations.
表4展示了两个配置的关键度量值。
A dictionary in Objective-C is an object that holds two sets of information, a unique key and associated values, and enables you to use the key to retrieve items.
Objective - c中的字典是一个具有两组信息(惟一的密钥和相关的值)的对象，且使您能够使用该密钥来检索条目。
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