1·Each datum has a unique key.
每个数据都有一个独特的键。
2·Any query such as the one in Listing 1 has a precise path to the specified datum, which a DBMS can quickly determine in balanced trees and byte-offset codings.
如清单 1 中所示的任何查询都有到指定数据的精确路径，DBMS 可以迅速地在均衡树和字节偏移编码中确定它。
3·While it's possible to capture a whiteboard drawing digitally, it's generally an expensive operation, and the resulting datum is clumsy to transmit, version, archive, validate, and transform.
虽然以数字化的方式获取白板上的绘图是可能的。但这么做的代价通常很昂贵，并且所产生的数据难于发送、控制版本、归档、验证、转换。
4·Documents are one datum typically shoe-horned into rows and columns; irregular data is a mismatch for RDBMSs, as well.
文档是一种通常按行和列填充的数据，不规则的数据也不适合于 RDBMS。
5·The fourth column shows the index type (as defined in the schema in Listing 5) used to represent the datum.
第四列将显示用于表示数据的索引类型(按照清单5的模式中的定义)。