The facade is a class that provides a set of methods that can create data objects from the back end, or provide some other business function.
虚包是包含一套方法的类，利用它，你可以从后台创建数据对象，或提供一些其它的业务功能。
A data warehouse will normally be presented as a set of tables, which requires an end user to have knowledge of what tables and columns are relevant and how to join the tables together.
数据仓库一般表示为一组表，它要求最终用户知道哪些表和列是相关的以及如何将表联结在一起。
When all the data have been written, set the eof (end-of-file) argument.
当所有数据全部写入之后，就需要设置eof(文件结束参数)。
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