上一篇《Using SQL Server DB for DSC》中，核心机制就是这个图：
我一开始的理解是这样的，并且很长时间这么理解
还惊讶于“双向同步”的设计。
其实并不是这样的
When you link to a table in an Access database, Access creates a new table, called a linked table, which maintains a link to the source records and fields. Any changes you make to the data in the source database are reflected in the linked table in the destination database, and vice versa.
https://support.microsoft.com/en-us/office/import-or-link-to-data-in-another-access-database-095ab408-89c7-45b3-aac2-58036e45fcf6#Link to data in another Access database
Although linked tables can be used as regular Microsoft Access Database tables, it’s important to keep in mind that they aren’t actually stored in the Microsoft Access database. Each time data is viewed in a linked table, Microsoft Access has to retrieve records from another file. This can take time, especially if the linked table is on a network or in an SQL database.
http://www.eident.co.uk/2017/03/performance-microsoft-access-databases/
所以，Access本身并不存储数据，只是通过ODBC driver发送数据库操作到SQLServer。当你打开.mdb文件看到数据是因为做了一次查询而已。
