The data access level provides optimized data access methods and carries on the connection with the courseware database.

数据访问层提供优化的数据访问方法，与课件数据库进行连接；

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The data access level provides optimized data access methods and carries on the connection with the courseware database.

数据访问层提供优化的数据访问方法，与课件数据库进行连接；

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