Then, this paper deeply investigated the three difficult problems of the system, such as exception handling, security right controlling and heterogeneous database access.

然后，就系统的三个难点问题——异常处理、安全权限控制和异构数据库访问进行了深入的研究。

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Access to heterogeneous databases is provided through requests expressed as queries on a canonical, virtual database.

通过将请求表达成在一个正规、虚拟的数据库上的查询来提供对异种数据库的访问。

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Compared with various DB access methods, database gateway based on ODBC is designed, so as to accomplish centralized backup of heterogeneous DBMS from one point and no configuration at backup side.

通过比较多种数据库访问方法，设计出基于odbc的数据库网关，从而实现从一点集中备份异构数据库和备份端的零配置。

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