P DO的易用性使之在直接处理数据库时很自然地成为了首选方法，就因为这一原因，SDO提供的关系型DAS实现也选择了此技术。

The ease of use of PDO makes it a natural choice when working directly with databases, and for this very reason is the technology chosen for the Relational DAS implementation provided with SDO.

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例如，如果数据库不是任务关键型和24x7型的，那么停机上一段时间和丢失一些数据可能是可以接受的，对于媒介错误，重新键入数据也可能是一种可以接受的方法。

For instance, if the database is not mission-critical and 24x7, some downtime and loss of data may be acceptable, and re-keying of data may be an acceptable option should media failure occurs.

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在设计层次型数据库时，一个较好的设计方法是分二步走：首先利用实体联系方法抽象出现实世界的实体联系模型，然后将实体联系模型变换到具体DBMS 所支持的层次型模型。

A good algorithm to design such a hierarchical database consists of two steps, first, to describe real world in E-R model and then, convert it to the model supported by the DBMS.

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