This is necessary to isolate the relational layer from the object layer, but this convenience comes at the cost of performance.

这对于将关系层与对象层分离是必需的，但这种便利是以牺牲性能为代价获得的。

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Performance is now nearly equal to that of using a mapped object.

现在，性能几乎与使用映射对象的性能相同。

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The first level consists of the performance object, which is a unit that can model a physical device or abstract component in a system.

第一级包括性能对象，它是可以为物理设备建模，或者抽象系统中组件的单元。

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