尽管我们不会重用实际的约束实现，但是元数据api提供一些方法来提取约束定义并重用它。

While we do not reuse the actual constraint implementation, the metadata API offers some ways to extract the constraint definition and reuse it.

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这种元数据API不仅定义关系数据存储中数据的形式，而且定义与该数据相关联的查询，并建立了不同对象之间的关系。

This metadata API not only defines the shape of the data in the relational data store, but also defines the queries associated with that data and establishes relationships between different objects.

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SDO还提供了一个元数据api，允许应用程序、工具和框架对数据图形的数据模型进行自检。

SDO also provides a metadata API, which allows applications, tools, and frameworks to introspect the data model for a data graph.

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