例如，在系统类别载入器类别空间中的类别，不应当指向孩子或子孙类别载入器的类别空间中的类别。

For instance, classes in the system class loader class space should not refer to classes in the class space of a child or a descendant class loader.

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尽管在本体中服务是作为元素的子类而定义的，但是它也提到，上层类别(如系统)的实例提供的能力也可视为服务。

Although ontology defines a service as a subclass of element, it states that instances of higher level classes, for example, systems may provide capabilities that can be offered as services.

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这一部分介绍如何访问两类系统元数据：类别模式和关系。

This section discusses how to access two types of system metadata: the category schema and the relationships.

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