Because there are a few OODBs which support the metaclass mechanism, this methodology has limitation to some degree.
但只有少数的OODBs支持元类机制，因此该方法存在一定的局限性。
参考来源 - 部分—整体语义联系和OODBs的集成研究
中间类 - 引用次数：1参考来源 - 分层多媒体数据模型的研究及应用 in C
元类别
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Metaclass
abstract:In object-oriented programming, a metaclass is a class whose instances are classes. Just as an ordinary class defines the behavior of certain objects, a metaclass defines the behavior of certain classes and their instances.