对象数据库：更改类层次结构
我正在读我对面向对象数据库的了解，并且必须做一些演示。
我没有得到也找不到的问题是：
当我更改类层次结构时，数据库的数据会发生什么情况。
例如，我有 A 从 C 扩展。但是后来我注意到 C 必须从 B 扩展，B 必须从 A 扩展：
A <|-- C
A <|-- B <|-- C
我存储在数据库中的（用户）数据会发生什么？
如果数据库不能采用，数据就不能再使用了，对吗？因此，例如，当我有一个社交网络时，所有数据都会丢失，并且网络必须重新开始......我是在这里还是我错过了什么？
I am reading me into object oriented databases right know and have to make a little presentation.
Something I don't get and nowhere can find is following problem:
What happens with the data of the database when I change my class hierarchy.
For example I have A extends from C. But then I notice that C has to extend from B and B has to extend from A:
A <|-- C
A <|-- B <|-- C
What happens to the (user) data I stored in the database?
If the database can't be adopted, the data can't be used anymore, right? So when for example I have a social network all data whould be lost and the network has to start all over again... Am I right here or do I miss something?
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大多数对象数据库都有用于迁移架构然后更新对象的工具。例如，Objectivity/DB 允许开发人员选择是否在单个事务中迁移所有受影响的对象、遇到时迁移它们，还是保留旧格式（例如在只读设备上）并以新格式显示对象。格式。还有广泛的活动模式功能，允许应用程序动态定义、填充、使用和更改对象类。所有这些都可以通过在线系统完成。
http://www.objectivity.com/pages/objectivity /active-schema-dynamic-class-declaration.asp
Most object databases have tools for migrating the schema and then updating the objects. Objectivity/DB, for instance, allows the developer to choose whether to migrate all affected objects in a single transaction, migrate them when encountered, or leave them in the old format (e.g. on a read-only device) and present objects in the new format. There's also an extensive Active Schema capability that allows applications to define, populate, use and change object classes dynamically. All of this can be done with a system online.
http://www.objectivity.com/pages/objectivity/active-schema-dynamic-class-declaration.asp