| 摘要 |
To manage forward and backward compatibility, a mechanism is provided through which evolved and synthesized property definitions may be added by a new implementation that uses data from an old implementation. The definitions are associated with code that rename, reformat or otherwise manage access to the properties for which an old schema and a new schema are different. Such mechanisms generally allow an application using a first implementation of a metadata schema to access data stored using a second implementation of a metadata schema by specifying an evolved property definition in the first implementation to refer to a corresponding property definition in the second implementation, for each property in the first implementation that is different from a corresponding property in the second implementation. Accesses are redirected using the evolved property definition to access the corresponding property definition in the second implementation. Also, such mechanisms generally allow an application using a first implementation of a metadata schema to access data stored using a second implementation of a metadata schema, by specifying a synthesized property definition in the first implementation for each property in the first implementation that lacks a corresponding property definition in the second implementation. Information about accesses to the synthesized property definition then is maintained during use of the second implementation.
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