ontape/ondatartr restores

It's well known that OnLine demands that a restore requires the original chunks to be available, or at least the same symbolic links. But why is this? I can't understand why, since the physical location of pages is unimportant. The important thing is the relative address of each page wrt the start of its dbspace. Other DBMSs, e.g. Adabas, work entirely on relative address blocks (pages). This makes transfer of data between servers, or between prod and dev on the same server, much easier. Neil Truby Chase Manhattan Bank Bournemouth, UK