Synchronize 2 UR databases

[xja]

How about being able to synchronize 2 UR databases, even if it is just one-directional, just to facilitate incremental backups to a local drive, so we don't have to copy the entire database to back it up.

ie, even this simple type of sync would be very helpful
- items in database A but not in database B are copied to B
- items in B but not in A are deleted from B
- items in A that are newer than B are copied to B

Doing this across a network would be cool, but that seems a lot trickier when you are dealing with large databases.