Essentially,
you can allow a user from one database to interact with another (local) database without explicitly
adding that user and giving her object or schema rights. I??™ve taught this topic many times, but for a long
time I had difficulty coming up with a realistic business scenario in which to use it. Now I have one.
When you need a quick restore, it may be beneficial to create a separate database just for the
purposes of backup and restore. You could then use impersonation to integrate it with the primary
database, yet back it up and restore it with a completely separate approach. This way, you could
effectively partition a system into two separate databases with completely different restore and
availability needs.
Yes, you could achieve the same sort of functionality using filegroup backups. And yes, there is
potentially a major issue with database design and maintaining transactional consistency between the
two databases. However, in the example of a manifest-creation system, you could restore that ???subdatabase???
without disrupting the larger system. Even a single filegroup restore has some impact on
a large database, as transaction logs must be restored to achieve transactional consistency.
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