My project at Dartmouth, called Snowflake, approaches this problem with a philosophy of user-level aggregation. In order for a single-system image to span administrative domains, it can't be constructed by the system administrator. Instead, system administrators export raw resources under some access-control policy. Then users have the freedom to aggregate those resources into a single system image.

Our user above has aggregated some resources from two departments into his own, personal single-system image that spans administrative boundaries. If he later acquires access to new resources, he can integrate those into his system, preserving uniform access to all of ``his'' resources.