We have made several assumptions in pursuing this work that have
guided the direction of our research. We have assumed that the network
on which this system will be built is unreliable, and that there is no
guarantee that two arbitrary hosts will always be able to
communicate. We have also assumed a weak-consistency model for caching
where data updates are not propagated to all replicas simultaneously;
it is acceptable to occasionally provide stale data to clients as long
as guarantees are made regarding how out-of-date data is allowed to
become. We will prove the validity of this assumption in
chapter 
.
Finally, we have assumed that ownership of a file is limited to one machine. Changes to a file can only be made by that file's owner, or primary host. This is a characteristic that distinguishes wide-area information systems from distributed file systems or other distributed systems with multiple write privileges. The primary host model simplifies the protocols because they do not need to grant or revoke write privileges, thereby helping to insure that push-caching will scale to millions of hosts.