Dear friends,
I am using snapshots in ORACLE 8 and am having trouble in refreshing them.

1) What would be appropriate refresh mode that can be used in
updating the snapshots.
2) If an appropriate snapshot is used how should we refresh it and what
is the interval that we can use so that it can update automatically.
3) When I am executing a query on a snapshot and simultaneously if I
update the snapshot, it is showing me 0 results. I believe that is
because it is truncating/deleting the snapshot. Is there any solution to
this so that we can have the updated snapshots while other queries
are accessing the information. If so what would be the way.