Semantics of an NIS (Contd.)
One approach is to make registration cycles illegal.
How can we detect cycles?
- When a new source is registered, we can check to see if this causes a cycle to be formed. Requires cooperation among gestalt sites.
- At query evaluation time, an id can be assigned to each query (and all the subqueries it generates), and this can be used to detect cycles. (Cooperation reqd.)