Based on our observation about the likely relationship among subscriptions, the strategy works as follows. When a subscription reaches a server (either from a client or from another server), the server propagates that subscription only if it defines new selectable notifications that are not in the set of selectable notifications defined by any previously propagated subscription. Three bene- fits accrue from this approach. First, we reduce network costs by pruning the propagation of new subscriptions. Second, we reduce the storage requirements for servers. Third, by reducing the number of subscriptions held at each server, we reduce the computational resources needed to match notifications at that server. We use a.
