1. A method for storing subscriptions for a publish-subscribe network, comprising: specifying a structure to store a subscription in the network; dividing the structure into a plurality of sub-expressions; using the sub-expressions to collectively specify a particular subscription; and associating a Boolean-valued predicate with at least one of the sub-expressions for the particular subscription, wherein the Boolean valued predicate provides an indication of a notification element for the particular subscription in order to provide content-based routing for the subscription.