1. A computer implemented method for optimizing query evaluation and processing services in a subscription notification system to reduce query redundancy at a notification service provider system of the subscription notification system, comprising: receiving a set of subscription queries at a notification broker system from subscription client systems, the notification broker system comprising processing circuitry and acting as an intermediary between the subscription client systems and the notification service provider system; as the subscription queries are received from subscription client systems at the notification broker system, generating a classification tree by analyzing the subscription queries to determine hierarchical relationships among the subscription queries and to identify subscription queries that are subsets of corresponding other subscription queries; selecting one of the nodes in the classification tree as the basis for an optimal subscription query, the selection based upon a minimum number of relevant messages expected to be obtained via execution of the selection; generating the optimal subscription query from selected node, the optimal subscription query including all query elements from the selected node and all of the query elements from child nodes of the selected node; subscribing the notification broker system to the notification service provider system with the optimal subscription query; receiving at least one notification message from the notification service provider system in response to the optimal subscription query from the notification broker system; and identifying subscription client systems for transmitting the at least one notification message resulting from execution of the optimal subscription query by identifying the one or more selected nodes that match the optimal subscription query for which the at least one notification message is generated, and transmitting the at least one notification message to subscriber client systems associated with the one or more selected nodes.