Abstract: In a publish/subscribe system, a plurality of publishers provide information on a range of topics and a plurality of subscribers subscribe to one or more topics and topic sets on which they wish to receive information. Subscribers can also unsubscribe from topics and topic sets on which they do not wish to receive information. A subscription matcher such as a message broker is used to generate a subscription list of topic and topic set identifiers—from both the subscribe and unsubscribe requests of each subscriber. The subscription matcher then matches items of information from each publisher with topics and topic set definitions in the subscription list of each subscriber, and distributes matched items of information in accordance with subscription lists. The subscription matcher determines precedence between any overlapping subscribed and unsubscribed topics and topic sets based on the sequence in which they were stored.

Abstract: A method of distributing messages from a server system to a plurality of client systems comprises defining a quality of service (QoS) level for messages provided by the messaging system to the client system, defining a message processing capacity provided by a client to the messaging system, and degrading the QoS level of messages in the event that the client system does not provide the defined message processing capacity to the messaging system.