1. A messaging system for use in a network, the messaging system comprising: a plurality of network entities which include both publishing entities and subscribing entities, the publishing entities having data of which the subscribing entities have need; and a data hierarchy applied to the data exchanged between the publishing entities and subscribing entities; wherein the data hierarchy determines the virtual connections formed between the plurality of network entities in response to publication and subscription requests exchanged between the entities, such that the virtual connections established between network entities form a hierarchy corresponding to the data hierarchy.