In a method of operating a data network comprising a plurality of interconnected nodes (30) each of which is operable to perform one or more services upon receiving a suitable request for a service, one or more user devices (10) connected to the network can issue requests (12, 14) for a service to be carried out by a node or nodes within the network. The method comprises: operating a virtual mechanism (50) in which a plurality of different types of elements (61, 65, 66, 67) are represented, each element obeying a set of rules associated with the respective type of the element, the respective set of rules specifying how the element behaves, wherein the probabilistic rules governing the creation, destruction and alteration of the elements are arranged to ensure that the total population of elements per node, and/or the total number of each type of element per node tends to remain below a certain settable threshold population whereby the mechanism can generally be operated without requiring elements to be dropped because of a lack of hardware processing resources, thereby maintaining the efficiency of the mechanism.