1. A network element for a software-defined network, the network element comprising a data transfer interface for transmitting data to the software-defined network and for receiving data from the software-defined network, and a processing system adapted to: construct, in accordance with configuration data received from a controller system of the software-defined network, a configuration system for managing data to be forwarded so as to enable the network element to operate as a part of the software defined network, configure a first portion of the configuration system to associate, with data received at the network element, a configuring entity-specific identifier identifying a configuring entity related to the received data, the configuring entity-specific identifier constituting at least a part of metadata associated with the received data, and configure second portions of the configuration system, which are used subsequently to the first portion of the configuration system, to use the metadata comprising the configuring entity-specific identifier when determining actions to be carried out in conjunction with the received data.