A processing node for processing data items in a data network, comprising means for receiving data items, means for receiving characterisation metrics associated with the data items and identifying characteristic values in respect thereof, and a process selection means, said process selection means comprising means for deriving a collective value from characteristic values associated with a plurality of the data items, means for comparing characteristic values associated with a plurality of the data items with a predetermined target value, means for subjecting data items in respect of which the characteristic values are on a first side of the predetermined target value to a first process, means for selecting at least some of the data items in respect of which the characteristic values are on a second side of the predetermined target value, and means for subjecting the selected data items to a second process which is different from the first process.