A method for optimizing entity-specific configuration systems for functional entities of a network element of a software-defined network is presented. The entity-specific configuration systems are based on a network element-specific configuration system related to the whole network element and comprising configuration entries for determining operations to be carried out by the network element. The method comprises forming (401) relation data that indicates, for each of the functional entities, those of the configuration entries which are irrelevant to the functional entity under consideration so that operation of the functional entity is independent of these configuration entries. The relation data enables the entity-specific configuration systems to be constructed (402) so that the entity-specific configuration system of each functional entity is free from those configuration entries which, according to the relation data, are irrelevant to the functional entity under consideration. Therefore, resources for implementing the entity-specific configuration systems can be saved.