A computer implemented method to specify a software defined network (SDN) for deployment by an SDN controller, the SDN controller being adapted to configure a plurality of physical network components to deliver communication services, the method including generating a model of the physical network components by accessing each of a plurality of data sources; defining the model including an indication of a location, type and interconnections of physical components based on the data sources; associating each indication in the model with a degree of confidence of accuracy of the indication based on the degree of confidence information from the data sources; accessing a set of rules defining relationships between types of physical component; refining the model based on the rules including adjusting a degree of confidence of accuracy of indications in the model based on satisfaction of the rules; and selecting a subset of network components in the refined model for inclusion in the SDN specification.