A method, apparatus, and system in which a network system includes a virtual graph composed of a plurality individual networks. A first individual network is associated with a first user. The first individual network includes a plurality of service modules modeled to be representing a first set of network elements. The second individual network is associated with a second user. The second individual network includes a plurality of service modules modeled to be representing a second set of network elements. The second set of network element differs in the type of network elements included in the second individual network and the topological order of the network elements in the second individual network than the first set of network elements.