Services delivered via National Infrastructure (NI) are key to securing economic growth and societal well-being. Spatially complex interdependent networks form an integral component of NI (e.g. energy supply, transport, waste management, clean water supply and dirty water treatment). It is essential that such infrastructure networks and interdependencies can be managed, analysed and modelled in a robust and consistent manner. This paper presents work undertaken to develop a spatial interdependent network model within existing relational database management software that is suitable for national-scale representation of infrastructure network systems and their interdependencies.