When analyzing infrastructure it is useful to separate the function from its physical carrier. Water supply is not only a pumping station; it includes power, sources, pumps, distribution, reserves, quality control and repair. Communications are not only a transmitter; they depend on energy, data transport, routing, endpoints and procedures.
Dependency chain
One function may depend on another: water on electricity, communications on electricity and time synchronization, logistics on roads and fuel. A local audit without a dependency map can therefore underestimate systemic risk.