OPC 10000-3 contains the details of the meta model “building blocks” used to create an AddressSpace out of interconnected Nodes in a consistent manner. Servers are free to organize their Nodes within the AddressSpace as they choose. The use of References between Nodes permits Servers to organize the AddressSpace into hierarchies, a full mesh network of Nodes, or any possible mix.
OPC 10000-5 defines OPC UA Nodes and References and their expected organization in the AddressSpace. Some Profiles will not require that all of the UA Nodes be implemented.