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Part 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.

Part 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.