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The AddressSpace is modelled as a set of Nodes accessible by Clients using OPC UA Services (interfaces and methods). Nodes in the AddressSpace are used to represent real objects, their definitions and their References to each other.

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.

A View is a subset of the AddressSpace. Views are used to restrict the Nodes that the Server makes visible to the Client, thus restricting the size of the AddressSpace for the Service requests submitted by the Client. The default View is the entire AddressSpace. Servers may optionally define other Views. Views hide some of the Nodes or References in the AddressSpace. Views are visible via the AddressSpace and Clients are able to browse Views to determine their structure. Views are often hierarchies, which are easier for Clients to navigate and represent in a tree.

The OPC UA AddressSpace supports information models. This support is provided through:

1. Node References that allow Objects in the AddressSpace to be related to each other.
2. ObjectType Nodes that provide semantic information for real Objects (type definitions).
3. ObjectType Nodes to support subclassing of type definitions.
4. Data type definitions exposed in the AddressSpace that allow industry specific data types to be used.
5. OPC UA companion standards that permit industry groups to define how their specific information models are to be represented in Server AddressSpace.