The OPC UA Address Space is a hierarchical structure of Nodes linked by typed References (HasComponent, HasProperty, HasTypeDefinition, etc.), exposed as a graph that clients can walk through the Browse service.

The Address Space is effectively the object filesystem of an OPC UA server. Nodes come in eight NodeClasses (Variable, Object, Method, ObjectType, VariableType, DataType, ReferenceType, View), each identified by a unique NodeId built from a namespace index and an identifier. Nodes are linked by typed References, and human-readable BrowseName/DisplayName attributes make navigation usable. The Browse service lets a client discover the structure dynamically without prior knowledge of the vendor model.

When integrating an unknown server, always Browse before Read: walking References from the Objects folder reveals the real type hierarchy and prevents you from hard-coding NodeIds that the vendor may change at the next firmware release.