Glossary · Industrial communication
OPC UA address space
Also known as: Address space (OPC UA)
German: OPC-UA-Adressraum
In OPC UA, the address space is the set of nodes that a server makes visible to clients, where each node belongs to one of eight node classes (Object, Variable, Method, ObjectType, VariableType, ReferenceType, DataType, View), is identified by a NodeId within a namespace, and is linked to other nodes by typed references.
- Industrial communication
- Standards
In one sentence
The OPC UA address space is the network of nodes, node classes, references and namespaces through which a server exposes its information.
Example
In a labeler's address space, the object Labeler1 is of a MachineType from a companion specification, has variables for state and label count and a method StartJob, and references its two print head objects.
How it applies
- Engineering: References make the address space a graph, not just a tree: hierarchical references (such as HasComponent) give the browse structure, non-hierarchical ones (such as HasTypeDefinition) link instances to their types. Types let clients recognize the same kind of machine on any server.
- Namespaces: Every NodeId carries a namespace index that points into the server's namespace array of URIs. The index can differ between servers and restarts, so integrations store the namespace URI, not the index.
- Modeling: Address spaces are designed as Information models and exchanged as OPC UA NodeSet files. Companion specifications add industry-specific types.
- Documentation: The documentation team documents the namespace URIs, the object structure, the meaning, units and ranges of variables, the methods with their arguments and effects, and the events.
Address space vs. information model
The information model defines types and rules; the address space is what one server actually exposes, instances included. The protocol vs. data model distinction applies: the services move data, the address space gives it structure and meaning.