Namespaces are used by OPC UA to create unique identifiers across different naming authorities. The Attributes NodeId and BrowseName are identifiers. A Node in the UA AddressSpace is unambiguously identified using a NodeId. Unlike NodeIds, the BrowseName cannot be used to unambiguously identify a Node. Different Nodes may have the same BrowseName. They are used to build a browse path between two Nodes or to define a standard Property.
Servers may often choose to use the same namespace for the NodeId and the BrowseName. However, if they want to provide a standard Property, its BrowseName must have the namespace of the standards body although the namespace of the NodeId reflects something else, for example the EngineeringUnits Property. All NodeIds of Nodes not defined in this document must not use the standard namespaces.
[RQ12.1] Table 43 provides a list of mandatory and optional namespaces used in a OPC UA server according to this document.
Table 43 – Namespaces used in a Safety Server
|
NamespaceURI |
Description |
Use |
|
Namespace for NodeIds and BrowseNames defined in the OPC UA specification. This namespace shall have namespace index 0. |
Mandatory |
|
|
Local Server URI |
Namespace for nodes defined in the local server. This may include types and instances used in an AutoID Device represented by the Server. This namespace shall have namespace index 1. |
Mandatory |
|
Namespace for NodeIds and BrowseNames defined in this document. The namespace index is Server specific. |
Mandatory |
|
|
Vendor-specific types |
A Server may provide vendor-specific types like types derived from ObjectTypes defined in this document in a vendor-specific namespace. |
Optional |
|
Vendor-specific instances |
A Server provides vendor-specific instances of the standard types or vendor-specific instances of vendor-specific types in a vendor-specific namespace. It is recommended to separate vendor-specific types and vendor-specific instances into two or more namespaces. |
Mandatory |