Namespaces are used by OPC UA to create unique identifiers across different naming authorities. The Attributes NodeIdand BrowseNameare identifiers. A Nodein the UA AddressSpaceis unambiguously identified using a NodeId. Unlike NodeIds, the BrowseNamecannot be used to unambiguously identify a Node. Different Nodesmay have the same BrowseName. They are used to build a browse path between two Nodesor to define a standard Property.
Serversmay often choose to use the same namespace for the NodeIdand the BrowseName. However, if they want to provide a standard Property, its BrowseNamemust have the namespace of the standards body although the namespace of the NodeIdreflects something else, for example the EngineeringUnits Property. All NodeIdsof Nodesnot defined in this part must not use the standard namespaces.
[RQ13.1] Table 34provides a list of mandatory and optional namespaces used in a Safety OPC UAServer.
Table 34– Namespaces used in a Safety Server
|
NamespaceURI |
Description |
Use |
|
Namespace for NodeIdsand BrowseNamesdefined 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 NodeIdsand BrowseNamesdefined in this part. The namespace index is Serverspecific. |
Mandatory |
|
|
Vendor specific types |
A Servermay provide vendor-specific types like types derived from ObjectTypes defined in this part in a vendor-specific namespace. |
Optional |
|
Vendor specific instances |
A Serverprovides 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 |