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 Address Space 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 shall 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 specification shall not use the standard namespaces.
Table 55 provides a list of mandatory and optional namespaces used in a POWERLINK OPC UA Server.
Table 55 – Namespaces used in a POWERLINK OPC UA Server
|
Namespace |
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 a device represented by the server. This namespace shall have namespace index 1 in the server. |
Mandatory |
|
Namespace for NodeIds and BrowseNames defined in OPC 10000-100. The namespace index is server specific. |
Mandatory |
|
|
Namespace for NodeIds and BrowseNames defined in this specification. The namespace index is server specific. |
Mandatory |
|
|
Namespace for NodeId scheme defined in paragraph 8. The namespace index is server specific. |
Optional |
|
|
Vendor specific types and instances |
A server may provide vendor specific types like types derived from PowerlinkDeviceType or PowerlinkCnConnectionPointType, or vendor specific instances of devices in a vendor specific namespace. |
Optional |
Table 56 provides a list of namespaces and their index used for BrowseNames in this specification. The default namespace of this specification is not listed since all BrowseNames without prefix use this default namespace.
Table 56 – Namespaces used in this specification
|
Namespace |
Namespace Index |
Example |
|
0 |
0:EngineeringUnits |
|
|
1 |
1:SerialNumber |