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 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 document shall not use the standard namespaces.
Table 6 provides a list of mandatory and optional namespaces used in an OPC 40084-4 OPC UA Server.
Table 6 – Namespaces used in an OPC 40084-4 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 a device represented by the server. This namespace shall have namespace index 1. |
Mandatory |
|
Namespace for NodeIds and BrowseNames defined in OPC UA Part 100. The namespace index is server specific. |
Mandatory |
|
|
http://opcfoundation.org/UA/PlasticsRubber/ GeneralTypes/ |
Namespace for NodeIds and BrowseNames defined in OPC 40083. The namespace index is server specific. |
Mandatory |
|
http://opcfoundation.org/UA/PlasticsRubber/ Extrusion/GeneralTypes/ |
Namespace for NodeIds and BrowseNames defined in OPC 40084-1. The namespace index is server specific. |
Mandatory |
|
http://opcfoundation.org/UA/PlasticsRubber/ Extrusion/HaulOff/ |
Namespace for NodeIds and BrowseNames defined in this specification. The namespace index is server specific. |
Mandatory |
|
Vendor specific types and instances |
A server may provide vendor specific types like types derived from MachineType or MachineStatusType or vendor specific instances of devices in a vendor specific namespace. |
Optional |
Table 7 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 7 – Namespaces used in this specification
|
NamespaceURI |
Namespace Index |
Example |
|
0 |
0:NodeVersion |
|
|
2 |
2:DeviceClass |
|
|
3 |
3:MachineInformationType |
|
|
http://opcfoundation.org/UA/PlasticsRubber/Extrusion/GeneralTypes/ |
4 |
4:ExtrusionDeviceType |