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 13 provides a list of mandatory and optional namespaces used in an Sercos OPC UA Server.
Table 13– Namespaces used in a Sercos Server
|
Namespace |
Description |
Use |
|
Namespace for NodeIds and BrowseNames defined in the OPC UA specification. This namespace shall have namespace index 0. |
Mandatory |
|
|
Namespace for NodeIds and BrowseNames defined in Sercos. The namespace index is server specific. |
Mandatory |
|
|
Vendor specific types and instances |
A server may provide vendor specific types or vendor specific instances of devices in a vendor specific namespace. |
Mandatory |