10.2 Handling of OPC UA Namespaces
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 0:EngineeringUnits Property. All NodeIds of Nodes not defined in this document shall not use the standard namespaces.
Table 157 provides a list of mandatory and optional namespaces used in a Pumps and Vacuum Pumps OPC UA Server.
| NamespaceURI | Description | Use |
| http://opcfoundation.org/UA/ | 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 |
| http://opcfoundation.org/UA/DI/ | Namespace for NodeIds and BrowseNames defined in OPC 10000-100. The namespace index is Server specific. | Mandatory |
| http://opcfoundation.org/UA/Machinery/ | Namespace for NodeIds and BrowseNames defined in this document. The namespace index is Server specific. | Mandatory |
| http://opcfoundation.org/UA/Pumps/ | 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 |
Table 158 provides a list of namespaces and their index used for BrowseNames in this document. The default namespace of this document is not listed since all BrowseNames without prefix use this default namespace.
| NamespaceURI | Namespace Index | Example |
| http://opcfoundation.org/UA/ | 0 | 0:EngineeringUnit |
| http://opcfoundation.org/UA/DI/ | 2 | 2:DeviceRevision |
| http://opcfoundation.org/UA/Machinery/ | 3 | 3:Location |