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12.2 Handling of OPC UA Namespaces ToC Previous Next

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 specification shall not use the standard namespaces.

Table 222 provides a list of mandatory and optional namespaces used in a DEXPI 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 a Piping & Instrumentation Diagram represented by the server. This namespace shall have namespace index 1. Mandatory
http://opcfoundation.org/UA/DEXPI/ 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 ObjectTypes defined in this specification or vendor-specific instances of those types 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

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