Namespaces are used by OPC UA to create unique identifiers across different naming authorities. The Attributes NodeIdand BrowseNameare identifiers. A node in the UA Address Spaceis unambiguously identified using a NodeId. Unlike NodeIds, the BrowseNamecannot 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 NodeIdand the BrowseName. However, if they want to provide a standard Property, its BrowseNameshall have the namespace of the standards body although the namespace of the NodeIdreflects something else, for example the EngineeringUnits propery. All NodeIdsof nodes not defined in this specification shall not use the standard namespaces.

Table 131provides a list of mandatory and optional namespaces used in an AutomationML OPC UAServer.

Table 131– Namespaces used in a AutomationML Server

Namespace

Description

Use

http://opcfoundation.org/UA/

Namespace for NodeIdsand BrowsNamesdefined 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

http://opcfoundation.org/UA/AML/

Namespace for NodeIdsand BrowseNamesdefined in AutomationML. The namespace index is server specific.

Mandatory

http://opcfoundation.org/UA/AML/AMLLibs/

Namespace for NodeIdsand BrowseNamesdefined in AutomationML libraries. The namespace index is server specific.

Optional