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 Nodesmay have the same BrowseName. They are used to build a browse path between two nodes or to define a standard Property.

Serversmay 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 Property. All NodeIdsof Nodesnot defined in this specification shall not use the standard namespaces.

Table 141provides a list of mandatory and optional namespaces used in a DI OPC UAServer.

Table 141– Namespaces used in an OPC UA for Devices Server

NamespaceURI

Description

Use

http://opcfoundation.org/UA/

Namespace for NodeIdsand BrowseNamesdefined in the OPC UA specification. This namespace shall have namespace index 0.

Mandatory

Local Server URI

Namespace for Nodesdefined in the local Server. This may include types and instances used in a Devicerepresented by the Server. This namespace shall have namespace index 1.

Mandatory

http://opcfoundation.org/UA/DI/

Namespace for NodeIdsand BrowseNamesdefined in this specification. The namespace index is Serverspecific.

Mandatory

Vendor specific types and instances

A Servermay provide vendor specific types like types derived from TopologyElementTypeor NetworkTypeor vendor-specific instances of those types in a vendor specific namespace.

Optional

Table 142provides a list of namespaces and their index used for BrowseNamesin this specification. The default namespace of this specification is not listed since all BrowseNameswithout prefix use this default namespace.

Table 142– Namespaces used in this specification

NamespaceURI

Namespace Index

Example

http://opcfoundation.org/UA/

0

0:EngineeringUnits