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 property. All NodeIdsof nodes not defined in this specification shall not use the standard namespaces.

Table 55provides a list of mandatory and optional namespaces used in a POWERLINK OPC UAServer.

Table 55– Namespaces used in a POWERLINK OPC UA Server

Namespace

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 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 in the server.

Mandatory

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

Namespace for NodeIdsand BrowseNamesdefined in OPC 10000-100. The namespace index is server specific.

Mandatory

http://opcfoundation.org/UA/POWERLINK/

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

Mandatory

http://opcfoundation.org/UA/POWERLINK/DirectAccess/

Namespace for NodeId schemedefined in paragraph 8. The namespace index is server specific.

Optional

Vendor specific types and instances

A server may provide vendor specific types like types derived from PowerlinkDeviceTypeor PowerlinkCnConnectionPointType,or vendor specific instances of devices in a vendor specific namespace.

Optional

Table 56provides a list of namespaces and their index used for BrowseNames in this specification. The default namespace of this specification is not listed since all BrowseNames without prefix use this default namespace.

Table 56– Namespaces used in this specification

Namespace

Namespace Index

Example

http://opcfoundation.org/UA/

0

0:EngineeringUnits

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

1

1:SerialNumber