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OPC-UA Browse Service

Browse node paths

The Browse Service functionality of the Edge Xpert device service searches for OPC-UA nodes along a specified path.

An example of a node path could be: 

Objects/Device/Node
In this example, Objects has a browse depth of 1, Device has a browse depth of 2, and Node has a browse depth of 3.

Browsing nodes to add subscriptions

To enable the Browse service, you must specify the following protocol properties when provisioning a device:

Property Description Example Value
BrowseDepth The BrowseDepth must be greater than zero (0). This protocol property limits the depth to which the node tree is browsed. If set to 1, browsing stops after the initial browse. If set to a value greater than 1, the children of RootNode are also browsed, and this continues until the namespace has been browsed to the maximum BrowseDepth level. 2
RootNode When initiated, the browse starts from the RootNode. The format for this value must be < nsIndex>,< IDType>=< nodeID> 3,i=1001

This would indicate a node with a Namespace Index (or nsIndex) of 3, a numeric ID type (indicated by the "i") and a node ID of 1001

Optionally, the BrowseSubFilter protocol property can be used to automatically subscribe to nodes of interest. This can take the following values:

  • All
  • Variable
  • Event

Note

If automatically subscribing to browsed nodes, the performance of the OPC-UA Device Service can be impacted when there are a lot of subscription events (e.g., if automatically subscribing to nodes on servers with large namespaces). If the OPC-UA Device Service has multiple connections to the same OPC-UA server, IOTech recommends that the Browse service is enabled on only one connection to prevent duplication and unnecessary overhead.

Adding a node without knowing the nodeID

Browse can be used to declare objects in a device profile without specifying the nodeID for a node. This can be implemented when using multiple devices and allows device profiles to be more general. It is not necessary to know the nodeID of individual nodes, so long as the starting node is known.

By specifying the browse path and starting node, the device service knows where to look for nodes and will add all nodes on the path that are defined in the device profile.

To use this feature, two new attributes must be added to the device resource.

Attribute Description Example
browsePath Path from the root node to the node browsePath: "Simulation/Counter"
startNode Information on the root node. Must contain the namespace index (nsIndex), ID type, and node ID

The format for this must be < nsIndex>,< IDType>=< nodeID>		 startNode: "0,i=85"

This indicates a nsIndex of 0, numeric ID type ("i"), and node ID of 85

An example device profile for using the browse path to find nodes in the Prosys OPC-UA Simulation Server can be seen below:

deviceResources:

 - description: A Simulated Counter
   name: Counter1
   isHidden: false
   properties:
     valueType: Uint32
     readWrite: R
     units: String
     defaultValue: "0"
   attributes:
     browsePath: "Simulation/Counter"
     monitored: "True"
     nsIndex: "3"
     publishInterval: "500"
     startNode: "0,i=85"
 - description: A static UInt32 variable
   name: StaticUInt32
   isHidden: false
   properties:
     valueType: Uint32
     readWrite: RW
     units: String
     defaultValue: "0"
   attributes:
     browsePath: "StaticData/StaticVariables/UInt32"
     nsIndex: "5"
     startNode: "0,i=85"
deviceCommands:
  - name: Counter1
    isHidden: false
    readWrite: R
    resourceOperations:
      - deviceResource: Counter1
  - name: StaticUInt32
    isHidden: false
    readWrite: RW
    resourceOperations:
      - deviceResource: StaticUInt32
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