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Node with NodeClass 'Variable' but without a valid DataType
May 23, 2024
17:05, EEST
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rocket science
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Hi there,

I’ve observed something strange with an OpcUa server.

On this server there is a node, which has a NodeClass Variable, but when I look at the DataType, it shows me:

v DataType
….> NamespaceIndex 0
….> NamespaceURI http://opcfoundation.org/UA/
….> IdentifierType 0 (Numeric)
….> Identifier 0

When checking the Types, there is no Type with NodeId 0 in Namespace 0. Is this something which is valid?

Thanks!

May 24, 2024
9:21, EEST
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Matti Siponen
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Hello,

A NodeId with NamespaceIndex 0 and Numeric value 0 is a null NodeId. It doesn’t (or at least it shouldn’t) refer to any Node in the Server’s AddressSpace.

A Server returning such NodeId for a DataType Attribute of a Variable means that the Server doesn’t specify the DataType for that Variable. The OPC UA Specification states that the DataType Attribute shall be a valid non-null NodeId (https://reference.opcfoundation.org/Core/Part3/v105/docs/5.6), but we have seen Servers return null NodeId for DataType Attribute before.

May 24, 2024
10:08, EEST
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rocket science
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Thank you for clarification!

May 24, 2024
12:14, EEST
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Is there any possibility to create such a Variable with a null NodeId as DataType (just for testing porposes) using the Prosys Server SDK?

May 24, 2024
12:34, EEST
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Matti Siponen
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Hello,

Yes, it is possible to set value of the DataType Attribute of a Variable Node to null NodeId in the SDK.

If the Variable is UaVariableNode, you can use the setDataTypeId(NodeId) method to set its DataType to null NodeId (which is NodeId.NULL in the SDK). In the MyNodeManager of SampleConsoleServer, you could use that method to set the DataType to null NodeId for MySwitch and/or MyLevel.

If your NodeManager doesn’t use UaNodes, you can configure the readAttribute(NodeId, UnsignedInteger, NumericRange, DateTime) of your IoManager or the onReadNonValue(ServiceContext, NodeId, UaNode, UnsignedInteger, DataValue) method of your IoManagerListener to return null NodeId as the value of DataType for some Variable Node or Nodes. In MyBigNodeManager of SampleConsoleServer, you could modify the onReadNonValue method of the MyBigIoManager to always return null NodeId for the DataType Attribute.

June 4, 2024
10:50, EEST
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Thanks!

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