OPC-UA server with multiple nodes using eclipse milo

Question

I am building a OPC-UA server using eclipse milo. What are the different ways to provide multiple nodes for a subscription service? Can I define a custom data object having properties of basic data types, for this? How?

I want to have a service which serves data of different data types (Integer, Double, Boolean etc.) as it's output. Each of the values should be named different not single name like array output with single name for all of the values. For this purpose is there a way to define a custom data object class with attributes of different types? Is this possible in OPC to have a custom data object type as output of a service?

Answer 1

Conceptually, adding Nodes with each of the different DataTypes you're asking about is no different than creating a folder node and adding nodes to that.

The ExampleNamespace in the milo-examples project shows you how to do that.

If you truly want to use an instance of a custom ObjectType rather than an instance of FolderType then there's a bit of bookkeeping work you'll need to do.

1. Create an instance of ObjectTypeNode to describe your new type.
2. For each property/member it will have, create a new VariableNode with that configured with the DataType you want, then add a HasComponent or HasProperty reference from your ObjectTypeNode to this VariableNode. (These Nodes are what the spec calls InstanceDeclarations)
3. Add your ObjectTypeNode to the address space as a subtype of BaseObjectTypeNode.

Then, when you created your original ObjectNode, you'd specify the type definition as being your newly created ObjectTypeNode rather than, say, a FolderType.

You can get a better idea about how all this works in Part 3 and 5 of the spec or by using a client like UaExpert to inspect some of the pre-existing ObjectTypes in the server, such as ServerType.

Edit: There's now an example of how to do this here. If this seems a bit bulky... you're right. Typically ObjectTypes and VariableTypes are designed in a modelling tool and imported via a NodeSet XML file, but that's outside the scope of things right now...