Numerous HMI/SCADA applications contain their own tag databases which eliminate the need to define tags within an OPC Server (used heavily in COM Classic). Naturally, this requires the OPC Server to define a special tag-name syntax that will allow it to dynamically add the tag to the address-space.

I'm thinking about how HMI vendors migrate towards UA, and how important this existing feature (described above) for COM Classic users, and how the HMI vendor can incorporate something similar.

An example would be: in my HMI tag database I've defined a tag called "temp1" is mapped to a Modbus address of "40001". I want to use AddNodes to define this within the address-space, and while I can define all aspects of the node (name, browse name, data-type, EU range etc.) I cannot specify some kind of underlying source (the modbus address).

I looked in Part 8 to see if something is available there and didn't see anything. So I wonder if we should add something to describe an "underlying address" (or other name).

I realize that this may be covered in a companion spec; but I wonder if this should be covered as part of the DA spec since it's most likely the DA clients (HMIs mostly) that would probably use this feature.

One thought would be to allow those vendors that have this capability in COM Classic to simply extend their custom tag-name syntax to the NodeId. But that doesn't seem too clean when we have this AddNodes/AddReferences capability.

I'm fishing for feedback/thoughts as I am preparing compliance for these services. Thanks.