[Not sure if Part 3 or Part 5 issue. Maybe both.]

Motivation in detail: See attached PDF.

In a nutshell: It is desirable to restrict a rather generic structured DataType, e.g. for fields to limit the array size, define concrete data types, to leave out optional fields, to require optional fields etc. In addition, this also allows adding additional metadata like the EngineeringUnit on a specific field.

Related: Sometimes the refinement of a DataType (in a field, but also directly on a variable) is not to one concrete DataType, but several. For example, a Variable of Numeric only allows Int32 or UInt32. This should be solved for fields and Variables in general.

The PDF also sketches a possible solution, but no details.

Initially discussed in UA WG Meeting 2025-03-04