Union data

A (tagged) union contains a single value out of several possible fields (or no value at all). It is represented by an instance UnionData Class.

In data type dictionary model (the only model before OPC UA 1.04), union data is not directly available. A union can, however, be quite efficiently modeled using an appropriately formed structure with optional fields.

The string FieldName Property contain the name of the field currently contained in the union (this is the "tag" of the union). An empty string in this property denotes a union that currently contains no data.

The FieldValue Property contains the value of the field currently selected in the union.