Corresponds to a value of cdcDGBaseObjectGrpIndex, thus
identifying a set of entries in cdcDGBaseObjectTable, having
this value of cdcDGBaseObjectGrpIndex. This object's value is
used only when cdcDGType is of type 'table'.
This set of entries in cdcDGBaseObjectTable in turn
identifies the set of base objects, that makes up the columns
of this 'table' type data group.
This object's value may be modified at any time. The change
takes effect the next time data is fetched for this data
group.