"cannot create column or table of type that contains a supertype attribute"
*Cause: The user tried to create a column or table of an object type that
contains a supertype attribute. This is not supported because
it leads to infinite recursion in our current storage model.
Note that creating a column of a type implies that we
create columns corresponding to all subtype attributes as well.
*Action: Change the type definition to contain a supertype REF attribute
instead of the supertype object attribute.