[Roboprog]

I hear you on the education thing. Intuitively, the "two tables with same structure" approach is redundant, but it's helpful to have the math/logic to unambiguously define what "redundant" is.

Having 2 tuple types with 3 values seems harmless. This explodes quickly when done with many columns or many tables. Having some kind of foreign key to act as a "discriminator" scales much better to constrain the number of value types (# of tables x # of columns) that must exist.

But I only say this because of having to deal with a legacy DB at work that violates the Hell out of this :-)

... which brings us full circle to the tragedy of a lack of education.