"Oliver Elphick" <olly(at)lfix(dot)co(dot)uk> writes:
> I guess I will have to remove the restriction that products listed in
> product_suppliers must be purchased; it may indeed become possible for the
> to change status from time to time, so that is not too unsatisfactory.
You could possibly enforce dependencies like that by using a trigger
function, instead of foreign-key stuff.
regards, tom lane