Someone like silly code.
the first line is one of the most redundant bits of code I have ever seen. why do you make a subtype of real without setting a range you might as well just leave it at real.
the natural range bit is telling users that the range of this vector, when declared, must be anything from 0 to integer'high. So
signal a: ureal_vector(0 to 10); --valid
signal b: ureal_vector(99 downto 66); --valid
signal c: ureal_vector(-1 to 1); --invalid as -1 is not in the natural range.
But then finally someone is resolving the real type. Is this for some model, maybe of an analogue circuit? this code is not synthesisable.