Unless you are seeking a representation that you can feed into a computer that understands only very limited mathematics (e.g., it does not understand quantifiers), picking a particular representation is a matter of style. It may be a little ugly, but it's a definition, and in mathematics it is not customary to argue about definitions.
I think that both of your versions are fine. I would probably use the second one because it gives more structure, i.e., it shows that h_a, h_b, j_a, j_b, k_a, k_b are not unrelated numbers but the ends of three intervals. One only needs to consider an interval as an ordered pair, not as a set. Let's denote any ordered sequence of elements by . Then a sample is a quintuple where (is an integer or a real?), , and each of , , and is a pair of some real numbers such that .