How to draw a diagram defining a map as the composition of two other maps?

Question

I would like to know what is the most common way of drawing a diagram to define a certain map $h: X \to Z$ as the composition of some two mappings: $f : X \to Y$ and $g: Y \to Z$.

Answer 1

You can say

$h$ is defined so that following diagram commutes:

_{(source: presheaf.com)}

which for this simple diagram is precisely the same as saying that $h=gf$.

Answer 2

One possibility is the following:

_{(source: presheaf.com)}