Plot x1 ,x2,y

Hi
I have a question.
I have 3 series of data. I want to use a graph for each point that containing 3 values (x1,x2,y).
I want to define x2 axis on top of the graph,and x1 on the bottom . x1 should be start from right and x2 from left.
Can anyone help me please ?

How do you have 3 values (x1,x2,y) in a 2-dimensional graph? Please explain in typical mathematical terms (x axis is horizontal, y axis is vertical).