How to script conditions for a selection from a selection?

[#1]

Basically, ive got a massive dataset.

currently making the ui and the way the application is going to work is thta the user is going to be passed through a linear route to the end graphs ect.

so.

there are going to be buttons to the next page ect but i only want them to be enabled if the user has selected something

on the next page there is goign to be a graph, then i want another graph to appear under the graph once the user has selected a region of the graph.

is there any way to acheive this?

thank you in advance

Rhys Bradbury

[#2]

i guess what im asking is that is there a system var which stores the users current selection... there must be ??