net weaver ume

hello:

i am studying net weaver 's ume.I have had conception of action.xml,etc.

i have a question:

how to display view according user 's Authentication.

<i>more info:</i>

I will write a calculator program,it has two operations:"add","sub"

i have created three users,

user A can use "add",

user B can use "sub",

user C can use two operations,

when user A logon to web,he only see url of "add",

when user B logon to web,he only see url of "sub",

when user C logon to web,he can see two url.

how can i implement this program?