Enterprise Portal SSO mechanism

Hi

I have some very basic quesiton's about SSO. Let's say we have implemented SSO with SAP logon tickets (EP--> ECC).

Now let's say the business user log-on's to EP and try's to access iview which fethches data from ECC and display's it.

Now my questions are

1. Since we have implemented SSO, the business user need not to have userid/password physically in ECC ?

2. Is it sufficient to have just EP userid/password to acces iview which fetches data from ECC ?

3. If I am not wrong, at communicaiton layer "certificate authenticaiton" works as "System User" to access ECC and fetch data ?

Please advise.

Thanks

Ravindra