Unique Identifier: Email address
If a user is not logged in and accepted cookies – then he will be considered as an anonymous user. you can see in the below diagram (anonId)
If a user is logged-in and accepted cookies- then he will be considered as the Known user and all the previous activities he has done as anonymous user will be tied back to this user. (Please see the highlighted one below, when I logged into my NTO site, IS automatically capture my past history and displayed my email id with the known attribute)
If a user has logged-out and browsing some products on the website- then all his activities will be tied back to the last known user. (You see all the activities has been captured and tied back to my known users)
If a same user is browsing from different systems by logging-in simultaneously/after some time – then IS can able to identify the user and treat as a single user.
If a user cleared the cookies and lands on the website without logging in – then he will be considered as new user.
If a user cleared the cookies and landed on the website by logging in – then he will be considered as known user.