Implementing notifications

What is the simplest way to implement notifications?

Like if a user through a web app is listening to some contract events and wants to be notified of only the new ones?

I have live query working but I am not sure how to only show new ones that were never seen before.

Presumably I would have to send a read statements to a field on the database?

if you know when a message is read, you could update the database with that information and you would know not to show it next time