如何更新从网站发送的FB通知？

Sending notification now is pretty easy. I have fallowed the dev docs here and done that.

I was wondering if it is possible to check if user has seen it and if not then overwrite it.

For example - I notify user that new product that might be of interest for him has been added to my database. I do it almost real-time. Now if 5 products are added within one hour user would get 5 fb notifications which would be pretty anoying experience for him. Much better user experience would be if he would get one notification saying that 5 products has been added.

When sending notifications I can add ref parameters that is used to group my notifications.

1. Is there a way to query the fb api before sending notification if user with given fbid has seen notification with given ref parameter?
2. Is there a way to overwrite (I guess delete last and send new updated one) notification if he has not seen it?

I am using PHP SDK v5.

Notifications can only be sent, you cannot access them after that in any way. There is no API for it.

1. No
2. No