Notes

Event Structure
activity:
actor : actor performing the activity - "User:20" -> john

verb : defines event type which may be - 'added' 'messages' 'pokes' 'likes' 'followed'

object : object of activity eg- type of activity is follow object is name of company or
followed user / group

target(optional) : target of the activity

foreign_id (optional) : string 'unique attibute for this activity eg, newfollow:5 , new likes:300

time: UTC <-> local time

to: list of user to which activity should be notified (list of channel groups / channel ids)
message : "actual message"

* : any custom attributes

{"actor": "User:1 Joey", "verb": "added", "object": "user: 2 Rachel", " target": "group:1
to group Alumni"};

{"actor": "User:1 John", "verb": "followed", "object": "New Company"};

->aggregation(), main thing we should take care is we should not spam users with notifications, i a user get 10 notifications in a quick time we should aggregate notifi , for eg 'you got 5 new likes'
for a same 'activity'{i mean 'verb'} from multiple 'actor' to single user list 'to'
i don't know what would be in our case


Model and assumptions
Write: Creating events
It should put events to the storage and push to cache like stack for the real time notification to user.And push through pubnub.

Storage: should use NoSql as archive and
users 'x' number of most resent notifications should most probably stored in key:value store in a cache type memory
archive can be like short term memory : rather show 0 notifications than showing (read) notification 1 years old.

Read: cache type memory should be store key value probably like this
user_id ==> Recent Notifications
notificaion id ==> notificaion
backend than handles the received events

Update: Marking as Read/Unread

Push: when event is sent to the user browser should it create push message to phone(in mobile devices) or send email if notification is too important ( eg. your account activity is not safe / you are banned kicked from group)