just store data comment with the post owner id like <'pid>get id tag<'/pid> <'value1>post comment tag<'/value1> <'key1>comments <'key2>get userid tag<'/key2> <'key3>notification<'/key3> so how notification will only be <'key2>var my id tag<'/key> <'key3>notification<'/key3> any activity created with key3 & key2 will save on notification key so key1 can be replace any words or number all tell you somthy happen to u from key1 of som ppl post or comm or vid or img etc