I have got an idea, it is simple but it may work. Why don't you hide notification bar as Div tag and design it with css to make it look like notification bar. Then whenever some user likes or comments about the page, write php or js function and connect it to like or comment submit button that will reveal page owners invisible div to visible. And I believe , depending on what you use, I would probably prefer php session() to Identify if page owner is online and can get notifications. moreover, if you need to track statistics of the page, you may create a small database that holds, page id and user comments. You can use this database to push multiple notifications on that hidden Div. you can use Jquery to make it move like Facebook if you want to. I m not %100 percent sure if this is the most optimized way to do that but it is possible. By the way, I surfed some to see what people use to do that. surprisingly I couldn't find something as well.
