title: Notifications like facebook - What's in the URL field?
body: <p>I am implementing a facebook like notifications system in my application.
  My notifications table contains following fields</p>
  
  <pre><code>source_id (User_id)
  Type (ENUM - type of notification, eg: like,comment,new post, etc)
  description (some description)
  URL (the destination URL)
  created_on 
  </code></pre>
  
  <p>How I would work with the notifications is decided. But what I am thinking is, 
  What exactly the URL column here would contain? If I put an absolute URL for a post like</p>
  
  <pre><code>http://facebook.com/thomas/posts/123456
  </code></pre>
  
  <p>Wouldn't this be a problem? What if the user changes its username from <strong>thomas</strong> to something else tomorrow?
  Just needed help in how can I work with destination URL, either on frontend (I'm using PHP) or backend (in database column itself)</p>