title: Facebook "like" data structure
body: <p>I've been wondering how facebook manages the database design for all the different things that you can "like". If there is only one thing to like, this is simple, just a foreign key to what you like and a foreign key to who you are.</p>
  
  <p>But there must be hundreds of different tables that you can "like" on facebook. How do they store the likes?</p>