title: Database structure, trying to find primary keys
body: <p>I have a database with the following tables, Member, Paper, Topic, Interest, Associated.</p>
  
  <p>I need a member to register than upload a paper. When they register they state their interests and this should appear on their home screen. </p>
  
  <p>However in my tables interest i have member_id and topic_id, do i need a primary key for this table? As both of those are foreign keys. And with associated i have paper_id and topic_id but again i have no clue as to what the primary keys should be in those tables. </p>