title: What is the difference between a relational database instance and a relation instance?
body: <p>What's the difference between a <em>relational database instance</em> and a <em>relation instance</em>? What I understand is that a relational database instance is a set of instances, which is a table in a database.  A relation instance is a record or tuple in a table.</p>
  <p>I'm not sure whether my understanding is correct or not. Could anybody tell me the truth please?</p>