title: What does this sign "<:" mean in scala?
body: <p>I am going through some scala code. I have come across a sign "&lt;:". What does it mean?</p>
  
  <p>Here is the following code.</p>
  
  <pre><code>abstract class HierarchicalDatabaseObject[TParent &lt;: DatabaseObject](databaseId: String) extends DatabaseObject(databaseId)
  </code></pre>