title: How are ER modeled subtypes implemented in the database?
body: <p>Sorry if this is too simple, but I've found a lot of documentation on ER-modeling recently, but all of it seems to skip over the actual implementation and I just want to clarify.</p>
  
  <p>Is a subtype just a second table with a foreign key to the supertype along with the properties belonging to the subtype?  This is what would make most sense to me, anyhow.  The primary key of the subtype would typically be shared with the supertype also (primary of subtype has foreign constraint on supertype)?</p>