title: Is this design in 5NF?
body: <p>A user can have only one blog (the user owns the blog)<br/>
  Blogs can have multiple posts.<br/>
  Groups can have only one blog (but no particular user owns the blog, it is assumed the group owner created the blog thus userid is only an attribute of user blogs not group blogs so subtyping is needed)<br/></p>
  
  <p><img src="https://i.stack.imgur.com/76Vz5.jpg" alt="enter image description here"></p>
  
  <p>When group_blog_post is deleted, the underlying blog_posts row should be deleted as well, is this best accomplished using a trigger?</p>