> Ideally, I should be able to declare a "platonic" Story that includes
> all fields that describe a story.  A Full story is just the real-world
> clone of the platonic ideal, while a Blurb is a Story with the constraint
> that there is no "body" field declared (and so on).
>   
That seems backwards from the way OO inheritance is supposed to work.  
You don't go from a more feature-rich case to a less feature-rich case 
-- it's the other way around.

If you s/blurb/header/g or s/blurb/summary/g, then a Full story arguably 
is-a blurb with a body tacked on.

~~ Robert.