Analogy
We have separated this cupcake into multiple parts the parts are...
-Whole cupcake
-Icing
-Toppings
-Whole cupcake
-Icing
-Toppings
Whole cupcake
The whole cupcake would represent the biography and the autobiography because it talks about the person as a whole as is the whole cupcake.
Icing
Icing would represent a memoir since it is only one part of a cupcake and is not a story of a person's whole life as which it would be a whole cupcake.
Toppings
The toppings represent personal narratives and diaries. They represent toppings because personal narratives and diaries aren't too long as compared to a biography or memoir