$1.$ What is an entity supertype, and why is it used?

$2.$ Describe what is meant by a specialisation hierarchy?

$3.$ What is a subtype discriminator? Given an example of its use.

$4.$ What is an overlapping subtype? Give an example.

$5.$ What is a disjoint subtype? Give an example

$6.$ What is the difference between partial completeness and total completeness?