Consider the E-R diagram in Figure given below, which models an online bookstore.
a. List the entity sets and their primary keys.
b. Suppose the bookstore adds Blu-ray discs and downloadable videos
to its collection. The same item may be present in one or both formats,
with differing prices. Extend the E-R diagram to model this addition,
ignoring the effect on shopping baskets.
c. Now extend the E-R diagram, using generalization, to model the case
where a shopping basket may contain any combination of books,
Blu-ray discs, or downloadable video.
