The following data model was created as part of a library reservation system. Which of the statements below is correct? Here, a pair of 1 and an asterisk shows the one-to-many cardinality and the underlined attributes in the table are primary keys.
[Data Model of Reservation System]
User (User_ID, User_ name, Address)
Reservation (User_ID, Book_title_ID, Reservation_date)
Book_title (Book_title_ID, Category_code, Book_name, Author)
Book-stocked (Book_stock_ID, Book_title_ID, Purchase_date, Lending_count)
a) The cardinality between the book_title entity and the book_stocked entity is opposite.
b) It is redundant to categorize the book_title entity and the book_stocked entity separately.
c) The book_title entity is an abstract entity without a physical entity.
d) The book stocked to be lent out can be decided at the time of reservation.