16. Suppose a book author can be identified by an AuthorID and each book can be

Question

16. Suppose a book author can be identified by an AuthorID and each book can be identified by an ISBN. Besides the identifier, an author and a book each has many other attributes like name, address, email, phone, and price, title, publisher, publish year, edition, etc. In general publishing business, an author may write no book or many books but every book must have at least one author.

If a data model is defined for the above business in an entity-relationship diagram (ERD) as shown below. Then, which multiplicity symbol should be used at the place pointed by the red arrow?

17. If we continue on Question 16 to complete the ERD of the data model, which multiplicity symbol should be used at the place pointed by the blue arrow?

18. If the data model of Question 16 and 17 is revised to replace the many-to-many relationship, a new entity, say, Contract, must be included in between Author and Book and the many-to-many relationship will be replaced by two new relationships as shown below. Then, the multiplicity at the place pointed by the red and blue arrows should be

b. at the red arrow and (d) at the blue arrow

c. at the red arrow and (a) at the blue arrow

a.  at the red arrow and (d) at the blue arrow

d. at the red arrow and (c) at the blue arrow

19. If the Contract entity of the ERD shown in Question 18 is implemented as a table in database, how many foreign keys it will have?

a. zero

b. one

c. two

d. three

Explanation / Answer

Answer is as follows:

a) We know that atleast one or more author writes a book.

Symbol to indicate one or more is (B)

So the correct option is B

b) We know that zero to multiple books are written by any author.

Symbol to indicate zero or more is (A)

So the correct option is A

c) The fourth option is correct if we replace by many to many relationship and generate a new entity.

So the relationship betweem author and contract is one to many. So we know that there is atleast one author that represent in symbol d and books has atleast 0 that represent in symbol c.

So Fourth Option is correct d at blue side and c at red side.

d) There are two forirgn keys in table Contract one is from AuthorId and other is ISBN.

So correcct option is C

if there is any query please ask in comments.....

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