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

Question

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?

Question 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?

Question 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

Question 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?

Explanation / Answer

Question 16:

Correct option: (b)

Explanation:

Every book must have at least one author; so multiplicity will be one or more and that symbol is given in b.

Question 17:

Correct option: (a)

Explanation:

An author may write no book or many books so multiplicity will be zero or more and that symbol is given in a.

Question 18:

Correct option: (a) at the red arrow and (d) at the blue arrow

Explanation:

The relationship between author and contract is zero to many and relationship between book and contract is one and only one. Because one author may have zero contract or many contracts but one book will be associated with only one contract ; the symbol of zero or many is given in a and symbol of one and only one is given in d; hence the correct option is (a) at the red arrow and (d) at the blue arrow.

Question 19:

Correct option: (c) two

Explanation:

There are two foreign keys in table Contract one is AuthorId and other is ISBN.

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