20. When a one-to-one relationship in E-R model is mapped into relational data m
ID: 3553313 • Letter: 2
Question
20. When a one-to-one relationship in E-R model is mapped into relational data model, the one-to-one relationship is generally represented as
a. a primary key.
b. a foreign key.
c. a primary key in one table and a foreign key in another table or the same table of the primary key.
d. a table with a pair of foreign keys, each of which is associated to a primary key in its parent table.
21. When a one-to-many relationship in E-R model is mapped into relational data model, the one-to-many relationship is generally represented as
a. a primary key.
b. a foreign key.
c. a primary key in one table and a foreign key in another table or the same table of the primary key.
d. a table with a pair of foreign keys, each of which is associated to a primary key in its parent table.
22. When a many-to-many relationship in E-R model is mapped into relational data model, the many-to-many relationship is generally represented as
a. a primary key.
b. a foreign key.
c. a primary key in one table and a foreign key in another table or the same table of the primary key.
d. a table with a pair of foreign keys, each of which is associated to a primary key in its parent table.
Explanation / Answer
1) c
The primary key of one entity type comes the foreign key in the other
2) d
in 1-m relationships
The primary key from the `one side' is placed as a foreign key in the `many side'.
3) d
in many to many relationship
A new relation is produced which contains the primary keys from both sides of the relationship
These primary keys form a composite primary key.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.