RDBMS Questions and Answers – Entity Relationship Diagrams

This set of RDBMS Multiple Choice Questions & Answers (MCQs) focuses on “Entity Relationship Diagrams”.

1. Which of the following symbols represent entity sets in an ER diagram?
a) Divided rectangles
b) Diamonds
c) Lines
d) Undivided rectangles

Explanation: Rectangles divided into two parts represent entity sets in an ER diagram. The upper rectangle contains the name of the entity sets. And the lower rectangle contains the attributes.

2. Which of the following symbols represent relationship sets in an ER diagram
a) Divided rectangles
b) Diamonds
c) Lines
d) Undivided rectangles

Explanation: Diamonds represent relationship sets in an ER diagram. Relationship sets define how two entity sets are related in a database.

3. What do double diamonds represent in an ER diagram
a) They link entity sets to relationship sets
b) Total participation of an entity in a relationship set
c) Relationship sets linked to weak entity sets
d) None of the mentioned

Explanation: The double diamonds represent the relationship sets linked to weak entity sets. Weak entity sets are the sets that do not have a primary key.

4. What does a directed line ( → ) from a relationship set to two entity sets mean?
a) One-one
b) Many-one
c) Many-many
d) One-many

Explanation: A directed line ( → ) from a relationship set to two entity sets means that there is a one-one cardinality between two entity sets.

5. How are roles specified in an ER diagram
a) By labelling the rectangles
b) By labelling the diamonds
c) Roles cannot be specified in an ER diagram
d) By labelling the lines

Answer: E-R diagrams can include role indicators. Roles can be specified in an ER diagram by labelling the lines.
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6. How is the discriminator of a weak entity set specified?
a) Using a solid line
b) Circling it
c) Using a dashed line
d) Drawing a square around it

Explanation: A discriminator of a weak entity set can be specified by underlining it with a dashed line.

7. An entity set that has a primary key is called as ___________
a) Strong entity set
b) Weak entity set
c) Complete entity set
d) None of the mentioned

Explanation: An entity set that has a primary key is called as a strong entity set. An entity set that does not have a primary key is called a weak entity set.

8. The relationship associating the weak entity sets with the identifying entity set is called as ________
a) Identifying relationship
b) Connecting relationship
c) Completing relationship
d) Unique relationship

Explanation: The relationship associating the weak entity sets with the identifying entity set is called as an Identifying relationship. An identifying set is a many to one from the weak entity set to the identifying entity set.

9. State true or false: Every weak entity set must be associated with an identifying entity
a) True
b) False

Explanation: Every weak entity set must be associated with an identifying entity. The weak entity is then said to be existence dependent on the identifying entity set.

10. State true or false: A weak entity can participate in all the relationships.
a) True
b) False

Explanation: It cannot participate in all the relationships. A weak entity set can only participate in relationships other than the identifying relationship.

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