Entity Relationships

Question 1

What is an entity

Answer 1

• An entity may be any object, class, person or place.
• In the ER diagram, an entity can be represented as rectangles.
• Consider an organization as an example- manager, product,
employee, department etc. can be taken as an entity.

Question 2

What is weak entity

Answer 2

a. Weak Entity
• An entity that depends on another entity called a weak entity.
• The weak entity doesn’t contain any key attribute of its own.
• The weak entity is represented by a double rectangle.

Question 3

Describe attributes

Answer 3

The attribute is used to describe the property of an entity.
• Eclipse is used to represent an attribute.
• For example, id, age, contact number, name, etc. can be
attributes of a student.

Question 4

Mention types of attributes

Answer 4

Key attribute
Composite
Multivalued

Question 5

Describe key attributes

Answer 5

a. Key Attribute
• The key attribute is used to represent the main characteristics of an entity.
• It represents a primary key.
• The key attribute is represented by an ellipse with the text underlined.

Question 6

Describe composite

Answer 6

• An attribute that composed of many other attributes is known as a
composite attribute

Question 7

What is a multivalued attribute

Answer 7

• An attribute can have more than one value.

Question 8

W hat is derived entity

Answer 8

• An attribute that can be derived from other attribute is known as a derived
attribute.

Question 9

What is relationship

Answer 9

• A relationship is used to describe the relation between
entiti

Question 10

Mention types of keys

Answer 10

Primary key
Candidate key
Super key
Foreign key
Alternate key
Composite key
Artifici key

Question 11

Describe composite key

Answer 11

Whenever a primary key consists of more than one attribute, it is known as
a composite key.
• This key is also known as Concatenated Key.