Chapter 2

Question 1

What’s the purpose of creating an ER diagram?

Answer 1

• To design the conceptual model of the database.

Question 2

What is an entity in the ER diagram?

Answer 2

• Real world object distinguishable from other objects. An entity is described using a set of attributes

Question 3

What’s an entity set?

Answer 3

• A collection of similar entities. ie. All employees

- All entities in the entity set have the same attributes

Question 4

What is the purpose of a relationship?

Answer 4

• It provides an association between two or more entities

Question 5

What are the 4 types of relationships?

Answer 5

• One to one
• One to many
• Many to one
• Many to many

Question 6

What is a weak entity?

Answer 6

• It can only be identified by considering the primary key of another owner entity
• Owner entity set and weak entity set must participate in a one to many relationship set
• Weak entity must have total participation in this identifying relationship set.

Question 7

Describe how the ISA hierarchy works and what is its purpose?

Answer 7

• Similar to inheritance in object oriented languages. Attributes of parent are inherited.