1. Database Design and Development
Entity Relationships

2. Learning Intention
I will learn about entity relationships.

3. Entity Relationships
We have already seen a number of relationships between different entities:
A vets customers and their pets
PS teachers and their pupils
Football players and their agents
Airline customers and their flights

4. One customer can have many pets.
Entity Relationships
An entity-relationship diagram is a graphical representation of the entities in a system. Shows the relationship between two or more entities.
e.g a vet surgeries customers and their pets:
One customer can have many pets.
Customer
Pet
is the owner of

5. Entity Relationships (cont)
entities
description of relationship
looks after contracts of
Agent
Player
one-to-many
(cardinality)
Each agent looks after many players.

6. Cardinality
A relationship between two entities can be one of the following:
one to one
e.g. one jockey rides one horse in a race
one to many
e.g. one coach teaches many players
many to many
e.g. many school pupils learn many subjects

7. Entity Relationships (cont)
Draw the entity relationship diagram for the relationship between the following entities. Include the entities, the description of the relationship and the cardinality.
Personal Support Teachers and Pupils
A Country and its Cities
TIME UP
5min min min min min

8. PS Support Teachers and Pupils
registers and teaches
PS Teacher
Pupil
One PS Teacher registers and teaches many pupils.

9. Countries and cities Country City
has within its borders
Country
City
One country has many cities within its borders.

10. Entity Relationship with attributes
Entity relationship diagrams can also be used to show the attributes of each entity:
Pet ID
Customer ID
Forename
Pet Name
is the owner of
Customer
Pet
Surname
Type of Animal
Customer ID*

11. Entity Relationship with attributes (cont)
Primary Keys are underlined.
Foreign Keys are marked with an asterisk *

12. Entity Relationships with attributes
Draw the entity relationship diagram including attributes for the following entities. Include the entities, the attributes, the description of the relationship and the cardinality.
Flights and Customers (see booklet)
Footballers and Agents (see booklet)
TIME UP
10min min min min min

13. Extension Task
Complete the Entity Relationships Extension Task sheet.

14. Success Criteria
I can describe and exemplify the entity-relationship diagram between two entities.