Higher Computing Science Entity Relationship Diagrams

2. Entity Relationship Diagrams
An entity-relationship diagram (ERD) is a graphical representation of a
database that shows the relationship between the entities in the database.

3. ERD Example 1
A company wants to build a database of their suppliers / parts. Below is an
example of one of the records they currently store:
Design an entity relationship diagram for the database.

4. ERD Example 1
Step 1 – State the entities:
Supplier
Sales Rep
Part

5. ERD Example 1
Step 2 – Link the entities
Sales RepSales Rep SupplierSupplier
employed by
PartPart
supplies

6. ERD Example 1
Step 3 – Complete the relationships
Sales RepSales Rep SupplierSupplier
employed by
PartPart
supplies

7. ERD Example 1
Step 4 – State any assumptions
Sales RepSales Rep SupplierSupplier
employed by
PartPart
supplies
Assumptions:
1.Only 1 sales rep per company
2.Only 1 supplier for each part

8. ERD Example 2
W Hansen & Partners are a collective of doctor's surgeries around the UK.
They want to design and build a database to help manage their business.
Below are some details:
1.W Hansen have 7 branches in total, and each branch employs between 3 and
14 GPs
2.GPs can only work at one surgery
3.Patients can only be registered at one surgery
4.Patients can have multiple appointments
5.For each appointment, the surgery stores the date, time, duration and any
notes
Produce an Entity Relationship Diagram for W Hansen & Partners

9. ERD Example 2
Step 1 – State the entities:
Branch
GP
Patient
Appointment

10. ERD Example 2
Step 3 – Link the entities
BranchBranch GPGP
employs
AppointmentAppointment
attends
PatientPatient
attends

11. ERD Example 2
Step 3 – Complete the relationships
BranchBranch GPGP
employs
AppointmentAppointment
attends
PatientPatient
attends

12. ERD Example 2
Step 4 – State any assumptions
BranchBranch GPGP
employs
AppointmentAppointment
attends
PatientPatient
attends
Assumptions:
1.There will only be one GP at any appointment
2.Only one patient can attend each appointment

13. Alternative ERD Layout
InsectInsect HabitatHabitatlives in
Insect Name
M 1
Latin Name Size
Habitat Name
Country Description
Type