1. CSE 441: Systems Analysis & Design
ERD - DATA MODELLING
LAB 3
Yusuf Altunel

2. What is an Entity Relationship
Diagram (ERD) ?
Identify the entities required by the business
An entity corresponds to a
Person
Place
Event
Concept
Entities have relationships
“friends” may have many “addresses”
Relationships are evaluated in both directions
“One friend may have many telephones”
or “One telephone belongs to a single friend”

3. Four Basic components of E-R Diagrams
1. entity: a "thing" in the real world
a Book, a publisher, a customer
2. attribute: a property of an entity a Book’s Title, a customer’s name
3. key: usually one attribute identifies an entity
the ISBN for a book, Account number
4. relationship: a link between two entities
a book and its publisher:
publishes, published by
customer who placed an order for item(s)
orders, ordered by

4. Entities: Examples In a Hospital Administration System Patient Doctor
Operation
Medicine
...

5. Look at the following list and decide which you think are likely candidates for entities
A member of staff in a personal system.
A book in a library system
A customer’s address in a sales system
A customer in a sales system
A National Insurance number in a payroll system
A patient in a medical records system
The library in a library system * * * *

6. Some Data Items for each of these entities can be:
1. Name, address, date of birth
2. Book title, author, publisher
4. Name, address, credit limit
6. National Insurance number, date of birth

7. Attributes A special and very important type of attribute
A key attribute:
A special and very important type of attribute
uniquely identifies a specific entity.

8. Choose likely key and non-key attributes for the following entities:
1. A car in a vehicle registration system
Car’s registration number, type, model, date of manufacture
2. An employee in a payroll system
Employee number or Payroll number, Name, address, department, tax code, etc.
3. A stock item in a stock control system
Stock number, Description, amount in stock, price, etc. * * *

9. Reading an Entity-Relationship Diagram

10. Tips on Building ERD Nouns are clues to the entities of a business
Start by describing the work that is done in the project, then pull out nouns in the sentences for entities.
- My address book contains adresses and telephone numbers for both friends and businesses
Verbs and adjectives sometimes help to get relationships between entities.
- Friends have adresses