CSE 441: Systems Analysis & Design

ERD - DATA MODELLINGLAB 3Yusuf Altunel

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”

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

Entities: Examples

In a Hospital Administration SystemPatient Doctor Operation Medicine...

Look at the following list and decide which you think are likely candidates for entities

1. A member of staff in a personal system.2. A book in a library system 3. A customer’s address in a sales system4. A customer in a sales system5. A National Insurance number in a

payroll system6. A patient in a medical records system7. The library in a library system

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1. Name, address, date of birth2. Book title, author, publisher4. Name, address, credit limit6. National Insurance number,

date of birth

Some Data Items for each of these entities can be:

Attributes

A key attribute:A special and very important

type of attribute uniquely identifies a specific entity.

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.

Choose likely key and non-key attributes for the following entities:

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Reading an Entity-Relationship Diagram

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