cs e 4 4 1: systems analysis & design
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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
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