1. CHAPTER 2. FUNDAMENTAL OF ENTITY RELATIONSHIP (ER)
Chapter 2- ERD

2. 2.1 Entity Relationship (ER) Model
2.1.1 Introduction
ER model is the constructs and conventions used to create a model of the user data.
The results are documented in an entity relationship diagram (ERD)
ERD is a diagram that depicts entity relationship model entities, attributes and relations. It also displays connectivity and cardinality.
Chapter 2- ERD

3. e.g : A Car Purchasing Model
FACTORY
PRODUCE
CUSTOMER
PURCHASED BY
ENTITY
RELATIONSHIP
The diagram above shows a car purchasing model that involves the relationship between the factory, car and customer. Here, we can see clearly that factory produces car and a customer purchases the car
Entity : FACTORY, CAR & CUSTOMER
Relationship : Produce & Purchased by.
Chapter 2- ERD

4. e. g: ER Model of Book Information System
PUBLISHER
publish
Written by
BOOK
AUTHOR
Books at E-Book bookstore are recorded. Information about publisher and the author will also be recorded to make sure that the process of searching for the book is easier
Chapter 2- ERD

5. Transformed to ERD PUBLISHER publish BOOK city Step 1 : 1 M
Publisher_Code
Publisher_Name
city
Book_Code
Title
Price
Type
Step 1 : 1 M
Relationship One to Many (1:M) : One publisher can publish many books while one book can only be published by one publisher
Chapter 2- ERD

6. Step 2 : M N BOOK publish AUTHOR
Book_Code
Author_No
Type
Price
Author_No M N
BOOK
publish
AUTHOR
Title
Author_Name
Publisher_Code
Book_Code
Relationship Many to Many (M:N) : One book can be written by many authors while one author can write many books
Chapter 2- ERD

7. Complete ERD M 1 BOOK PUBLISHER M N AUTHOR publish Written by Type
Publisher_Name
Book_Code
Price
Publisher_Code M 1
BOOK
PUBLISHER
publish M
city
Publisher_Code
Title
Written by
Book_Code
Author_No N
AUTHOR
Author_No
Author_Name
Chapter 2- ERD

8. 2.1.2 Elements of ER Model Element Symbol Definition Entity
There are 3 elements of ER Model :
Element
Symbol
Definition
Entity
A person, place, object, event or concept which you want to store information in database
Attribute
A property or characteristic of an entity or relationship type.
Relationship
Interaction of two entities represented by a verb.
Chapter 2- ERD

9. 2.1.3 Notation of ER Model Entity Relationship Simple Attribute
Multi valued
Composite Attribute
Derived Attribute
Chapter 2- ERD

10. 2.2 Entities And Attributes
2.2.1 Entity
Definition
Entity is a person, place, object, event or concept which you want to store the information in a database
Chapter 2- ERD

11. Continue….. Characteristics of entities :
Must have an attributes and unique key
Will become a table in a database
Classification of entities :
PERSON
Example : Student, Employee
PLACE
Example : Country, Branch
OBJECT
Example : Product, Building
EVENT
Example : Student Registration, Payment
CONCEPT
Example : Course, Order
Chapter 2- ERD

12. Continue…….. What is Entity Type ?
Entity type is a collection of entities, which share the same characteristics
What is Entity Instances ?
Entity instances are data for entity type
Chapter 2- ERD

13. Example Two entity instances for BOOK : P01 Access 2000 Processing
M-G1
Database
76.00
Yes
Entity Type : BOOK
Attribute : Book_Code
Book_title
Publisher_Code
Description
Type
Price
Book_cover
P02
Concepts of Database Management
P-H1
Database
100.00 No
Chapter 2- ERD

14. Attribute is a character of an entity or object.
Example :
Type
Price
Book_Code
BOOK
Title
Attributes for the entity BOOK are Book_code, Type, Price and Title
Chapter 2- ERD

15. 2.2.3 Types of Attributes Types of attributes Definition Example
Simple
An attribute that holds a single value
e.g: The majority of people have only one name
Multi valued
An attribute that have more than one value
e.g: A staff may have 2 tel_no.
Composite
An attribute that can be broken down into component parts
Derived
An attribute where the values can be calculated from related attribute
Name
Pnone-Num
State
Town
Postcode
Address
Date_of_birth
Age
Chapter 2- ERD

16. 2.3 Relationship and Cardinality Constraint
Definition : Relationship is an association
between entities, which is defined by a
diamond shaped symbol in an ERD
Chapter 2- ERD

17. Continue…. 2.3.2 Cardinality Constraint
Definition :The number of entity type, which
is involved in a relationship.
Types of cardinality constraint :
a). One to One Relationship (1:1)
Def : Maximum one X for each Y and one Y for each X
Manager_ID
Branch_ID 1 1
MANAGER
manage
BRANCH X Y
An employee (manager) can manage only one branch at one time and each branch only has one manager.
Chapter 2- ERD

18. Def : Maximum one X for each Y and possibly many Y’s for each X.
b). One to Many (1:M)
Def : Maximum one X for each Y and possibly many Y’s for each X.
Faculty_Name
Course_Code
Faculty_Name 1 M
offer
FACULTY
COURSE X Y
At university, one faculty offers many courses for students but one course is offered by one faculty only.
Chapter 2- ERD

19. Def : Possibly many X’s for each Y and many Y’s for each X
c). Many to Many (M:N)
Def : Possibly many X’s for each Y and many Y’s for each X
Author_ID
Author_ID
ISDN M N
Written by
BOOK
AUTHOR
ISDN
Composite entity
Author_ID & ISDN : Composite Key
A book may have more than one author and an author may write more than one book.
Chapter 2- ERD

20. 2.4 Relational Key and Integrity Constraint
2.4.1 Types of Key
Types of Key
Definition
Candidate key
An attribute or group of attributes that identifies a unique row in a relation. One of the candidate keys is chosen to be the primary key
Primary Key
Any of the candidates that are selected to be the key or an attribute that uniquely identifies each row in a relation.
Foreign Key
An attribute in a one table whose values must match the primary key in another table or whose value must be null.
Attribute that act as a primary key in a related table.
Composite Key
A primary key that consists of more than one attribute, especially in M:N relationship.
Chapter 2- ERD

21. Continue…. 2.4.2 Integrity Constraints 2 types of integrity constraint
a). Entity Integrity
Requirement : All entries are unique and no part
of a primary key may be null (no data).
Chapter 2- ERD

22. Continue…. b). Referential Integrity
Requirement : If foreign key exist in one table then the foreign key value must reference an existing primary key value in a table to which it is related and it can be null.
Chapter 2- ERD

23. Example : PUBLISHER BOOK
Publisher_Code
Name
City
F-B1
Fajar Bakti
Malaysia
M-G1
McGraw Hill UK
P-H1
Prentice Hall
T-H1
Thompson US
BOOK
Book_Code
Book_Title
Publisher_Code
Type
Price
P01
Access 2000 Processing
M-G1
Database
76.00
P02
Teach Yourself MS Access
80.00
P03
Concepts of Database Mgmt System
P-H1
100.00
P04
Pengajian Malaysia
T-H1
Pengetahuan am
40.00
P05
Graphic Design
F-B1
Graphic
88.00
Publisher_Code is a Primary Key for PUBLISHER table, but it is also a Foreign Key for BOOK table. Please note that Foreign Key value in table BOOK must match the Primary Key value in PUBLISHER table.
Chapter 2- ERD

24. Entity Relationship Diagram (ERD)
Definition :
ERD is a diagram that depicts entity relationship model entities, attributes and relations. It also displays connectivity and cardinality.
A tool used to represent graphically the association between entities in a system. View a system in term of entity and relationship.
Chapter 2- ERD

25. IDENTIFY RELATIONSHIP STATE CARDINALITY CONSTRAINTS
Steps to develop ERD
SKETCH ERD
IDENTIFY ENTITY
IDENTIFY RELATIONSHIP
STATE CARDINALITY CONSTRAINTS
SPECIFY PRIMARY KEYS
ADD ATTRIBUTES
Chapter 2- ERD

26. Exercise
Hospital Jaya is based in KL. This hospital has a few wards with several patients. This wards has a few types, which depends on type of patients.
Patient will be recorded into file that has ID Patient, Patient Name, Address, Phone Number, IC Number, Categories either VIP or regular patient and a group of blood patient
Each patient is treated by a doctor at one time but one doctor can treats a number of patients. The information of doctors recorded are : Doctor ID, name, address, phone number, IC number and specialization.
The nurses will be assigned to take care of the patients. Nurses in this hospital are graded based on their experience, qualification and duration of working in the hospital.
Draw a complete ERD based on the situation
Chapter 2- ERD