Embed Size (px)
Citation preview
Chapter 2- ERD
CHAPTER 2. FUNDAMENTAL OF ENTITY RELATIONSHIP
(ER)
Chapter 2- ERD
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
e.g : A Car Purchasing Model
CARFACTORY
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
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
Transformed to ERD
Step 1 :
PUBLISHER publish BOOK
Publisher_CodePublisher_Name
city
Book_Code
Publisher_CodeTitle
Price
Type
Relationship One to Many (1:M) : One publisher can publish many books while one book can only be published by one publisher
1 M
Chapter 2- ERD
Step 2 :
BOOK publish AUTHOR
Price Type
Title Author_Name
Author_NoBook_Code
Publisher_Code
Author_No
Book_Code
M N
Relationship Many to Many (M:N) : One book can be written by many authors while one author can write many books
Chapter 2- ERD
Complete ERD
PUBLISHER
Publisher_CodePublisher_Name
city
1
Written by
BOOK
TitlePublisher_Code
Price
Type
Book_Code
publish
AUTHOR
M
Author_No Author_Name
Book_CodeAuthor_No
M
N
Chapter 2- ERD
2.1.2 Elements of ER Model
• 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
2.1.3 Notation of ER Model
Entity
Relationship
Simple Attribute
Multi valued
Composite Attribute
Derived Attribute
Chapter 2- ERD
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
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
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
Example
Entity Type : BOOK
Attribute : Book_Code
Book_title
Publisher_Code
Description
Type
Price
Book_cover
Two entity instances for BOOK :
P01
Access 2000 Processing
M-G1
Database
76.00
Yes
P02
Concepts of Database Management
P-H1
Database
100.00
No
Chapter 2- ERD
2.2.2 Attribute
• Attribute is a character of an entity or object.
Example :
BOOK
Book_Code
Title
Price
Type
Attributes for the entity BOOK are Book_code, Type, Price and Title
Chapter 2- ERD
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
Address
Town State Postcode
Age
Date_of_birth
Chapter 2- ERD
2.3 Relationship and Cardinality Constraint
2.3.1 Relationship
Definition : Relationship is an association
between entities, which is defined by a
diamond shaped symbol in an ERD
Chapter 2- ERD
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 manage BRANCH
Manager_IDBranch_ID
1 1
X Y
An employee (manager) can manage only one branch at one time and each branch only has one manager.
Chapter 2- ERD
b). One to Many (1:M)
Def : Maximum one X for each Y and possibly many Y’s for each X.
FACULTY offer COURSE
Faculty_Name Course_Code Faculty_Name
1 M
X Y
At university, one faculty offers many courses for students but one course is offered by one faculty only.
Chapter 2- ERD
c). Many to Many (M:N)
Def : Possibly many X’s for each Y and many Y’s for each X
BOOK Written by AUTHOR
ISDNAuthor_IDAuthor_ID
ISDNComposite entity
Author_ID & ISDN : Composite KeyA book may have more than one author
and an author may write more than one book.
M N
Chapter 2- ERD
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
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
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
Example :
Publisher_Code Name City
F-B1 Fajar Bakti Malaysia
M-G1 McGraw Hill UK
P-H1 Prentice Hall UK
T-H1 Thompson US
Book_Code Book_Title Publisher_Code Type Price
P01 Access 2000 Processing M-G1 Database 76.00
P02 Teach Yourself MS Access M-G1 Database 80.00
P03 Concepts of Database Mgmt System P-H1 Database 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.
PUBLISHER
BOOK
Chapter 2- ERD
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
Steps to develop ERD
IDENTIFY ENTITY IDENTIFY RELATIONSHIP SKETCH ERD
STATE CARDINALITY CONSTRAINTS
SPECIFY PRIMARY KEYS
ADD ATTRIBUTES
Chapter 2- ERD
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
