Database Management Systems (DBMS)

Unit-2
Data Models
P Outline
Looping
• Basic concept of E-R diagram
• Types of Attributes
• Mapping Cardinality
• Weak Entity Sets
• Extended E-R features
• Generalization and Specialization
• Constraints on Specialization and Generalization
• Aggregation
• E-R diagram of Hospital Management System
• Reduction to E-R Database Schema
• Database Models
• Integrity Constraints
Section - 1
Basic concepts
} What is Database Design?
Ê Database Design is a collection of processes that facilitate the designing, development, implementation and
maintenance of enterprise database management systems.
} What is E-R diagram?
Ê E-R diagram: (Entity-Relationship diagram)
Ê It is graphical (pictorial) representation of database.
Ê It uses different types of symbols to represent different objects of database.

Prof. Venkatesh B 4
Entity
} An entity is a person, a place or an object.
Entity Name
} An entity is represented by a rectangle which contains the name of an entity.
} Entities of a college database are: Symbol
Ê Student
Ê Professor/Faculty
Ê Course
Ê Department
Student Faculty Course
Ê Result
Ê Class
Ê Subject

Exercise Write down the different entities of bank database.

Exercise Write down the different entities of hospital database.

Prof. Venkatesh B 5
Entity Set
} It is a set (group) of entities of same type.
} Examples:
Ê All persons having an account in a bank
Ê All the students studying in a college
Ê All the professors working in a college
Ê Set of all accounts in a bank

Prof. Venkatesh B 6
Attributes
} Attribute is properties or details about an entity. Attribute
} An attribute is represented by an oval containing name of an attribute. Name

} Attributes of Student are: Symbol

Ê Roll No
Ê Student Name Name
RollNo
Ê Branch
Ê Semester
Ê Address
Ê Mobile No Student
Ê Age
Ê SPI
Ê Backlogs

Exercise Write down the different attributes of Faculty entity.

Exercise Write down the different attributes of Account entity.

Prof. Venkatesh B 7
Relationship
} Relationship is an association (connection) between several entities.
} It should be placed between two entities and a line connecting it to an entity.
} A relationship is represented by a diamond containing relationship's name.

Relationship
Name

Symbol

Student Issue Book

Prof. Venkatesh B 8
E-R Diagram of a Library System

Primary Key Primary Key

Attributes
RollNo Name Relationship BookNo Name

Student Issue Book

Branch Sem Entities Author Price

Each and every entity must have one primary key attribute.
Relationship between 2 entities is called binary relationship.

Prof. Venkatesh B 9
Ternary Relationship
ProjectID Project Name

Project

FacID Name RollNo Name

Faculty Guide Student

Branch Technology Branch Sem

Relationship between 3 entities is called ternary relationship.

Prof. Venkatesh B 10
Exercise
} Draw an E-R diagram of following pair of entities
Ê Customer & Account
Ê Customer & Loan
Ê Doctor & Patient
Ê Student & Project
Ê Student & Teacher
§ Note: Take four attributes per entity with one primary key attribute.
Keep proper relationship between two entities.

Prof. Venkatesh B 11
Section - 2
Types of Attributes

Simple Attribute Composite Attribute

Cannot be divided into subparts Can be divided into subparts
E.g. RollNo, CPI E.g. Name
(first name, middle name, last name)
Address
(street, road, city)
Symbol Symbol Name

Roll No First name Last name

Middle name

Prof. Venkatesh B 13
Types of Attributes

Single-valued Attribute Multi-valued Attribute

Has single value Has multiple (more than one) value
E.g. RollNo, CPI E.g. PhoneNo
(person may have multiple phone nos)
EmailID
(person may have multiple emails)
Symbol Symbol

Roll No Phone No

Prof. Venkatesh B 14
Types of Attributes

Stored Attribute Derived Attribute

It’s value is derived or calculated from
It’s value is stored manually in database
other attributes
E.g. Birthdate E.g. Age
(can be calculated using current date and
birthdate)
Symbol Symbol
Birthdate Age

Prof. Venkatesh B 15
Entity with all types of Attributes

Middle
Name
First Name Last Name
Single
Simple
Value
RollNo Name Composite Apartment
Derived Composite

Age Student Address Street

Multiple Stored
Value
Phone No Birth Date Area

Prof. Venkatesh B 16
Exercise
} Draw an E-R diagram of Banking Management System.
} Draw an E-R diagram of Hospital Management System.
} Draw an E-R diagram of College Management System.
Ê Take only 2 entities
Ê Keep proper relationship between two entities
Ê Use all types of attributes

Prof. Venkatesh B 17
Descriptive Attribute
} Attributes of the relationship is called descriptive attribute.

Descriptive
Attribute

Issue
RollNo Name Date BookNo Name

Student Issue Book

Branch Sem Author Price

Prof. Venkatesh B 18
Role
} Roles are indicated by labeling the lines that connect diamonds (relationship) to rectangles
(entity).
} The labels “Coordinator” and “Head” are called roles; they specify Faculty entities interact with
whom via Reports_To relationship set.
} Role labels are optional, and are used to clarify semantics (meaning) of the relationship.

EmpID Name

Coordinator
Faculty Reports_To
Head

Branch Experience

Prof. Venkatesh B 19
Recursive Relationship Set
} The same entity participates in a relationship set more than once then it is called recursive
relationship set.
FacID FName DeptID DName

Faculty Works Department

Post Recursive
Relationship
FName Post Set DName
Ajay Professor Prof. Computer
f.
Haresh Professor PPrroof./ Civil
HO D
Ramesh HOD Mechanical

Prof. Venkatesh B 20
Section - 3
Mapping Cardinality (Cardinality Constraints)
} It represents the number of entities of another entity set which are connected to an entity
using a relationship set.
} It is most useful in describing binary relationship sets.
} For a binary relationship set the mapping cardinality must be one of the following types:
Ê One to One
Ê One to Many
Ê Many to One
Ê Many to Many

Prof. Venkatesh B 22
One-to-One relationship (1 – 1)
} An entity in A is associated with only one entity in B and an entity in B is associated with only
one entity in A.

customer borrow loan

A1 B1
C1 L1
A2 B2
C2 L2

C3 L3
A B

} Example: A customer is connected with only one loan using the relationship borrower and a
loan is connected with only one customer using borrower.

Prof. Venkatesh B 23
One-to-Many relationship (1 – N)
} An entity in A is associated with more than one entities in B and an entity in B is associated
with only one entity in A.

customer borrow loan

A1 B1
C1 L1
A2 B2
C2 L2

C3 L3
A B
L4

} Example: A loan is connected with only one customer using borrower and a customer is
connected with more than one loans using borrower.

Prof. Venkatesh B 24
Many-to-One relationship (N – 1)
} An entity in A is associated with only one entity in B and an entity in B is associated with more
than one entities in A.

customer borrow loan

A1 B1
C1 L1
A2 B2
C2 L2

C3 L3
A B
C4

} Example: A loan is connected with more than one customer using borrower and a customer is
connected with only one loan using borrower.

Prof. Venkatesh B 25
Many-to-Many relationship (N – N)
} An entity in A is associated with more than one entities in B and an entity in B is associated
with more than one entities in A.

customer borrow loan

A1 B1
C1 L1
A2 B2
C2 L2

C3 L3
A B
C4 L4

} Example: A customer is connected with more than one loan using borrower and a loan is
connected with more than one customer using borrower.

Prof. Venkatesh B 26
Mapping Cardinality (Cardinality Constraints) [Exercise]
} Draw an E-R diagram and specify which type of mapping cardinality will be there in the
following examples:
Ê Each customer has only one account in the bank and each account is held by only one customer. [single
account]
Ê Each customer has only one account in the bank but an account can be held by more than one customer.
[joint account]
Ê A customer may have more than one account in the bank but each account is held by only one customer.
[multiple accounts]
Ê A customer may have more than one account in the bank and each account is held by more than one
customer. [join account as well as multiple accounts]
Ê A student can work in more than one project and a project can be done by more than one student.
Ê A student can issue more than one book but a book is issued to only one student.
Ê A subject is taught by more than one faculty and a faculty can teach more than one subject.

Prof. Venkatesh B 27
Section - 4
Participation Constraints
} It specifies the participation of an entity set in a relationship set.
} There are two types participation constraints
Ê Total participation
Ê Partial participation

Partial participation Total participation

• some entities in the entity set may not participate in • every entity in the entity set participates in at least
any relationship in the relationship set. one relationship in the relationship set.
• indicated by single line • indicated by double line

customer borrow loan

C1 L1
Each customer has
maximum one loan C2 L2

C3
Prof. Venkatesh B 29
Section - 5
Weak Entity Set
} An entity set that does not have a primary key is called weak entity set.

Payment-date

loan-no amount payment-no Payment-amount

loan L_P payment

Strong Entity Weak Entity Weak Entity

Set Relationship Set

• Weak entity set is indicated by double rectangle.

• Weak entity relationship set is indicated by double diamond.

Prof. Venkatesh B 31
Weak Entity Set
} The existence of a weak entity set depends on the existence of a strong entity set.
} The discriminator (partial key) of a weak entity set is the set of attributes that distinguishes all
the entities of a weak entity set.
} The primary key of a weak entity set is created by combining the primary key of the strong
entity set on which the weak entity set is existence dependent and the weak entity set’s
discriminator.
} We underline the discriminator attribute of a weak entity set with a dashed line.
} Payment entity has payment-no which is discriminator.
} Loan entity has loan-no as primary key.
} So primary key for payment is (loan-no, payment-no).

Prof. Venkatesh B 32
Section - 6
Superclass v/s Subclass
Super Class Sub Class
A superclass is an entity from which another A subclass is an entity that is derived from
entities can be derived. another entity.
E.g, E.g,
an entity account has two subsets saving_account and current_account entities
saving_account and current_account are derived from entity account.
So an account is superclass. So saving_account and current_account are
subclass.

Account Super Class

Saving_Account Current_Account

Sub Class
Prof. Venkatesh B 34
Section - 7
Generalization v/s Specialization
Generalization Specialization
It extracts the common features of multiple It splits an entity to form multiple new entities
entities to form a new entity. that inherit some feature of the splitting entity.
Name Address Name Address

SPI Salary
Person Person
Name Name
ISA ISA
Address Address
Bottom-up approach

Student Faculty Student Faculty

SPI Salary SPI Salary

Prof. Venkatesh B 36
Generalization v/s Specialization
Generalization Specialization
The process of creation of group from various The process of creation of sub-groups within
entities is called generalization. an entity is called specialization.
It is Bottom-up approach. It is Top-down approach.
The process of taking the union of two or more The process of taking a sub set of higher level
lower level entity sets to produce a higher level entity set to form a lower level entity set.
entity set.
It starts from the number of entity sets and It starts from a single entity set and creates
creates high level entity set using some different low level entity sets using some
common features. different features.

Prof. Venkatesh B 37
Generalization & Specialization example

Name Address

PID City
Person

ISA

Salary Employee Customer Balance

ISA

Full Time Part Time

Days Worked Hour Worked

Prof. Venkatesh B 38
Exercise
} Give the examples of Generalization/Specialization in the following E-R diagram:
Ê Hospital Management System.
Ê College Management System.
Ê Bank Management System.
Ê Insurance Company.

Prof. Venkatesh B 39
Section - 8
Constraints on Specialization and Generalization

Constraints

Disjoint Participation

Non-disjoint Total Partial

Disjoint
(Overlapping) (Mandatory) (Optional)

Prof. Venkatesh B 41
Disjoint Constraint
} It describes relationship between members of the superclass and subclass and indicates
whether member of a superclass can be a member of one, or more than one subclass.
} Types of disjoint constraints
Ê Disjoint Constraint
Ê Non-disjoint (Overlapping) Constraint

Prof. Venkatesh B 42
Disjoint Constraint
} It specifies that the entity of a super class can belong to only one lower-level entity set (sub
class).
} Specified by ‘d’ or by writing disjoint near to the ISA triangle.
Employee
Cricketer (Super class)
(Super class)

Disjoint
Batsman Bowler ISA
(Sub class) (Sub class)

Full-time Part-time
(Sub class) (Sub class)

All the players are associated with only one sub class either (Batsman or Bowler).

Prof. Venkatesh B 43
Non-disjoint (Overlapping) Constraint
} It specifies that an entity of a super class can belong to more than one lower-level entity set
(sub class).
} Specified by ‘o’ or by writing overlapping near to the ISA triangle.
Employee
Cricketer (Super class)
(Super class)

Non-disjoint
Batsman Bowler ISA
(Sub class) (Sub class)

Faculty Head
(Sub class) (Sub class)

One player (Yuvraj singh) is associated with more than one sub class.

Prof. Venkatesh B 44
Constraints on Specialization and Generalization

Constraints

Disjoint Participation

Non-disjoint Total Partial

Disjoint
(Overlapping) (Mandatory) (Optional)

Prof. Venkatesh B 45
Participation (Completeness) Constraint
} It determines whether every member of super class must participate as a member of subclass
or not.
} Types of participation (Completeness) Constraint
Ê Total (Mandatory) participation
Ê Partial (Optional) participation

Prof. Venkatesh B 46
Total (Mandatory) Participation
} Total participation specifies that every entity in the superclass must be a member of some
subclass in the specialization.
} Specified by a double line in E-R diagram.
Employee
Cricketer (Super class)
(Super class)

Batsman Bowler ISA

(Sub class) (Sub class)

Professor Head
(Sub class) (Sub class)

All the players are associated with minimum one sub class either (Batsman or Bowler).

Prof. Venkatesh B 47
Partial (Optional) Participation
} Partial participation specifies that every entity in the super class does not belong to any of the
subclass of specialization.
} Specified by a single line in E-R diagram.
Employee
Cricketer (Super class)
(Super class)

Batsman Not associated with Bowler ISA

(Sub class) any sub class (Sub class)

Professor Head
(Sub class) (Sub class)

Prof. Venkatesh B 48
Section - 9
Limitation of E-R diagram
} In E-R model we cannot express relationships between two relationships.

Relation 1 Relation Relation 2

Entity 1 Relation Entity 2

Prof. Venkatesh B 50
Limitation of E-R diagram

Customer
Company

Employee Works Department

Customer
Can not connect two relationship

Borrow Borrow

Loan Loan

Process of creating an entity by combining various components of

E-R diagram is called aggregation.

Prof. Venkatesh B 51
Section - 10
E-R diagram of Hospital Management System

MRID
PatID Name HosID Name

Medical Record Has Patient Admitted Hospital

Report Name ISA T re a Has

ts

Indoor Outdoor
Doctor
RoomNo
IPDID OPDID DrID Dr Name
Charge

Prof. Venkatesh B 53
Section - 11
Reduce the E-R diagram to database schema

Step 1: Reduce Entities and Simple Attributes:

} An entity of an ER diagram is turned into a table. PersonID Name

} Each attribute (except multi-valued attribute) turns into

a column (attribute) in the table. Person
} Table name can be same as entity name.
} Key attribute of the entity is the primary key of the Address City
table which is usually underlined.
PhoneNo
} It is highly recommended that every table should start
with its primary key attribute conventionally named as
TablenameID.
Person (PersonID, Name, Address, City)

Prof. Venkatesh B 55
Reduce the E-R diagram to database schema

Step 2: Reduce Multi-valued Attributes: PersonID PhoneNo

} Multi-value attribute is turned into a new table.

Person
} Add the primary key column into multi-value
attribute’s table.
PhoneNo (PhoneID, PersonID, PhoneNo)
} Add the primary key column of the parent entity’s
table as a foreign key within the new (multi-value
Person (T1)
attribute’s) table. Foreign Key

} Then make a 1:N relationship between the Person

table and PhoneNo table. Having

PhoneNo (T2)

Prof. Venkatesh B 56
Reduce the E-R diagram to database schema
WifeID WName
Step 3: Reduce 1:1 Mapping Cardinality:

} Convert both entities in to table with proper attribute. Wife

} Place the primary key of any one table in to the

another table as a foreign key. Having

} Place the primary key of the Wife table WifeID in the

Person
table Persons as Foreign key.
OR
PersonID PName
} Place the primary key of the Person table PersonID in
the table Wife as Foreign key. Person (PersonID, PName)
Wife (WifeID, Wname, PersonID)

Wife (WifeID, Wname)

Person (PersonID, Pname, WifeID)

Prof. Venkatesh B 57
Reduce the E-R diagram to database schema
HouseID HName
Step 4: Reduce 1:N Mapping Cardinality:

} Convert both entities in to table with proper attribute. House

} Place the primary key of table having 1 mapping in to

the another table having many cardinality as a Foreign Having
key.
Person
} Place the primary key of the Person table PersonID in
the table House as Foreign key.
PersonID PName

Person (PersonID, PName)

House (HouseID, Hname, PersonID)

Prof. Venkatesh B 58
Reduce the E-R diagram to database schema
ActNo Balance
Step 5: Reduce N:N Mapping Cardinality:

} Convert both entities in to table with proper attribute. Account

} Create a separate table for relationship.

Has_Acct
} Place the primary key of both entities table into the
relationship’s table as foreign key.
Customer
} Place the primary key of the Customer table CID and
Account table Ano in the table Has_Acct as Foreign
CID CName
key.
Customer (CID, CName)
Account (ActNo, Balance)
Has_Acct (HasAcctID, CID, ActNo)

Prof. Venkatesh B 59
Summery of Symbols used in E-R diagram

Customer Name Hold

Entity Attribute Relationship

EmpID Age PhoneNo

Primary Key Derived Multi Valued
Attribute Attribute Attribute

Payment PymtID Issue

Weak Entity Discriminating Weak Entity

Attribute Relationship
Role
Name
E R E R ISA

Total Role Specialization/

Participation Indicator Generalization

Prof. Venkatesh B 60
Summery of Symbols used in E-R diagram

Disjoint
E R E ISA ISA
One to One Total Disjoint
Specialization/ Specialization/
E R E Generalization Generalization
One to Many

E R E Overlapping

Many to One ISA ISA

Partial Overlapping
E R E
Specialization/ Specialization/
Many to Many Generalization Generalization

Prof. Venkatesh B 61
Section - 12
What is a Database Models?
} A database model is a type of data model that defines the logical structure of a database.
} It determine how data can be stored, accessed and updated in a database management
system.
} The most popular example of a database model is the relational model, which uses a table-
based format.

Prof. Venkatesh B 63
Type of Database Models

Hierarchical Model

Network Model

Entity-relationship Model

Relational Model

Object-oriented database Model

Prof. Venkatesh B 64
Hierarchical Model
} The hierarchical model organizes data into a tree-like structure, where each record has a
single parent or root.
Department

Student Professor
} The hierarchy starts from the Root data, and expands like a tree, adding child nodes to the
parent nodes.
} In hierarchical model, data is organized into tree-like structure with one-to-many relationship
between two different types of data, for example, one department can have many professors
and many students.

Prof. Venkatesh B 65
Network Model
} This is an extension of the hierarchical model, allowing many-to-many relationships in a tree-
like structure that allows multiple parents.

B C

D E F

Prof. Venkatesh B 66
Entity-relationship Model
} In this database model, relationships are created by dividing object of interest into entity and
its characteristics into attributes.

Attributes
RollNo Name BookNo Name
Relationship

Student Issue Book

Branch Sem Entities Author Price

Prof. Venkatesh B 67
Relational Model
} In this model, data is organized in two-dimensional tables and the relationship is maintained
by storing a common attribute.

Rno Student_Name Age SubID Subject_Name Teacher

101 Raj Patel 20 1 DBMS Doshi
102 Meet Shah 21 2 DS Vyash
Foreign Key Foreign Key

ResID Rno SubID Marks

1 101 1 80
2 101 2 85
3 102 1 75
4 102 2 80

Prof. Venkatesh B 68
Object-oriented database Model
} This data model is another method of representing real world objects.
} It considers each object in the world as objects and isolates it from each other.
} It groups its related functionalities together and allows inheriting its functionality to other
related sub-groups.

Prof. Venkatesh B 69
Section - 13
Integrity Constraints
} Integrity constraints are a set of rules. It is used to maintain the quality of information.
} Integrity constraints ensure that the data insertion, updating, and other processes have to be
performed in such a way that data integrity is not affected.
} Thus, integrity constraint is used to guard against accidental damage to the database.
} Various Integrity Constraints are:
Ê Check
Ê Not null
Ê Unique
Ê Primary key
Ê Foreign key

Prof. Venkatesh B 71
Integrity Constraints
} Check
Ê This constraint defines a business rule on a column. All the rows in that column must satisfy this rule.
Ê Limits the data values of variables to a specific set, range, or list of values.
Ê The constraint can be applied for a single column or a group of columns.
Ê E.g. value of SPI should be between 0 to 10.
} Not null
Ê This constraint ensures all rows in the table contain a definite value for the column which is specified as not
null. Which means a null value is not allowed.
Ê E.g. name column should have some value.
} Unique
Ê This constraint ensures that a column or a group of columns in each row have a distinct (unique) value.
Ê A column(s) can have a null value but the values cannot be duplicated.
Ê E.g. enrollmentno column should have unique value.

Prof. Venkatesh B 72
Integrity Constraints
} Primary key
Ê This constraint defines a column or combination of columns which uniquely identifies each row in the table.
Ê Primary key = Unique key + Not null
Ê E.g. enrollmentno column should have unique value as well as can’t be null.
} Foreign key (referential integrity constraint)
Ê A referential integrity constraint (foreign key) is specified between two tables.
Ê In the referential integrity constraints, if a foreign key column in table 1 refers to the primary key column of
table 2, then every value of the foreign key column in table 1 must be null or be available in primary key
column of table 2.

Foreign Key

DeptID Dept_Name HOD RollNo Student_Name DeptID

1 Computer Doshi 101 Raj Patel 1
2 IT Vyash 102 Meet Shah 2

Prof. Venkatesh B 73
Questions asked in GTU
1. Write a note on mapping cardinality in E-R diagram.
2. Explain the difference between a weak and a strong entity set.
3. Explain the difference between generalization and specialization. OR Explain specialization
and generalization concept in E-R diagram with suitable example.
4. Write a note on constraints on specialization and generalization.
5. Explain aggregation in E-R diagram with example.
6. What do you mean by integrity constraints? Discuss various integrity constraints.

Prof. Venkatesh B 74
Questions asked in GTU [E-R diagrams]
7. Draw E-R diagram for Bank Management System.
8. Define E-R diagram. Draw an E-R diagram for Library Management System. Assume relevant
entities and attributes for the given system.
9. Construct an E-R diagram for a car-insurance company whose customers own one or more
cars each. Each car has associated with it zero to any number of recorded accidents.
10. Design a generalization–specialization hierarchy for a motor-vehicle sales company. The
company sells motorcycles, passenger cars, vans, and buses. Justify your placement of
attributes at each level of the hierarchy. Explain why they should not be placed at a higher or
lower level.

Prof. Venkatesh B 75
Questions asked in GTU [E-R diagrams and Database]
11. Design a database for an airline. The database must keep track of customers and their
reservations, flights and their status, seat assignments on individual flights, and the schedule
and routing of future flights. Your design should include an E-R diagram, a set of relational
schemas, and a list of constraints, including primary-key and foreign-key constraints.
12. Design a database for a hospital with a set of patients and a set of medical doctors.
Associate with each patient a log of the various tests and examinations conducted. Your
design should include an E-R diagram, a set of relational schemas, and a list of constraints,
including primary-key and foreign-key constraints.

Prof. Venkatesh B 76
 Database Management Systems (DBMS)
GTU # 3130703

Thank
You

Computer Engineering Department

Darshan Institute of Engineering & Technology, Rajkot
firoz.sherasiya@darshan.ac.in
9879879861