Remember

By ILTAF MEHDI (MCS, MCSE, CCNA)

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Distribution of MarksFor

Second SemesterInternal Sessional Evaluation External

Evaluation

Assignment/Project

Quizzes

Class Attendan

ce

Mid-Term Test

Total Session

al

Terminal Exam

Final Evaluati

on

10 10 5 25 50 50 100

Remember


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Chapter No

Chapter NamePage No

1. Database Foundation OR An Overview of Database Management System (DBMS)

2. Semantic Modeling OR Entity Relationship Model (ERD)

3. An introduction to Relational Database

4. Normalization

5. Relational Algebra

6. An Introduction to Structured Query Language (SQL)

Course Contents


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COURSE TITLE:

DATABASE-1

COURSE INSTRUCTOR:ILTAF MEHDI

Ch

ap

ter

No:

02

Ch

ap

ter

No:

02


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ENTITY RELATIONAL (E-R) MODEL

E-R Model: “An entity Relationship Model is a

logical representation of data for an organization or for a business area”.

The E-R Model is expressed in terms of entities in the business environment, the relationships or associations among entities and the attributes of both the entities and relationships.


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ENTITY RELATIONSHIP DIAGRAM

E-R Diagram: An E-R model normally expressed as an

entity relationship diagram. Where “the E-R Diagram is a graphical representation of an entity relationship model”.


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E-R MODEL NOTATIONS

There is no industry standard notation for the E-R model. But some basic notations combine most of the desirable features of the different notations that are commonly used.

The basic notations used for E-R model are given on the next slide.


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E-R MODEL NOTATIONS

Associative Entity

Attribute

Multi-Valued Attribute

Derived Attribute

Strong Entity

Weak Entity

Relationship

Identifying Relationship


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E-R MODEL CONSTRUCTS

The basic constructs of the E-R model are:

1) Entities2) Attributes3) Relationships or Associations


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1. Entity: “An entity is a person, place, object, event or concept

in the user environment about which the organization whishes to maintain data”.

Some examples of each of these types of entities are given below:

PERSON: Employee, Student, Patient etcPLACE: City, State, Country etcOBJECT: Machine, Building, Automobile etcEVENT: Sale, Registration, Renewal etcCONCEPT: Account, Course, Work Center etc


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TYPES OF ENTITY

Following are the major types of the entity:

a) Entity Typeb) Entity Instancec) Strong Entity Typed) Weak Entity Type


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TYPES OF ENTITY1. Entity Type: “A collection of entities that share common properties

or characteristics is called entity type”. Entity type is also called Entity Class.2. Entity Instance: “The single occurrence of an entity type is called

entity instance”. An entity Type is described just once in a database,

while many instances of that entity type may be represented by data stored in the database.

For example: An entity Type “Employee” has many entity instances

in organization.


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TYPES OF ENTITY

3. Strong Entity Type: “An entity that exists independently of

other entity types is called Strong Entity Type”.

4. Weak Entity Type: “An entity Type whose existence

depends on some other entity type is called Weak Entity Type”.


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TYPES OF ENTITY

5. Identifying Relationship: “The relationship between weak entity

type and its owner is called Identifying Relationship”.

6. Identifying Owner: “The entity type on which the weak

entity type depends is called Identifying Owner”.


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DEPENDENT

EMPLOYEE Has

Emp-Id Emp-Name

Dependent-Name Date-Of-

Birth

STRONG ENTITYOR

IDENTIFYING OWNER

IDENTIFYING RELATIONSH

P

WEAK ENTITY

Attributes


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2. Attribute: “A property or characteristics of an entity

type that is of an interest to the organization is called attribute”.

Following are some entity types and their attributes, (shown by shorthand notation):

STUDENT (st-Id, st-Name, st-F/Name, st-Address etc) EMPLOYEE (Emp-id, Emp-Name, Emp-Skill etc) AUTOMOBILE (Vechile-id, Vechile-Color, Vechile-Weight

etc )


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TYPES OF ATTRIBUTES

Following are the major types of attribute:

1) Simple Attribute2) Composite Attribute3) Multi-Valued Attribute4) Derived Attribute5) Identifier6) Composite Identifier


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TYPES OF ATTRIBUTES1. Simple Attribute: “An attribute that can’t be broken down into

smaller components is called Simple Attribute”.For example: All Attributes associated with AUTOMOBILE are Simple

Attributes.2. Composite Attribute: “An attribute that can be broken down into

components is called Composite Attribute”.For example: “Address” attribute is a Composite Attribute which

can be broken down into Street-Add, City-Add, State-Add and Postal-Code.


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TYPES OF ATTRIBUTES3. Multi-Valued Attribute: “An attribute that may take on more than one

value for a given entity instance is known as Multi-Valued Attribute”.

Multi-Valued Attribute is indicated by “double ellipse” in an E-R Diagram.

4. Derived Attribute: “An Attribute whose values can be calculated

from related attribute value is known as Derived Attribute”.

Derived Attribute is indicated by “ellipse with dashed line” in an E-R Diagram.


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EMPLOYEE

Emp-Id Emp-Name

Emp-Address

SkillYear-Employed

Composite Attribute

Multi-Valued Attribute

Derived Attribute

Identifier

Date-Employed


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TYPES OF ATTRIBUTES

5. Identifier: “An Attribute that uniquely identifies individual

instances of an entity type is called Identifier or Key”.

Identifier name or key is underlined in E-R diagram.6. Composite Identifier: “An identifier that consists of a composite attribute

is known as Composite Identifier or key”. Composite Identifier or key is underlined while the

components are not underlined in E-R diagram.

SEE THE EXAMPLES ON NEXT SLIDE


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STUDENT

st-Id st-Name Other attributes

In the above E-R diagram, the Identifier for STUDENT entity type is “st-Id” (Student-ID).

FLIGHT

Flight-Id

No-of-passengers

In the above E-R diagram, the composite Identifier for FLIGHT entity type is “Flight-Id” .

DateFlight-No


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E-R MODEL CONSTRUCTS3. Relationship: Relationship is also called association. Def:“An association is a logical relation between data items”.

OR “the meaningful connection between data items is called

relationship or association ”.OR

“An association is a relationship between the instances of one or more entity types that is of an interest to the organization”.

Diamond symbol is used to show the relationship between entities.

For example:

student

has Reg-No

Relationship


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DEGREE OF ASSOCIATION OR RELATIONSHIP

Def: “The number of entity types that participate in a relationship is known as Degree of association or relationship”.

Associations may be:i. Unary (Degree 1)ii. Binary (Degree 2)iii. Ternary (Degree 3)


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RELATIONSHIP DEGREE

a. Unary Relationship

b. Binary Relationship

c. Ternary Relationship


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TYPES OF ASSOCIATION AND REVERSE ASSOCIATION

There are three main types of association and reverse association. Which are given below:

1) One to One Relationship2) One to Many Relationship (or

Many to One)3) Many to Many Relationship


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TYPES OF RELATIONSHIP

1. One to One Relationship: “When one occurrence of entity A can relate to one and only

one occurrence of entity B and reversely the occurrence of entity B can relate to one and only one occurrence of entity A is called one to one relationship”.

One to One Relationship can be represented by one-head arrow.

For example: “Student has only one Reg-no” and reversely “On one Reg-no there must be only one Student”.

Similarly,“A Patient can have only one Bed” and reversely “On one Bed there must be only one Patient”

Student Reg-no

Patient BedA B

A B


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2. One to Many Relationship (or Many to One): “When One occurrence of entity A can relate to

many occurrences of entity B then it is called One to many relationship but reversely when an occurrence of entity B can relate to only occurrence of entity A then it is called Many to one relationship”.

One to Many Relationship can represented by double-head arrow.

For Example: “A Mother can have many Childs” but reversely “a Child can have only one Mother”.

Mother ChildA B


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3. Many to Many Relationship: “An occurrence of entity A can relate to more

occurrences of entity B and reversely an occurrence of entity B can relate to more occurrences of entity A is called Many to Many Relationship”.

For example: “A Student can have many teachers” and reversely “A Teacher can have many students”.

Similarly, “A Student can take many courses” and reversely “A Course can be taken by many students”.

Student CourseA B

Student TeacherA B


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RELATIONSHIP CARDINALITY

Mandatory One

Mandatory Many

Optional Many

Optional One

Remember

Documents

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