Upload
yetta-leon
View
15
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Remember. Course Contents. Chapter No: 02. Chapter No: 02. COURSE INSTRUCTOR : ILTAF MEHDI. Course Title : Database-1. E-R Model: “An entity Relationship Model is a logical representation of data for an organization or for a business area”. - PowerPoint PPT Presentation
Citation preview
By ILTAF MEHDI (MCS, MCSE, CCNA)
1
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
By ILTAF MEHDI (MCS, MCSE, CCNA)
2
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
By ILTAF MEHDI (MCS, MCSE, CCNA)
3
COURSE TITLE:
DATABASE-1
COURSE INSTRUCTOR:ILTAF MEHDI
Ch
ap
ter
No:
02
Ch
ap
ter
No:
02
By ILTAF MEHDI (MCS, MCSE, CCNA)
4
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.
By ILTAF MEHDI (MCS, MCSE, CCNA)
5
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”.
By ILTAF MEHDI (MCS, MCSE, CCNA)
6
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.
By ILTAF MEHDI (MCS, MCSE, CCNA)
7
E-R MODEL NOTATIONS
Associative Entity
Attribute
Multi-Valued Attribute
Derived Attribute
Strong Entity
Weak Entity
Relationship
Identifying Relationship
By ILTAF MEHDI (MCS, MCSE, CCNA)
8
E-R MODEL CONSTRUCTS
The basic constructs of the E-R model are:
1) Entities2) Attributes3) Relationships or Associations
By ILTAF MEHDI (MCS, MCSE, CCNA)
9
E-R MODEL CONSTRUCTS
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
By ILTAF MEHDI (MCS, MCSE, CCNA)
10
TYPES OF ENTITY
Following are the major types of the entity:
a) Entity Typeb) Entity Instancec) Strong Entity Typed) Weak Entity Type
By ILTAF MEHDI (MCS, MCSE, CCNA)
11
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.
By ILTAF MEHDI (MCS, MCSE, CCNA)
12
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”.
By ILTAF MEHDI (MCS, MCSE, CCNA)
13
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”.
By ILTAF MEHDI (MCS, MCSE, CCNA)
14
DEPENDENT
EMPLOYEE Has
Emp-Id Emp-Name
Dependent-Name Date-Of-
Birth
STRONG ENTITYOR
IDENTIFYING OWNER
IDENTIFYING RELATIONSH
P
WEAK ENTITY
Attributes
By ILTAF MEHDI (MCS, MCSE, CCNA)
15
E-R MODEL CONSTRUCTS
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 )
By ILTAF MEHDI (MCS, MCSE, CCNA)
16
TYPES OF ATTRIBUTES
Following are the major types of attribute:
1) Simple Attribute2) Composite Attribute3) Multi-Valued Attribute4) Derived Attribute5) Identifier6) Composite Identifier
By ILTAF MEHDI (MCS, MCSE, CCNA)
17
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.
By ILTAF MEHDI (MCS, MCSE, CCNA)
18
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.
By ILTAF MEHDI (MCS, MCSE, CCNA)
19
EMPLOYEE
Emp-Id Emp-Name
Emp-Address
SkillYear-Employed
Composite Attribute
Multi-Valued Attribute
Derived Attribute
Identifier
Date-Employed
By ILTAF MEHDI (MCS, MCSE, CCNA)
20
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
By ILTAF MEHDI (MCS, MCSE, CCNA)
21
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
By ILTAF MEHDI (MCS, MCSE, CCNA)
22
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
By ILTAF MEHDI (MCS, MCSE, CCNA)
23
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)
By ILTAF MEHDI (MCS, MCSE, CCNA)
24
RELATIONSHIP DEGREE
a. Unary Relationship
b. Binary Relationship
c. Ternary Relationship
By ILTAF MEHDI (MCS, MCSE, CCNA)
25
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
By ILTAF MEHDI (MCS, MCSE, CCNA)
26
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
By ILTAF MEHDI (MCS, MCSE, CCNA)
27
TYPES OF RELATIONSHIP
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
By ILTAF MEHDI (MCS, MCSE, CCNA)
28
TYPES OF RELATIONSHIP
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