Punjab College Of Technical Education

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E-R Model E-R Model: Entities.

Attributes.

Relationship.

Steps to form E-R Model: Identify Entities.

Find Relationship.

Draw rough E-R.

Fill the cardinality.

Define Primary key.

Draw key based ERD.

Identity Attributes.

Map Attributes.

Draw full attribute of ERD.

Check Result.

OBJECTIVES• Store Information in Systematic Manner

• Reduce the Problem of End-user

• Easy to Store an Retrieval

• Track the Information

Users

• Different users can access data• Depending on their degree of expertise users

are classified in the following groups– Naïve Users (ATM user)

– Online Users– Application Programmers– Sophisticated Users– DBA

Entity Relationship Model

• Entity – It is anything real or abstract about which we

want to store the data .

• Relationship – It specifies the association that

exists between one or more entities.

• Attribute – It is the characteristic which is common to

all or most instances of particular entity.

Dependencies

What is Dependencies?

Types of Dependencies

Partial key Dependencies.

Primary key Dependencies.

Transitive key Dependencies.

Functional key Dependencies.

Generalization

Student

Grad Student Post Grad Student

Specialization

Normalization

• It is a process during which redundant relation schemas are

decomposed by breaking up their attributes in to smaller

relation schemas that possess desirable properties.

1. First N/F

2. Second N/F

3. Third N/F

4. BNC N/F

Eliminate Repeating Groups

Second N/FFirst N/F

Third N/FBC N/F

Removing Partial key dependency

Eliminate Transitive key dependency

Eliminate Functional dependency

Normalization Form

Attributes

• Characteristics of entities

• Domain is set of possible values

• Primary keys underlined

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Relationships• Association between entities• Connected entities are called participants• Operate in both directions• Connectivity describes relationship classification– 1:1, 1:M, M:N

• Cardinality– Expresses number of entity occurrences associated

with one occurrence of related entity

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Comparison of E-R Modeling Symbols

Figure 3.36

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15

Employee Table

16

Student Table

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Completed ERD

Keys

• Candidate Key– A minimal set of attributes that uniquely identifies a tuple

• Primary Key– The candidate key chosen as the identifying key of the

relation

• Alternate Key– Candidate keys which are not primary keys

• Foreign Key– An attribute (or set of attributes) in table R1 which

also occurs as the primary key of relation R2. – R2 is called the referenced relation. – Foreign keys are also called connection keys or

reference attributes.

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Database vs. File SystemsFigure 1.6

DFD Zero LevelStudent Teacher

WebSite

Course Database Department

Level 1Student Teacher

Student result assignment Teacher T.T Teacher table

Student Table Teacher Table

WEBSITE DATABASE

Course Table Department Table Course Department Table

ER Of Student

Department + Course

Class With Professors(Plus Project Or Assignment)

ER Relationship

Contd…

BY HASH Generation

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