Database Design by Kamalakar Dandu

8/2/2019 Database Design by Kamalakar Dandu

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Database Design

Requirement Formulation and AnalysisCollection and documentation of requirement

Analysis of Requirement Conceptual Design

Data ModelingFirst Level E-R Modeling

Second Level NormalizationE-R ModelingPhysical Design and Implementation


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Database design is the process of developing

database structures to hold data to cater to user

requirements. The final design must satisfy user

needs in terms of completeness integrity,

performance and other factors.

For a large enterprise, the database design willturn out to be an extremely complex task leaving a

lot to the skill and experience of the designer.

A number of tools and techniques, including

computer-assisted techniques, are available tofacilitate database design.


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Requirement Formulation and Analysis

The primary input to the database design processis the organizations statement of requirements.poor definition of these requirements is a major

cause of poor database design, resulting indatabases of limited scope and utilities which areunable to adapt change.

Requirement analysis is the process of identifying

and documenting the data the user requires in thedatabase to meet present and future informationneeds. During this phase, the analyst studies dataflows and decision making processes in theorganization and works with the users.


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The objective of this phase is to answer the

following question:

What are user-views of the data(present and

future)?

What data elements(or attribute) are required in

these user-views?

What are the entities and their primary keys?

What are the operational requirements regardingsecurity, integrity and response time?


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Conceptual Design

The major step in conceptual design is to

identify the entities and relationships that

reflect the organizations data, naturally.The objective of this step is to specify the

conceptual structure of the data and is often

referred to as data modeling. The E-Rmodel, with an emphasis on the top-down

approach.


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Data Modeling

Describes relationship between data objects

First LevelEntity relationship diagrams

Second LevelNormalization

The relationship between the collection of data in a system maybe graphically represented using data modeling. If therelationship are complex, data modeling provides a simplifiedapproach to the structured design of the system. It helpsdetermine the data objects in the system, the composition of

each, and the relationship that exist between them.

Data modeling is achieved in two levelsthe first level buildsthe conceptual model of the data, using E-R Modeling. Thesecond level organized this model better, by removing

redundancies, through a process called Normalization. Thenormalized model is then converted into the physical database.


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Entity Relationship Diagram

Entity Relationship Modeling is a technique

for analysis and logical modeling of a

systems data requirements. It uses threeconcepts, entities, their attributes and the

relationships that exist between the entities.

It uses graphical notations for representingthese.


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Graphical Notations for E-R diagram

Name : Entity

Symbol :

Function :data objects in the system

uniquely identifiable by identifier has

attributes that describe it.


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Name: Attributes

Symbol:

Function: Describe an entity.

Name: Relationship

Symbol:

Function: Relates two entities uniquely

identified by the identifier.


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Normalization

Normalization is the process of refining the data modelbuilt by the Entity-Relationship diagram. TheNormalization technique, logically groups the data over anumber of tables, with minimum redundancy of data. The

entities of tables resulting from Normalization contain dataitems, with relationships being represented by replicationof key data item(s).

The first step towards Normalization is to convert the E-Rmodel into Tables of relations. The next step is to examine

the tables for redundancy and if necessary, change them tonon-redundant forms. This non-redundant model is thenconverted to a database definition, which achieves the

objective of the Database Design Phase.


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Need for Normalization

Improves database design

Ensures minimum redundancy of data.

Reduces need to reorganize data when

design is modified/enhanced.

Removes anomalies for database activities.


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Steps in Normalization

First Normal Form (1 NF)

Second Normal Form (2 NF)

Third Normal Form (3 NF)


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First Normal Form (1 NF)

Identify repeating groups of fields

Remove repeating groups to a separate table

Identify the keys for the tables.

Key of parent table is bought as part of the

concatenated key of the second table.


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Second Normal Form (2 NF)

Check if all fields are dependent on thewhole key.

Remove fields that depends on part of thekey.

Group partially-dependent fields as a

separate table Name the tables

Identify key(s) to the table(s)


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Third Normal Form (3 NF)

Remove fields that

depend on other non-key attribute

can be calculated or derived from logic

Group interdependent fields as separate

tables, identify the key and name the table.

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Database Design by Kamalakar Dandu