1-intro database systems

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Introduction toDatabase Systems


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Database and Database SystemA database is a shared collection of

logically related data designed to meet theinformation needs of an organization.

Components of a Database SystemsDatabase

Hardware

Software - DBMS

Users


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Database

The data in the database will beexpected to be both integrated and sharedparticularly on multi-user systems

Integration - The database may bethought of as a unification of severalotherwise distinct files, with anyredundancy among these files eliminated

Shared - individual pieces of data in thedatabase may be shared among severaldifferent users


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Hardware

These are secondary storage on which thedatabase physically resides, together with theassociated I/O devices, device controllers etc.


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DBMS

Examples of DBMS Products Oracle

Informix

Access

DB2

Fox pro

dBase SQL Server

My SQL


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Typical Function of DBMS

Data storage, retrieval and update

A user-accessible catalog

Transaction support

Concurrency and control services

Recovery services

Authorization services

Support of data communication

Integrity Services

Services to promote data independence

Utility services


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UsersApplication Programmer - writes

programs that use the database

Database Designers - designs

conceptual and logical databaseDatabase Administrator (DBA)Data Administrator

End - user - interacts with the systemfrom an on-line terminal by usingQuery Languages etc.


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Data & Database Administration

Data Administrator a business managerresponsible for controlling the overallcorporate data resources

Database Administrator (DBA) - a technicalperson responsible for development of thetotal system


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Sample Applications

Student Records Banking Insurance

Billing Systems e.g. Electricity, Phone ISPs Personnel Records

Accounting Systems Reservation Systems e.g. Airline, Hotel Medical Records


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Advantages

Control of dataredundancy

Data consistency

Multipurpose use of

data Sharing of data,

Enforcement ofstandards

Economy of scale Balance conflicting user

requirement

Improved dataaccessibility andresponsiveness

Increased productivity

Improved maintenancethrough dataindependence

Increased concurrency

Improved backup andrecovery services.


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Disadvantages

Complexity

Size

Cost of DBMS

Additional hardware costs

Cost of conversion


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Database Architecture

External Level concerned with the wayusers perceive the database

Conceptual Level concerned withabstract representation of the database inits entirety

Internal Level concerned with the waydata is actually stored


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Architecture of Db System

DBMS

Application 2Application 1 Application 3

Database

Conceptual

Level

Internal Level

External Level

Logical Data

Independence

Physical Data

Independence


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Data Independence

Logical Data Independence users and userprograms are independent of logical structureof the database

Physical Data Independence the separationof structural information about the data fromthe programs that manipulate and use thedata i.e. the immunity of application

programs to changes in the storage structureand access strategy


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Data Independence

Different applications will need different views ofthe same data, so that if they are not interested in a

part of the database, that part need not be included

in their view. This feature is also important forcontrolling access to parts of database

The DBA must have the freedom to change thestorage structure or access strategy in response to

changing requirements, without having to modifythe existing applications


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Db Development Life Cycle

Database planning System definition Requirement collection and analysis Database design DBMS selection Application design Prototyping Implementation Data conversion and loading Testing Operational maintenance


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Database Design

Conceptual database design - the process ofconstructing a model of the information usedin an organization, independent of all

physical considerations

Step 1 Build local conceptual data model foreach user view


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Database Design

Logical database design for the relationalmodel - the process of constructing a modelof the info used in an organization based on aspecific data model, but independent of aparticular DBMS and other physicalconsiderations

Step 2 Build and validate local data model foreach user view

Step 3 Build and validate global logical datamodel


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Database Design

Physical database design for relationaldatabases - the process of producing adescription of the implementation of the

database on secondary storage.

Step 4 Translate global data model for targetDBMS

Step 5 Design physical representation

Step 6 Design security mechanisms

Step 7 Monitor and tune the operational

system


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Conceptual Database Design

Step 1 Build local conceptual data model foreach user view

Identify entity types

Identify relationship types

Identify and associate attributes with entity orrelationship

Determine attributes domains

Determine candidate and primary key attributes

Specialize/generalize entity types (optional step)

Draw Entity-Relationship diagram

Review local conceptual data model with user


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Logical Database Design for theRelational ModelStep 2 Build and validate local data model for

each user view

Map local conceptual data model to local

logical data modelDerive relations from local logical data model

Validate model using normalization

Validate model against user transactions

Draw Entity-Relationship diagramDefine integrity constraints

Review local logical data model with user


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Logical Database Design for theRelational ModelStep 3 Build and validate global logical data

model

Merge local logical data models into global

modelValidate global data model

Check for future growth

Draw final Entity-Relationship diagramReview global logical data model with users


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Physical Database Design forRelational DatabasesStep 4 Translate global data model for target DBMS

Design base relations

Design enterprise constraints for target DBMS

Step 5 Design physical representation

Analyze transactions

Choose file organizations

Choose secondary indexes

Consider the introduction of controlled redundancy

Estimate disk space requirements


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Physical Database Design forRelational DatabasesStep 6 Design security mechanisms

Design user views

Design access rules

Step 7 Monitor and tune the operational system

1-intro database systems

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