Databases Ys

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Module-II

Database and databasemanagement system


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Difference between files and Relationaldatabase

Files1. Store data in one

dimensional files

2. Stores, organize

and retrieveinformation fromone file at a time

3. Leave the

management ofdata relationshipsto the applicationsthat access the

data.

Relational database1. Store data in twodimensionaltables

2. Store organizesand retrieveinformation islinked by acommon columnor field

3. Establishrelationshipsbetween files andviews within the

database itself.


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4. Require aprogrammer towrite code for datamanagementfunctions.

5. Files are createdand maintained byapplicationprograms.

6. Are often

associated witholder programs onmainframe andmid-range system.

4.Are typically createdand maintained by

databaseadministrators.

5.Are popular on

UNIX processorsand powerful serverwithin aclient/server

framework6. Consists a database

engine thatperforms differentfunctions.


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Database

Database is an integrated and well defined

data and information,centrally controlled in allits aspects,created and stored in atypicalstructure for an organization.

In an organization the database could be one

or more depending upon the needs and theoperations of the organization.

The data structure and its storage should besuch that it facilitates

sharability,availability,and integrity of data.Database excludes transient data such asreports,input documents,intermediate resultsobtained during processing


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Objectives of Database

1. Controlled Redundancy

2. Ease of learning and use

3. Data independence4. More information at low cost

5. Accuracy and integrity

6. Recovery from failure7. Privacy and security

8. Performance


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Advantages of Database Approach

All the three levels of management use thesame database hence any report using the

information will be consistentAll the three levels of management view thedatabase as per their needs.

The application systems can be developedindependent of the database.The data validation and updating will be onceand same for all

The data is shared by all userData security and privacy can be managed

AS the database is a storage of structuredinformation the queries can be answered fast.


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User programs

Application program or queries

Software to process

Queries/Programs

S/W to access

Stored Data

Stores

database

definition

Stored data

base


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Major types of databases used byOrganization and users

Computer using organizations havefive types of databases.

1. Common operational database

2. Common end user database

3. Distributed database

4. Personal and end user databases and5. External database


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databases

These databases consists of avariety of data files developed byend users at their

workstations.Users may have theirown electronic copies ofdocuments they generated withword processing packages orreceived by e-mails, fromelectronic spreadsheets and DBMSpackages.


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Distributed databaseThese are databases of local work groupsand departments at regional office,branchoffices manufacturing plant and other worksites.These database can include segments

of both common operational and commonuser databases as well as data generatedand used only at a users own site.


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Common operational databaseThese databases store detaileddata needed to support theoperation of entire

organization.They also calledsubject areadatabases,transaction databases

and production databases.For example Customerdatabase,personnel

database,accounting database


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These databases store data and

information extracted from selectedoperational and external databases.theyconsists of summarized data andinformation most needed by theorganisation managers and other endusers.They are also called informationdatabases and management databases

and accessed by executive and users aspart of DSS And EIS to supportmanagerial decision making.


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External databases

These can be accessed from large,privatelyowned databases or databanks available fora fee to end users and organisations fromcommercial information service

networks.Data is available in the form ofstatistics on economic and demographicactivity from statistical data banks; abstracts

from hundreds of newspapers,magazines andother periodicals from bibliographic databanks.


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Data base management system

DBMS is a collection of programs that enables users to create and maintain

a database.The DBMS is a general purpose software system that facilitatesthe processes of defining,constructing and manipulating databases forvarious applications.

Defining database involves specifying the data type structures andconstraints for the data to be stored in the database.

Constructing the database is the processes of storing the database itselfon the storage medium that is controlled by DBMS.

Manipulating includes the updating of database or editing the databaseand generating reports from the data.

The DBMS is a S/W or a set of rules and methods that allows for

defining,creating,updating,reading ,maintenance and protection ofthe database.


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DBMS consists of a collection of inter-related

data and a set of programs to access thatdata.The collection data is usually referred toas database which contains information aboutone particular enterprise.

The primary goal of a DBMS is to provide anenvironment that is both convenient andefficient to use retrieving and storing database

information.DBMS is the interface between the user ofapplication programs on one hand and the

database on other.


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DBMS

DBMS as interface between applicationprogram and data base

User(or)

Application

program

DBMS Data base


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Major users of a DBMSpackage

Database integration and reporting

Application development

Database access and maintenance

Database creation and modification


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Components to a DBMS

These are:-

1. At least one person who owns' and isresponsible for the database.

2. A set of rules and relationships that defines

and governs the interactions amongelements of the database.

3. People who put data into the database

4. People who get data out of the database5. The database itself.


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Components of DBMS

DDL

DML

SQL

f


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Functions of DBMS

1. Organizes data:-Data are organised according to thespecifications of DDL.These are specified by the DBA at thetime of creation of database.

2. Integrates data:- Data are interrelated or linked together atthe elements level and can,therefore be assembled in manycombinations during execution of a particular applicationprogram.

3. Separates data:-A DBMS servers as a filter betweenapplication program and their associated data.It separatesthe logical description and relationship of data from the wayin which the data are physically stored.

4. Controls data: A DBMS appears to an applicationprogrammer to be an extension of the O.S S/W .As it receivesdata requests from host programs,it controls how and where

data are physically stored.5. Retrieves data:A record of data can be obtained via

DBMS1.Serially 2.Sequentially 3.Randomly by address4.Randomly by key 5. By structural link

6. Protects :A DBMS protects and secures both the content ofa database and relationships of data element . Data areprotected against by unauthorized users,physical damage,OS


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Data dictionary1. It is an encyclopedia of information concerning each

data element.It describes the data and its

characteristics,such as location,size,type of data,itidentifies the origin,the use,the ownership,and themethod of accessing and securing data.

2. The data dictionary can exist either on paper or as a

computer file.When it exist as a file,special S/W isnecessary to create and maintain it,and make itavailable for use such S/w is called a data dictionarysystem(DDS).DDSs can be acquired as separate S/W

packages or as DBMSs and computer aided S/Wengineering tools.

3. A good data dictionary would ensure consistentdefinitions of data across different databases,and if

there were a change to the data ,it would also


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Benefits of databasemanagement system

Reduced programming cost

Reduced Development and

implementation timeReduced program and file managementcosts.

Reduced data redundancy

Increased flexibility


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Language

Two languages are used to communicatewith data base are:

1. Data description Language(DDL)2. Data manipulation Language(DML)

r


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rLanguage(DDL)

It is used to create and describe the data anddefine the schema in a DBMS

It serves as an interface for applicationprograms that use the data.Once the data

dictionary has been created its definition must bentered into the DBMS.

For example,if a payroll program needs the

employment number of an employee the DDLdefines the employment number and the otherdata in the database and acts as an interfacebetween the payroll program and the files that

contain the employment number


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Structured Query Language

It is a non procedural language exclusivelydeals with data:

Data integrity

Data manipulationData access

Data retrieval

Data queryData security


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SQLIt allows the user to access the data from the

databases to specific queries,both onmainframes and on PCs.Here users cantransform their experience from one database

system to another without going into muchdetail.

There are four basic operation in SQL

1. Select2. Update

3. Insert

4. And delete


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Select statement enables users to query the database forspecific information

Update statement allow users to update the data.

Insert statement new data in the existing database.

Delete statement delete existing data from the database

Two types of question s can be asked by users in SQL:

-Static Question & dynamic Question

Static questions are routine and standardize and oncedefined,can be used repeatedly or generatingweekly,monthly and quarterly reports, S/W packagesgenerating static questions are sometimes referred to asreport writers.

Dynamic questions are ad hoc and specific to thedecision maker.

Characteristics of DBMS


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Characteristics of DBMSThe capability to store large amounts of datanecessary for users needs.They are stored ondirect accessible devices for on-line support.

The capacity to interrogating data files,retrievingand modifying data and recording the changes

The data are combined to form operational unitsto minimise the duplication of data and increaseaccess to all data in the database.

The control in the systems limits the access to thedatabase files and builds the confidentiality of alldata in these files.

Objectives of DBMS


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Objectives of DBMSProvide for mass storage of relevant data.

Make access to the data easy for the userProvide prompt response to user requests for data.

Make the latest modifications to the data baseavailable immediately

Eliminate redundant Data

Allow for multiple users to be active at one time

Allow for growth in the database system

Protect the data from physical harm andunauthorised access


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Major uses of DBMS

The four major uses of a DBMS packageare:

1. Database interrogation and reporting(forend users)

2. Application development(for end users andprogrammers)

3. Database access(for end users andinformation service staff)4. Database creation and modification(for end

users and database administrators)


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Data Independence

The ability to modify a schemadefinition in one level without affectinga schema definition in the next higherlevel is called data independence.

There are two levels of dataindependence

Physical data independenceLogical data Independence


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Physical data independence

It is the ability to modify the physicalschema without causing applicationprograms to be rewritten.Modifications

at the physical level occasionallynecessary in order to improveperformance.

L i l d t I d d


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Logical data Independence

It is the ability to modify the conceptual schemawithout causing application programs to berewritten.Modification at the conceptual level arenecessary whenever the logical structure of thedatabase is altered(addition of money-market

accounts in banking system).It is more difficult toachieve than physical data independence sinceapplication programs are heavily dependent onthe logical structure of the data they access.Theconcept of DI is similar in many respects to theconcept of abstract data types in modern PLs .Both hide implementation details from theusers.This allows users to concentrate on thegeneral structure rather than low level

implementations details.


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Data base BasicData items:-It is the smallest unit of data that

has meaning to its user .The data item issimply known as the field in dataprocessing.It may be treated as a moleculeof the database.For example a student name

in a database is called as a data item.Thedata item could occasionally be furtherbroken down is called atomic level forprocessing purposes.For example,a data item

such as a data would be a composite valuecomprising the date,day and year.Forexample your registration number etc.

In the organisation ,each department is

responsible to find out its own way of-


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Entities

All the real world object such as anemployee, a component in an inventory

or a space or it may be intangible suchas a even,a job description,identificationnumbers.All such items about whichrelevant information is stored in thedatabase are called Entities.


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Attributes

An attribute may be expressed as a numberor as a text.It may even be a scannedpicture,a sound sequence,a moving picturewhich is now possible in multimedia database

Data processing normally concern with acollection of similar entities and records

information about the same attributes of eachof them

Schema


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SchemaA schema is a logical database description andis drawn as a chart of the types of data that areused .It gives the names of the entities andattributes and specify the relationship betweenthem.It is a frame work into which the dataitem can be fitted.Like an information display

system such as that giving the arrival anddeparture time at airport and railwaystations,the schema will remain the samethough the value displayed in the system will

change from time to time.The relationshipbetween the entities occurring in the schemamay be one-to-one or one-to-many or many tomany or conditional.That means it is an overall

chart of all the data item type and record types


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Subschema

The term subschema refers to the sameview but for the data-item types and

record type which are used in aparticular user.Therefore many differentsub-schemas can be derived from oneschema

Analysis between schema and


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Analysis between schema andsub schema

If schema represent a road map ofDelhi showing the major historical sites

,educational institutions,railwaystations,roadway stations and airports,asubschema could be a similar mapshowing one route each from therailway station or the airport to IGNOUcampus at Maidan Garhi


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A general model of a database system

External schema

User view User viewUser view

Conceptual Schema

Internal Schema

Stored data

Three views of data


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Three views of dataDBMS is a collection of interrelated files and a set

of programs that allows several users to access

and modify these files.The concern for efficiently leads to the design of

complex data structure for the representationof data in the data base.As the database

system are often used by non computerprofessionals,this complexity must be hiddenfrom database system users. This is done bydefining levels of abstract as which thedatabase may be viewed,there are threeviews.

1. Logical or External view2. Conceptual view

3. Internal or Physical view


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External view or logical view

It is the highest level of abstraction asseen by a user

This level of abstraction describes onlythe part of entire database.


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Conceptual view

This is the next higher level of abstractionwhich is the sum total of users views.Thislevel describes what data are actually stored

in database.This level contains information about entiredatabase in terms of a small number ofrelatively simple structure.

It represents the entities and thererelationships.

It contains integrity rules and authorizationrules,but it does not contain informationabout how the data items are stored


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Internal View

This is the lowest level of abstraction atwhich one describes how the data are

physically stored And how we canaccess it.

It includes information on ordering of

records,block sizes,storage indexes,useof pointers,and access strategies beingused.

D t B Ad i i t t


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Data Base AdministratorA person who is having central control over

the data and the programs.Functions of DBA

1. Schema definition,2. Storage structure and access method

definition,3. Schema physical organisation for data

access,

4. Integrity constraint specification.5. Back up and restore database6. Monitor database performance and

efficiency.

File management vs database management


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File management vs. database management

Topic File Management Databasemanagement

Data redundancy May have highdegree of dataredundancy

Has a low degreeof dataredundancy

DataIndependence

Recognition ofrecord format or

access methodmeans theapplication has tobe changed

Similarrecognition has

little or no impacton application

ApplicationMaintenance Highermaintenance cost Low maintenancecost

Integrity controls Usually providedby programmer

Provided byDBMS

UnanticipatedQueries A customprogram has to A query languagecan be used

on


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on .Datarelationship

Handled byapplicationsif at all

An integralpart of DBMS

Overhead Little CPUand Storage

overhead

Moreprocessing

power andstorage isneeded

Databaseownership

Applicationsmay havetheir ownprivate data

All databelongs tothe DBMS

cont


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cont

DBA Not needed Needed tocoordinate and

resolve theneeds of theusercommunity

Availability oftrainedprogrammers

Mostprogrammersare trained touse filemanagement

The averageprogrammerneeds to betrained to usedatabasemanagement

Databasedesign

Data files maybe designed as

needed

More time andeffort is spent

to develop agood databasedesign

D t d l


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Data models

A data model is a collection of concepts that

can be used to describe the structure of adatabase.By structure of a database we meanthe data types,relationships and constraintsthat should hold on data.

Most of the data models also include a set ofbasic operations for specifying retrievals andupdates on the database.

A database model is the method of organizingdata and represents the logical relationshipamong data elements in database .

D t M d l


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Data Models

Data model is of three types1. Object based logical model:ER

model,Object oriented model,binary

model,Semantic data model,infological model,functional data model

2. Records based logicalmodels:Relational,Network,Hierarchical

3. Physical data model:Unifying


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Types of data model

Hierarchical Model

Net work ModelRelational model


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Types of Relationship

One-to-one:This relationship indicates aunique relation between two entities(student-regd-no,person and employment no.)

One-to-many:Here an entity can havemultiple relationships with other entities inthe database(Air bus and passengers,teacherand student)

Many-to-many:Here every entity can berelated to a number of entities.(teachers andstudents).

of database processing system in banking


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Bank database

DBMS

Operating System

Application Program

Banking Service data model

Installment loan

data modelChequing and

Savings data model

Chequing

Application

Installment loan

ApplicationSaving

Application


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It helps to establish explicit or logicalrelationships among various data elements of

multiple files and arrange the elements in ahierarchy.

Each box is a record,it is also termed asnode.

In this model each record in one level can berelated to multiple records on the next-lowerlevel.

A record that has a subsidiary records is

callec the parent and the subsidiary recordsare called children.

It follows 1:M relationship with other dataelements in the database

Schematic of a hierarchical tree structure


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Entity type

Record type

Entity type

The above figure provides the hierarchical model


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Here link fields establish the explicit relationships.

The links are represented by thin lines that

connect data elements of the various records inthe lower portion.

Once a sales person record is retrieved the link inthat record can lead to another record i,e

logically related to that salesperson.A link field inthe second record leads to a 3rd record,and so oncreating a chain through an entire set of file.

The system retrieve records from the hierarchy

through pointers,which are pieces of data thatidentifies the link between different records.Thedata nodes in this are linked to one anotherthrough a series of pointers,one of which isattached to the end of each record in the

database

Advantage Disadvantage


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Advantage DisadvantageWell suited for

modelinghierarchical data.

Top-down naturemakes

programmingefficient.

Based on one-way access fromsuperiors to subordinates.

Not suited for manyto-manyrelationships.

Difficult to inert subordinate recordswithout superior records.

Deleting superiors logically deletessubordinates.

Difficult to update record stored inmultiple locations.

Not suited for databases whererelationships change.

Network Model


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Network ModelIn this model,each record in a database canhave multiple parents.

It maintain Many-to-Many(M:M) relationship

In network model,databases can betranslated from hierarchical form to network

form and vice-versa.Data elements are linked through pointers.

In this model a child can have a number ofparents,where as in a hierarchical model a

child can have only one parent.Like hierarchical model the records are notlimited to only one superior.

A record may have many superior records

and many subordinate records.

Network Model


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Network Model

It allows entry into a database at multipoint

A group of interconnected nodes is called anetwork.

A subway map is an example of a

network.The subway stations are thenodes,and the tracks are the interconnectionsor network.

A common approach is multi

pointers,especially with a link node recordrepresenting the connection between twoentities.

Advantages Disadvantages


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Advantages DisadvantagesIt promotes flexibilityand data

accessibility,since dataelements at a lowerlevel can be accessedwithout accessing the

data elements abovethem.

It is efficient ,easy tounderstand,and can beapplied to many realworld problems thatrequire routinetransaction.

It is complex to designand develop

It requires that therelationships among alldata elements to bedefined before

development starts,andchanges often demanda major programmingefforts

For large database

,operation andmaintenance of thenetwork model aretime-consuming andexpensive

Relational Model


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Relational ModelIn relational model , data is represented

using two-dimensional tables,called relationof flat files

The flat files are made up of columns androws.

Each column represents a field,also referredto as an attribute.

Each row represent a record , also referred as

a tuple.It is well suited for business needs because oftheir flexibility

Relational Model


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Relational ModelRelational databases use three fundamentaloperations:

SELECT

PROJECT

JOIN

The select operation is used to selected therequested query.

The project operation creates a subset ofcolumns designed to meet the information

needs of the user.The JOIN operation joins or links two or moretables ,if the information requested by theuser is not found in one table

Example:MS Access,dbase IV,DB2

Advantages Disadvantages


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Advantages DisadvantagesQuery languages allow easeof use.

It can relate data in a tableas long as the two tablesshare at least one commonattribute.Thats why mostcommercial databases for

microcomputers use relationaldatabase

It enables a computer systemto accommodate a variety offile inquiries in an efficientmanner.

No need to know the innerstructure of the database

Data independence allow easy

structure modification

Query languagesconsume processing

time and memory

Data must be related toact upon

Set processing is not

suite3d to conventionalPLs.

Command affectsystem performance

Relational Database


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Relational Database

A DBMS can be regarded as relational only

if it obeys the following three rules.1. All information must be held in tables

2. Retrieval of this data must be possible

using the following types of operationSelect, Join,Project

3. A relationship between data must be

represented explicitly in that data itself.


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Aims of Relational Database

1. Performance

2. The ability to distribute data.

3. The ability to handle enormousquantity of data


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Distributed Processing

It refers to an architecture in which adatabase resides on a different machine tothe user process accessing it.

To put this in a different way,the front andback end processes are on differentmachines.Such a machine will obviouslynecessitate some form of communicationcapability between the machine and depends

entirely on a complex logical and physicalseparation between the front and back endprocesses and processing

Distributed database


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Distributed database

A distributed data system is a collection of sites

or connected by communication lineswhereby:

1. Each participating node houses a relational

database2. These databases are themselves fully

functional within their own location.

3. A logical global distributed database isdefined incorporating elements of each ofthe participating databases in order toevaluate a single occurrence of a database.

Normalisation


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NormalisationIt is the processes of simplifying the relationshipbetween data elements in a record.Throughnormalization, a collection of data in a recordstructure is replaced by successive recordstructures that are simpler and more predictableand therefore more manageable.The reasons whyit is carried out are:

1. To structure the data to maintain the data an itsrelationship.

2. To permit simple retrieval of data in response toquery and report requests.

3. To simplify the maintenance of the data throughupdated inventories and deletions.

4. To reduce the need to restructure or reorganizedata when application requirements arise.

Degree of Normalisation


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Degree of Normalisation1NF(First Normal Form)

2NF(Second Normal Form)3NF(Third Normal Form)

BCN(Boyce-codd Normal Form)

4NF(Fourth Normal Form)5NF(Fifth or Projection-Join NormalForm)

1NF(First Normal Form)


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1NF(First Normal Form)

This is the lowest level of normalization.Arelation is said to be in 1NF if there will

be no composite attributes,and everyattributes is single and describes oneproperty.

2NF(Second Normal Form)


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2NF(Second Normal Form)A relation is said to be in 2NF if it is in 1NFand non-key attributes are functionally

dependent on the key attribute(S).Further,ifthe key has more than one attribute then nonon key attributes should be functionallydependent upon a part of the key attributes.

An attribute is a non-key if it is not part ofthe primary key.

An attribute is functionally dependent on akey if the attribute contains only one value

which depends on that key .For eg:theattribute SALARY contains only one valuewhich depends on the key NAME.

3 ( hi d l )


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3NF(Third Normal Form)

Data is in 3NF if and only if it is in 2NF and every non-key

attribute is non-transitively dependent on the primary key.A3NF will be needed where all attributes in a relation tuple arenot functionally dependent ,then there will be unnecessaryduplication of data.The purpose of 3NF is to ensure that

attributes directly belong to the entity.Transitivity is a mathematical principle that states

If a relation is true between the first value and thesecond,and between the second and the third, then the

relationship must also be true between the first and the third.Examples If AC

If A=B and B=C,then A=C

Boyce-cod Normal form


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Boyce cod Normal form

When a relation has more than one possiblekey and the composite keys have a common

attribute and if an attribute of a compositekey is dependent on an attribute of the othercomposite key,a BCNF is need.For example

Professor(professor code,Dept,HOD,PercenttimeIt is assumed that

A professor can work in more than one

departmentThe percentage of time he spends in eachdepartment is given

Each department has only one HOD


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Fourth and Fifth Normal form

When attributes in a relation havemultivalued dependency, further

normalization to 4NF and 5NF arerequired

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