QUESTION BANK DEPARTMENT: CSE SEMESTER: IV SUBJECT … · QUESTION BANK DEPARTMENT: CSE SEMESTER:...

R. Loganathan, AP/CSE. Mahalakshmi Engineering College, Trichy

QUESTION BANK

DEPARTMENT: CSE SEMESTER: IV

SUBJECT CODE / Name: CS2255 – DATABASE MANAGEMENT SYSTEM

UNIT – I

PART -A (2 Marks)

1. What is DBMS and what’s the goal of it?

DBMS is a collection of interrelated data and a set of programs to access thatdata. The goal is to provide

the environment that is both convenient andefficient to use in retrieving and storing data base information.

2. What are the advantages of DBMS?(A.U May/June 2007)

• Centralized Control• Data Independence allows dynamic change and growth potential.

• Data Duplication is eliminated with control Redundancy. • Data Quality is enhanced.

3. What are the Disadvantages of DBMS?

• Cost of software, hardware and migration is high. • Complexity of Backup• Problem associated with

centralization.

4. What are the disadvantages of File Systems?

• Data Redundancy and Inconsistency.• Difficulty in accessing data.• Data Isolation

• Integrity problems• Security Problems• Concurrent access anomalies

5. Define Entity, Entity Set, and extensions of entity set. Give one example for each.

• Entity – object or thing in the real world. E.g., each person, book, etc.

• Entity set – set of entities of the same entity that share the same properties or attributes.

E.g., Customer, loan, account, etc

• Extensions of entity set – individual entities that constitute a set. Eg.individual bank customers

6. Define and give examples to illustrate the four types of attributes in database.

• Simple and Composite attribute_ Simple (address)_ Composite (street, city, district)

• Single-valued and multi-valued attribute

Single-valued (roll no)

Multi-valued (colors = {R, B, G})

• Null attribute

No values for attribute

• Derived attribute


Age derived from Birth date

7. Define relationship and participation.(A.UMay/June 2008)

• Relationship is an association among several entities.

• Association between entity sets is referred as participation.

8. Define mapping cardinality or cardinality ratio.

Mapping cardinality or cardinality ratio is the way to express the number of entities to which another

entity can be associated through a relationship set. These are most useful in describing binary relationship

sets.

9. Explain the four types of mapping cardinality with example.(A.UNov/Dec 2006)

For a binary relationship set R between entity sets A and B, the mapping cardinality must be one of the

following: (Draw the diagrams also)

• One-to-one

An entity in A is associated with at most one entity in B and an entity in B is associated with at most one

entity in A. E.g., Roll no entity in Student info entity set and marks details entity set.

• One-to-many

An entity in A is associated with any number of entities in B. But an entity in B is associated with at most

one entity in A. E.g., one customerwith many loans.

• Many-to-one

An entity in A is associated with at most one entity in B. But anentity in B can be associated with any

number of entities in A. E.g., streetand city associated to a single person.

• Many-to-many

An entity in A is associated with any number of entities in B. Butan entity in B can be associated with any

number of entities in A. E.g.,same loan by several business partners.

10. Differentiate total participation and partial participation. (i.e., write Definition andExample

with illustration)

• Total – participation of an entity set, E in relationship, R is total if everyentity in E participates in at

least one relationship in R. E.g., loan entity set.

• Partial – if only some entities in E participate in R. E.g., payment weakentity set.

11. Define E-R diagram.(A.UNov/Dec 2007)

Overall structure of a database can be expressed graphically by E-Rdiagram for simplicity and clarity.

12. Define weak Entity set. Give an example and explain why it is weak entity set.

• Entity set with no sufficient attributes to form a primary key’s Payment entity set is weak since

duplication exists


13. Define discriminator or partial key of a weak entity set. Give example.

Set of attributes that allow distinction to be made among all those entitiesin the entity set that depends on

one particular strong entity. E.g., payment no inpayment entity set. It is also called as partial key.

14. Explain Referential Integrity.(A.UNov/Dec 2008)

Referential Integrity means relationship between tables. Foreign keys areused. Foreign key is the column

whose values are derived from the Primary keyof the same or some other table.

Format for creating a foreign key is given below.Syntax: create table <table name> (column name data

type (size) constraintconstraint name references parent table name);

15. Define Instances and schemas.

Instances: The collection of information stored in the database at a particular momentis called the instance

of the database.

Schemas: The overall design of the database is called the schema of the database.

16. Define and explain the two types of Data Independence.(A.UNov/Dec 2011)

Two types of data independence are

i. Physical data independenceii. Logical data independence

Physical data independence:

The ability to modify the physical schema without causing applicationprograms to be rewritten in the

higher levels. Modifications in physical leveloccur occasionally whenever there is a need to improve

performance.

Logical data independence:

The ability to modify the logical schema without causing applicationprograms to be rewritten in the

higher level (external level). Modifications inphysical level occur frequently more than that in physical

level, whenever there isan alteration in the logical structure of the database.

17. Define transaction.(A.UMay/June 2007)

A transaction is a collection of operations that performs a single logicalfunction in a database application.

Each transaction is a unit of both atomicity andconsistency. Properties of transaction are atomicity,

consistency, isolation, anddurability.

18. Define the type types of DML.(A.UNov/Dec 2010)

Two types:• Procedural DML• Non-procedural DML

Procedural DML:

It requires a user to specify what data are needed and how to get thosedata.

Non-Procedural DML:

It requires a user to specify what data are needed without specifying howto get those data.


19. List out the functions of DBA.

• Schema definition• Storage structure and access-method definition• Schema and physical modification•

Granting of authorization for data access• Integrity constraint specification

20. What is the need for DBA?

The need of DBA is to have central control of both the data and theprograms that access those data. The

person who has such central controlover the system is called the DataBase Administrator.

21. Explain DML pre-compiler.

DML precompiled converts DML statements embedded in an applicationprogram to normal procedure

calls in the host language. The precompiledmust interact with the DML compiler to generate the

appropriate code.

22. Define file manager and buffer manager.(A.UNov/Dec 2009)

File manager:

File manager manages the allocation of space on disk storage and the datastructures used to represent

information stored on disk.

Buffer manager:

Buffer manager is responsible for fetching data from the disk storage intohis main memory, and deciding

what data to cache in memory.

23. Define Data Dictionary.(A.U May/June 2007)

DDL statements are compiled into a set of tables that is stored in a special file called data dictionary. Data

dictionary contains the meta-data, which in turn isdata about the data.

24. Give the syntax for creating the table with composite primary key.

Multicolumn primary key is called composite primary key.

Syntax: create table <table name>(columnname1 data type (size), columnname2data type (size),

constraint name primary key (columnname1, columnname2));

25. Write a query to display loan number, branch name where loan amount is between

500 and 1000 using comparison operators.

Query: select loan no, branch name from loan where amount>=500 and amount<=1000;

26. Find the names of all branches with customers who have an account in the bank

And who live in the Harrison city using Equip-join.

Query: select branch name from customer, account, depositor wherecust_city='Harrison' and

customer.cust_name=depositor.cust_nameanddepositor.acc_no=account.acc_no;

27. Find the names of all branches with customers who have an account in the bank

And who live in the Harrison city using Sub-Queries.


Query: select branch name from account where acc_no in (select acc_no from depositor where

cust_name in (select cust_name from customer wherecust_city='Harrison'));

PART-B

1. Explain DBMS System Architecture (Apr/May 2011)

DATABASE SYSTEMARCHITECTURE

Adatabasesystemispartitionedintomodulesthatdealwitheachoftheresponsibilitiesofthe

overallsystem. The functional components of adatabasesystem can bebroadlydivided into

StorageManager

QueryProcessor

Thedatabasesystemarchitectureisinfluencedby theunderlyingcomputerarchitecture.Thedatabase

systemcanbecentralizedorclientserver.Database systems arepartitionedintotwoorthree parts.In

twotierarchitecture,theapplicationispartitionedintoa componentthatresidesattheclientmachine and

invokes database functionality at the server machine through query language. Application

programinterface standardslike ODBCandJDBCare usedfor interactionbetweentheclientandthe

server.Inthreetierarchitecture,theclientmachinesactasafrontendanddonotcontainany direct databasecalls.

The clientendcommunicateswiththe applicationservers throughinterface.The applicationserver interacts

with databasesystem to access data. Thebusiness logic of application says what actions to be carried

out underwhat condition.Threetier is more appropriate forlargeapplications.

Two tierarchitecture


Three tierarchitecture

1 Storage Manager

A storage manager isa programmodule thatprovidesthe interfacebetweenthe lowleveldata

stored in the database and the application programs and queries submitted to the system.

Thestoragemanager is responsible forthe interaction with the filemanager.

ThestoragemanagertranslatesthevariousDML statementsintolow-levelfilesystem

commands.Thus,thestoragemanagerisresponsibleforstoring,retrieving,andupdating datain the

database.


Figure1.5.Database SystemStructure


Components of thestoragemanager are:

Authorizationandintegritymanager:Ittestsforsatisfactionofvariousintegrityconstraints and

checks the authorityofusers accessingthe data.

Transactionmanager:It ensures that thedatabase remains ina consistentstatedespitesystem

failures, andconcurrent executions proceed without conflicting.

Filemanager:Itmanagestheallocationofspaceondiskstorageandthedatastructuresused to

represent information stored on disk.

Buffermanager:Itisresponsibleforfetchingdatafromdiskstorageintomainmemoryand

todecidewhatdatatocache inmainmemory.Itenablesthedatabasetohandledatasizesthat are

muchlargerthanthesize ofthemainmemory.The storage managerimplementsseveral data

structuresas part ofphysical system implementation.

Data files: which storethe databaseitself.

Datadictionary:Itcontainsmetadatathatisdataaboutdata.Theschemaofatableisan

exampleofmetadata.Adatabasesystemconsultsthedatadictionary before readingand

modifyingactual data.

Indices:Which provide fast access to data items thathold particularvalues.

2 Query Processor

Thequeryprocessorisanimportantpartofthedatabasesystem.Ithelpsthedatabasesystemto

simplifyand facilitate access to data. Thequeryprocessorcomponents include:

DDLinterpreter,whichinterpretsDDLstatementsandrecordsthedefinitionsinthedata dictionary.

DMLcompiler,whichtranslatesDMLstatementsinaquerylanguageintoanevaluationplan

consistingof low-level instructions that thequeryevaluation engine understands.

A querycan betranslatesinto anynumberof evaluations plans that allgivethe same result.

TheDMLcompileralsoperformsqueryoptimization,thatis,itpicksupthelowestcost evaluation plan

fromamongthealternatives.

Query evaluation engine, which executes low-level instructions generated by the DML

compiler.

2. Explain E-R Model in detail with suitable example. (Nov/Dec 2009)

TheE-R data modelconsiders the real world consistingof aset of basicobjects, calledentities,

and relationships among theseobjects.


TheE-R data modelemploys threebasic notions:

Entitysets

Relationship sets

Attributes

Entity Sets

Anentityis‗thingor‗objectintherealworldthatisdistinguishablefromallother objects.

For example, each person is an entity.

Anentityhasasetofproperties,andthevaluesforsomesetofpropertiesmayuniquely

identifyanentity.

Forexample,acustomerwithcustomer-idpropertywithvalueC101uniquelyidentifies that

person.

Anentitymaybeconcrete,suchaspersonorabook,oritmaybeabstract,suchasaloan, oraholiday.

Anentitysetisasetofentitiesofthesametypethatsharethesameproperties,or attributes.

Forexampleallpersonswhoarecustomersatagivenbankcanbedefinedasentityset customer.

Theproperties that describe an entityare calledattributes.

Relationships andRelationships sets

Relationshipis an association amongseveral entities.

Relationship setis a set of relationshipsof thesametype.

Theassociationbetweenentity setisreferredtoasparticipation.Thatis,theentity setsE1, E2, . .

.,En participate inrelationship set R.

Recursiverelationshipset:Sameentity setparticipating inarelationshipmorethanoncein

adifferent role is calledRecursive relationship set.

The attributes of entitiesin Recursive relationship set is calleddescriptive attributes.

Types ofrelationships

Unaryrelationship:Aunaryrelationshipexistswhenanassociationismaintainedwithin

asingleentity


Figure1.6.Association betweentwo objects ofthesamelist.

Binary relationship: Abinaryrelationship existswhen two entities are associated.

Figure1.7. Binary Relationshipbetween publisherand book

Ternary relationship: A ternary relationship exists when there are three entities

associated.

Figure1.8.E-R diagramwith Ternary relationship

Quaternaryrelationship:Aquaternaryrelationshipexistswhentherearefourentities

associated.

Figure1.9.E-R diagramwithQuaternary relationship


Thenumberofentitysetparticipatingina relationship is calleddegreeof the relationship set.

Binaryrelationship set is of degree2; a tertiaryrelationship set is of degree3.

Entityrole:Thefunctionthatanentityplaysinarelationshipiscalledthatentity‘srole.A

roleis one end ofan association.

Figure1.10. Entity roleis Employee

Attributes

Theproperties that describes an entityiscalled attributes.

The attributes of customer entitysetare customer_id, customer_nameandcity.

Eachattributes hasasetofpermitted values called the domain or value set.

Eachentitywillhavevalue forits attributes.

Example:

Customer Name John

CustomerId 321

Attributes are classified as

Simple

Composite

Single-valued

Multi-valued

Derived

Simple attribute:

This typeofattributes cannot be divided into sub parts.

Example:Age, sex, GPA

Compositeattribute:

This typeofattributes Can besubdivided.

Example:Address:street, city, state, zip


Single-valuedattribute:

This typeofattributes can haveonlyasingle value

Example: Social securitynumber

Multi-valuedattribute:

Multi-valued attributeCan havemanyvalues.

Example: Person mayhaveseveral collegedegrees, phonenumbers

Derived attribute:

Derived attributeCanbecalculated or derivedfrom other relatedattributes or entities.

Example:Agecan bederived from D.O.B.

Storedattributes:

The attributesstoredina database are calledstoredattributes.Anattribute takesa nullvalue whenan

doesnothaveavalueforit.Nullvalues indicatethevaluefortheparticularattribute does not exists or

unknown.

E.g.:Middlenamemaynotbepresentforaperson(nonexistencecase),Apartmentnumber

maybemissingor unknown.

CONSTRAINTS

AnE-Renterpriseschemamaydefinecertainconstraintstowhichthecontentsofadatabase system

must conform.

Threetypes of constraints are

Mappingcardinalities

Keyconstraints

Participation constraints

Mappingcardinalities

Mappingcardinalitiesexpressthenumberofentitiestowhichanotherentitycanbe associated

viaa relationship set

Cardinalityin E-R diagram that is represented bytwo ways:

Directed line( )

Undirected line( )


There are4categories ofcardinality.

Onetoone:AnentityinAisassociatedwithatmostoneentityinB,andanentityinBis associated with at

most one entityin A.

Figure1.11. One to one

Example:Acustomerwithsingleaccountatgivenbranchisshownbyone-to-onerelationship as

givenbelow

Figure1.12. One to onerelationship betweencustomerandaccount

One-to-many:AnentityinAisassociatedwithanynumberofentities(zeroormore)inB.

An entityin B, however,can beassociated with atmostoneentityin A.

Figure1.13. Onetomany

Example:Acustomerhavingtwo accountsat agivenbranchisshownbyone-to-many relationship

as given below.


Figure1.14. Onetomany relationshipbetweencustomerandaccount

Many-to-one:AnentityinAisassociatedwithatmostoneentityinB.AnentityinB, however,can

beassociated with anynumber (zero or more) ofentities in A.

Figure1.15.Many to one

Example:Manyemployeesworksforacompany.Thisrelationshipisshownbymany-to-one as

givenbelow.

Keys

Figure1.16.Many to one relationshipbetwennEmployees andCompany

A keyallows us to identifyaset of attributesand thus distinguishes entities from each other.

Keysalsohelpuniquelyidentifyrelationships,andthusdistinguishrelationshipsfromeach other.


Table 3.1 List ofKeys

Key Type Definition

Superkey

Anyattributeorcombinationofattributesthat

uniquelyidentifiesarowinthetable.Example:

Roll_Noattributeoftheentity set‗student‘

distinguishesonestudententity fromanother.

Customer_name, Customer_id togetherisa

Super key

CandiateKey

MinimalSuperkey.Asuperkeythatdoesnot

contain asubset ofattributes that is itself a

superkey.Example: Student_name and

Student_street,aresufficient to uniquely

identify one particularstudent.

PrimaryKey

Thecandidatekey selectedtouniquely identify

all rows. It shouldbe rarely changed and

cannotcontainnullvalues.Example:Roll_No is

aprimaryset of‗student‘ entityset.

Foreign Key

Anattributeinonetablethatmusteithermatch

the primarykeyofanother table orbenull

Example: Consider in the staff relation the

branch_noattributeexiststomatchstafftothe

branchofficetheyworkin.Inthestaff relation,

branch_no is foreign key.

SecondaryKey Anattributeorcombinationofattributesused

tomakedata retrieval moreefficient.

Many-to-many:AnentityinAisassociatedwithanynumber(zeroormore)ofentitiesinB, and an

entityin Bis associated with anynumber (zero ormore) ofentities in A.


Figure1.17.Many to Many

Example:Employeeworks on numberofprojects and project is handledbynumberof

employees.Therefore,therelationshipbetweenemployeeandprojectismany-to-many as shown

below.

Figure1.18.Many to Many relationshipbetweenEmployeeand project

ParticipationConstraint

Participation can bedivided into two types.

Total

Partial

IfeveryentityintheentitysetEparticipatesinatleastonerelationshipinR.Then participation is

called Total Participation

If only some entities in the entity set E participate in relationships in R. Then the

participation is called Partial Participation.


3. Explain about Entities-Relationship(E-R)Diagrams in details.

E-R diagram can express theoveralllogical structureof adatabasegraphically. E-

R diagramconsistsof the followingmajor components:

E-R diagramNotations.


E-R Diagramwith composite,multivalued, andderivedattributes

DoublelinesareusedinanE-Rdiagramtoindicatethattheparticipationofanentity setina

relationshipsetistotal; thatis,eachentityintheentitysetoccursinatleastone relationshipin that

relationship set.

ParticipationofanEntity Set in aRelationship Set

Thenumberoftimeanentity participatesinarelationshipcanbespecifiedusingcomplex

cardinalities.Anedgebetweenanentity setandbinaryrelationshipsetcanhaveanassociated

minimum and maximum cardinalityassigned in the form of l andh.

l -Minimum cardinality

h -Maximum cardinality


A minimumvalue of1 indicates total participationof the entityset in the relationshipset. A

maximum valueof 1indicates that the entityparticipates in at most onerelationship.

A maximum value* indicates no limit.

A label 1... onan edgeis equivalent to adouble line.

Many to one relationshipbetweeencustomerandloan

Strong andWeakentity sets

Anentitysetmay nothavesufficientattributestoformaprimary key.Suchanentity setis

termedaweakentityset.Anentity setthathasaprimary keyistermedastrongentityset. Weakentity

setisassociatedwithanotherentitysetcalledtheidentifyingorownerentity set.

ie,weakentitysetissaidtobeexistencedependentontheidentifyingentity set.Identifying entity

setissaidtoowntheweakentity set.Therelationshipamongtheweakandidentifying entityset is

called theidentifyingrelationship.

Weakentity set


Extendede-rfeatures

ERmodelthat issupportedwiththeadditional semanticconceptsiscalledtheextendedentity

relationship model or EER model. EER model deals with

Specialization

Generalization

Aggregation

Specialization

Theprocessofdesignatingsubgroupingswithinanentity setiscalledSpecialization.

Specializationisatop-downprocess.Consideranentity setperson.Apersonmay befurther

classifiedasoneofthefollowing-CustomerandEmployee.Allpersonhasa setofattributesin

commonwithsomeadditionalattributes.Specializationisdepictedby atrianglecomponent

labeledISA.ThelabelISAstandsfor isforexample,thatacustomerisperson.TheISA relationship

mayalso bereferred toas asuperclass-subclass relationship.

Example forspecializationandgeneralization


Generalization

Generalizationisasimpleinversionofspecialization.Generalizationistheprocessofdefining

amoregeneralentity typefromasetofmorespecializedentitytypes.Generalizationisa bottom-

upapproach.Generalizationresultsinthe identificationofageneralizedsuperclass from theoriginal

subclasses.

AttributeInheritance

Apropertyofthehigher-andlower-levelentitiescreatedbyspecializationandgeneralization

isattributeinheritance.Theattributesofthehigher-levelentity setsaresaidtobeinherited by

thelower-levelentitysets.Forexample, customerandemployeeinherittheattributesof person.

Theoutcomeof attributeinheritanceis:

Ahigher-levelentitysetwithattributesandrelationshipsthatapplytoallofitslower- level

entitysets.

Lower-levelentitysetswithdistinctivefeaturesthatapplyonlywithinaparticular lower-level

entityset

Ifanentitysetisinvolvedasalower-levelentitysetinonly oneISArelationship,then

theentitysethassingleinheritance.Ifanentitysetisinvolvedasalower-levelentity

setinmorethanoneISArelationship,thentheentitysethasmultipleinheritanceand the

resultingstructureissaid to bea lattice.

Constraints on Generalizations

Onetypeofconstraintdeterminingwhichentitiescanbemembersofalower-level entityset.

Such membership maybeoneof thefollowing:

Condition-defined.Incondition-definedthemembersoflower-levelentityset

isevaluatedonthebasisofwhetherornotanentity satisfiesanexplicit condition.

User-defined. User defined constraints aredefined byuser.

Asecondtypeofconstraintrelatestowhetherornotentitiesmaybelongtomorethan onelower-

levelentitysetwithinasinglegeneralization.Thelower-levelentitysets maybeoneof

thefollowing:


Disjoint. A disjointness constraintrequires that anentitybelongto no more than

onelower-level entityset.

Overlapping.Sameentitymaybelongtomorethanonelower-levelentityset within

asinglegeneralization.

Afinalconstraint,thecompletenessconstraintspecifieswhetherornotanentityinthe higher-

levelentity setmustbelongtoatleastoneofthelower-levelentity sets.This

constraintmaybeoneofthe following:

Totalgeneralizationorspecialization.Eachhigher-levelentitymustbelongtoa lower-

level entityset.It is represented bydouble line.

Partial generalizationor specialization. Some higher-level entities may not

belongto anylower-level entityset.

Aggregation

Onelimitation of theE-R model is that itcannot express relationships amongrelationships.

Considertheternaryrelationshipworks-on,betweenaemployee,branch,andjob.Now,supposewe

wanttorecordmanagersfortasksperformedbyanemployeeatabranch.Thereanotherentityset

manageriscreated.Thebestwaytomodelsuchasituationistouseaggregation.Aggregationisan

abstractionthroughwhichrelationshipsaretreatedashigher-levelentities.Inourexampleworks-on act as

high level entity.

Figure1.25.E-R diagramwith redundant relationships.


Symbols usedinE-R notations


E-R diagramwith aggregation

INTRODUCTION TO RELATIONALDATABASES

A relationaldatabase isbasedonthe relationalmodelanduses a collectionof tablestorepresent both

data and the relationship amongthose data.Itincludes DMLand DDL languages.

Tables -Each tablehasmultiple columns and each column has uniquename.

Account table

Arelationalmodelisanexampleofarecordbasedmodel.Recordbasedmodelare structuredin

fixedformatrecordofseveraltypes.Eachtablecontainsrecordofparticulartype.Eachrecord type

definesa fixednumber offieldsorattributes.The columnsofthetable correspondtothe attributeof

record type.

Data ManipulationLanguage (DML)

DMLincludes following commands

INSERT– To insert oneormorenumberof Rows.


SELECT– To displayoneor more rows.

UPDATE – Used to alterthe column values in a table.

DELETE– Used to delete oneor more rows.

Data DefinitionLanguage (DDL)

DDLincludes following commands

CREATE– Command used forcreatingtables.

DESC– Command used to viewthe table structure.

ALTER– Command used formodifyingtablestructure.

RENAME– usedto changethename ofthetable.

DROP– Command used for removinganexistingtable.

4. Explain about Data Models and its types.

Underlying structureofthedatabaseiscalledasdatamodels.Itisacollectionofconceptual

toolsfordescribing data,datarelationships,datasemantics,andconsistency constraints.Itisa wayto

describethe design ofthe database at physical, logical and view level.

Different Types OfData Models

Entityrelationship model

Relational model

Hierarchical model

Networkmodel

Object Based model

Object Relational model

Semi Structured Data model

Entity relationshipmodel

It is based on acollection ofreal world things orobjects called entities and the

relationshipamongtheseobjects.TheEntityrelationshipmodeliswidely usedindatabase design.

Relational Model

The relational model uses a collection of tables to represent both data and the

relationshipamongthosedata.Eachtablehasmultiplecolumnsandeachcolumnhasaunique


name.SoftwaresuchasOracle,MicrosoftSQLServerandSybasearebasedontherelational model.

E.g. RecordBased model.It is based onfixed format records of several types. Hierarchical

Model

Hierarchical databaseorganizedata in to a treedatastructuresuch that eachrecord type

hasonly oneowner.Hierarchicalstructureswerewidely usedinthefirstmainframedatabase

management systems.

Links arepossible verticallybut nothorizontallyordiagonally.

Advantages

High speed of access to largedatasets.

Easeof updates.

Simplicity: the design ofahierarchical databaseis simple.

Datasecurity:Hierarchicalmodelwasthefirstdatabasemodelthatofferedthedatasecurity that is

provided and enforced bythe DBMS.

Efficiency:Thehierarchicaldatabasemodelisavery efficientonewhenthedatabasecontains

alargenumber oftransactions, usingdata whose relationships are fixed.

Disadvantages

Implementation complexity

Databasemanagement problems

Lack of structural independence

NetworkModel

Themodel is based on directedgraph theory.

Thenetworkmodelreplacesthehierarchicaltreewithagraphthusallowingmoregeneral

connections amongthe nodes.

Themaindifferenceofthenetworkmodelfromthehierarchicalmodelisitsabilityto handle

many-to-many(n:n) relationship or in other words, it allows arecord to havemore

than oneparent.Example is, an employeeworking fortwo departments.


Advantages

Conceptual simplicity

Data independence

Disadvantages

Detailed structural knowledgeis required.

Lack of structural independence.

Object-Based Datamodel

Theobject-oriented model is an extension of E-R model.

Theobject-oriented model is based on a collection ofobjects.

An object contains values stored in instancevariables within theobject.

Anobjectalsocontainsbodiesofcodethatoperateintheobjectthesebodiesofcodeare called

methods.

Objectsthatcontainthesametypesofvaluesandmethodsaregroupedtogetherinto classes.

Advantages

Applications requirelesscode.

Codeis easierto maintain

Applications use morenatural datamodel.

Itprovideshigherperformancemanagementofobjectsandcomplexinterrelationships between

objects.

Object-oriented features improveproductivity.Data access is easy.

Object Relational Model

Object-relational data model combines the feature of modern object-oriented

programminglanguageswith relational databasefeatures.


Someoftheobject-relationalsystemsavailableinthemarketareIBMDB2universal

server,Oracle Corporation‘s oracle 8, Microsoft Corporations SQLserver 7and so on.

Semi StructuredDataModel

Thisdatamodelallowstheindividualdataitemsofsametypetohavedifferentsetsof attributes.

Other data modelallows aparticular typeof dataitem to havesameset of attributes.

ExtensibleMarkupLanguage (XML)is used to represent structured data.

Updateauthorization

Allows modification but notdeletion.

Deleteauthorization

Allows deletion of data.

Theusers maybe assigned with all, none or combinationofthesetypes.

TheDDL gets some input and generates some output.

This output is placed in datadictionarywhichcontains Meta data.

Databasesystem consults the Data Dictionarybeforereadingor modifyingactual data.

Metadata is dataabout data.

DataDictionaryisaspecialtypeoftablewhichcanonlybeaccessedandupdatedby

databasesystem.

Data ManipulationLanguage

Adata-manipulationlanguage(DML)isalanguagethathelpsuserstoaccessormanipulate

data.

A queryis a statementrequestingthe retrieval of information.

Theportion of DMLthatinvolves information retrieval is called as querylanguage.

There arebasicallytwo types of DML:


Procedural DMLs

User should specifywhatdata areneeded andhowto get thosedata.

DeclarativeDMLs(nonproceduralDMLs)

Usershouldspecifywhatdataareneededwithoutspecifyinghowtogetthosedata.Thisis

easierto learn and user than procedural DML.

Data manipulation that can beperformed

usingDMLare, The retrieval of information

stored in thedatabase

Theinsertion ofnew information into the database

Thedeletion of information from thedatabase

Themodification ofinformation stored in thedatabase

5. Expalin about Database UsersAndAdministrator in details.

People who work with adatabasecan becategorized as:

DatabaseUsers

Databaseadministrators

1 Database Users

There are fourtypes of databaseusers, differentiated bythewaytheyinteract with the system.

Naiveusers

Naiveusersinteractwiththesystem byinvokingoneoftheapplicationprogramsthathave

been written previously.

Naiveusersare typicalusersofforminterface,wheretheusercanfillinappropriatefields

ofthe form.

Naive users mayalso simplyreadreportsgenerated from thedatabase.

ApplicationProgrammers

Application programmers are computer professionals who write application

programs.

Rapid applicationdevelopment (RAD) tools enable the application programmer to

construct forms andreports withoutwritingaprogram.

Special types of programming languages that combine control structures with data

manipulation language.Theselanguages, sometimes calledfourth-generation


languages.

Sophisticated users

Sophisticatedusersinteractwiththesystemwithoutwritingprograms.Instead,theyform

theirrequestsin a databasequerylanguage.

Theysubmit each such queryto aqueryprocessorthat the storagemanagerunderstands.

Onlineanalyticalprocessing(OLAP)toolssimplifyanalysisanddataminingtoolsspec

ify certain kinds of patterns in data.

Specialized users

Specializedusersaresophisticateduserswhowritespecializeddatabaseapplicationsthat

do not fit into the traditional data-processingframework.

Theapplicationsarecomputer-

aideddesignsystems,knowledgebaseandexpertsystems, systems that storedatawith

complexdata types

2 DATABASE ADMINISTRATORS

Apersonwhohassuchcentralcontroloverthesystemiscalledadatabaseadministrator

(DBA).

The functions of aDBA

include:

Schemadefinition.TheDBAcreatestheoriginaldatabaseschemabyexecutingasetofdata

definition statements in the DDL.

Storagestructureand access-method

definition.

Schemaandphysical-organizationmodification.TheDBAcarriesoutchangestotheschema

and physical organization to reflect thechanging needs of theorganization.

Grantingofauthorizationfordataaccess.Bygrantingdifferenttypesofauthorization,the

databaseadministrator can regulatewhich parts ofthe databasevarious users can access.

Authorization information is kept in a special system structure that the database

system consults whenever someone attempts to access thedata in the system.

Routinemaintenance.Examplesofthedatabaseadministrator‘sroutinemaintenanceactivitie

s


are:

Periodicallybackingup thedatabase

Ensuringthat enoughfreedisk space

Monitoringjobsrunningonthedatabaseandensuringthatperformanceisnotdegradedby

veryexpensive tasks submitted bysomeusers.

Ensuringthatperformanceisnotdegradedbyveryexpensivetaskssubmittedbysome

users.

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