lec 12 client server

7/24/2019 Lec 12 Client Server

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The Client/Server DatabaseThe Client/Server DatabaseEnvironmentEnvironment

CS263 Lecture 12


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Client/Server systemsClient/Server systems

Operate in a networked environment

Processing of an application distributed between frontendclients and backend servers

!enerall" t#e client process re$uires some resource% w#ic# t#eserver provides to t#e client

Clients and servers can reside in t#e same computer% or t#e" canbe on different computers t#at are networked toget#er% usuall"&

Client ' (orkstation )usuall" a PC* t#at re$uests and uses aservice

Server ' Computer )PC+mini+mainframe* t#at provides aservice, -or ./0S% server is a database server


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Three components ofThree components of

application logicapplication logic 1, nput ' output or presentation logic component '

responsible for formatting and presenting data on t#e users

screen )or ot#er output device* and managing user input from

ke"board )or ot#er input device* 2, Processing component logic ' #andles data processing

logic )validation and identification of processing errors*%

business rules logic% and data management logic )identifies

t#e data necessar" for processing t#e transaction or $uer"* 3, Storage component logic ' responsible for data storage and

retrieval from t#e p#"sical storage devices ' ./0S activities

occur #ere


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Client/Server architecturesClient/Server architectures

-ile Server rc#itecture

.atabase Server rc#itecture

4#reetier rc#itecture

Client does

extensive processing

Client does little

processing


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File server architectureFile server architecture

4#e first client+server arc#itectures developed

ll processing is done at t#e PC t#at re$uested t#e data% ,e, t#eclient #andles t#e presentation logic% t#e processing logic and muc#

of t#e storage logic file server is a device t#at manages file operations and is s#ared b"

eac# of t#e client PCs attac#ed to t#e L5

ac# file server acts as an additional #ard disk for eac# of t#e clientPCs

ac# PC ma" be called a -4 CL54 )most processing occurs ont#e client*

ntire files are transferred from t#e server to t#e client forprocessing,


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Three problems with fileThree problems with file

server architectureserver architecture 1, 7uge amount of data transfer on t#e network% because

w#en client wants to access data w#ole table)s* transferred

to PC ' so server is doing ver" little work% network is

transferring large blocks of data and client is bus" wit#

e8tensive data manipulation

2, ac# client is aut#orised to use t#e ./0S w#en a

database application program runs on t#at PC, 4#us t#ere

is one database but man" concurrentl" running copies oft#e ./0S )one on eac# active PC* ' so #eav" resource

demand on clients


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Three problems with fileThree problems with file

server architectureserver architecture 3, 4#e ./0S cop" in eac# client PC must manage t#e

s#ared database integrit"% ,e, Client ./0Ss must

recogni9e s#ared locks% integrit" c#ecks% etc, So

programmers must be sop#isticated to recognise various

subtle conditions t#at can arise in a multipleuser database

environment% as #ave to understand overview of

concurrenc"% recover" and securit" controls and build

t#ese into t#eir application


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-ile Server rc#itecture

AT CLIENTAT CLIENT


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Database server architecturesDatabase server architectures fter t#e fileserver approac# came twotiered approac#es Client is responsible for managing user interface% +O processing logic%

data processing logic and some business rules logic )frontend programs*

.atabase server performs all data storage and access processing )backend functions* ' ./0S is onl" on server

dvantages include&Clients do not #ave to be as powerful% onl" t#edatabase server re$uires processing power ade$uate to #andle t#edatabase ' t#erefore t#e server can be tuned to optimise data processing

performance

!reatl" reduces data traffic on t#e network% as onl" t#ose records )rat#er

t#an tables* t#at matc# t#e re$uested criteria are transmitted to t#e client mproved data integrit" since it is all processed centrall"


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Stored proceduresStored procedures

4#ese are modules of code t#at implement applicationlogic% w#ic# are included on t#e database server, 4#e" #avet#e following advantages&

Performance improves for compiled S:L statements ;educed network traffic as processing moves from t#e

client to t#e server

mproved securit" if t#e stored procedure is accessed rat#er

t#an t#e data and code being moved to t#e server mproved data integrit" as multiple applications access t#e

same stored procedure

4#inner clients )and a fatter database server*


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Stored proceduresStored procedures

7ave some disadvantages&

(riting stored procedures takes more time t#an using

somet#ing like


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Database server architecture

ThinnThinnerer

clientclient

ss

DBMS onlyDBMS only

on serveron server


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Three-tier architecturesThree-tier architectures n general% t#ese include anot#er server la"er in addition to t#e client and database

server

4#is additional server ma" be used for different purposes

Often application programs reside on t#e additional server )t#e application server*

Or additional server ma" #old a local database w#ilst anot#er server #olds t#e

enterprise database Often a t#in client PC =ust for user interface and a little application processing,

Limited or no data storage )sometimes no #ard drive*


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Three-tier architecture

ThinnestThinnestclientsclients

Business rules onBusiness rules on

separate serverseparate server

DBMS only onDBMS only on

DB serverDB server


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Advantages of three-tierAdvantages of three-tier

architecturesarchitectures Scalabilit" ' middle tier can be used to reduce t#e load on a

database sever b" using a transaction processing )4P* monitor toreduce t#e number of connections to a server% and additional

application servers can be added to distribute applicationprocessing

4ec#nological fle8ibilit" ' easier to c#ange ./0S engines 'middle tier can be moved to a different platform, Simplifiedpresentation interfaces make it easier to implement newinterfaces

Longterm cost reduction ' use of offt#es#elf components orservices in t#e middle tier can reduce costs% as can substitutionof modules wit#in an application rat#er t#an a w#ole application


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Advantages of three-tierAdvantages of three-tier

architecturesarchitectures /etter matc# of s"stems to business needs ' new modules

can be built to support specific business needs rat#er t#an

building more general% complete applications

mproved customer service ' multiple interfaces on

different clients can access t#e same business process

Competitive advantage ' abilit" to react to business

c#anges $uickl" b" c#anging small modules of code rat#er

t#an entire applications


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Challenges of three-tierChallenges of three-tier

architecturesarchitectures 7ig# s#ortterm costs ' presentation component must be split

from process component ' t#is re$uires more programming

4ools% training and e8perience' currentl" lack of development

tools and training programmes% and people e8perienced in t#etec#nolog"

ncompatible standards ' few standards "et proposed

Lack of compatible enduser tools ' man" enduser tools suc#

as spreads#eets and report generators do not "et work t#roug#middletier services )see later discussion on middleware*


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Application partitioningApplication partitioning

Placing portions of t#e application code in differentlocations )client vs, server* -4; it is written, 7as t#efollowing advantages&

mproved performance mproved interoperabilit"

/alanced workloads across t#e tiers

OO development ver" suitable for t#is

5ecessar" in t#e (eb environment% in order to ac#ievedesired performance in an unpredictable distributedenvironment


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arallel computerarallel computer

architecturesarchitectures 4#e abilit" to #andle #ig# transaction volumes% comple8

$ueries and new data t"pes #as proven problematic in man"

uniprocessor environments, /ut ;./0S and S:L lend

t#emselves to a parallel environment in 2 wa"s )see following-ig,*&

1, n most $ueries% S:L acts as a nonprocedural set

processing language ' t#is means t#at $ueries can be divided

into parts% eac# of w#ic# can t#en be run on a differentprocessor simultaneousl"

2, 0ultiple $ueries can be run in parallel on parallel

processors


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!uery processing with parallel!uery processing with parallel

processorsprocessors

Parallel transactions

Parallel $uer"


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architecturesarchitectures 4ig#tl" Coupled multiprocessor s"stems #ave a common

s#ared memor" );0* among all processors% and are oftencalled S"mmetric 0ultiprocessing )S0P* arc#itectures,

7ave some advantages& Single cop" of t#e operating s"stem resides in t#e s#ared

memor"

/ottlenecks are lessened compared to uniprocessor s"stemsbecause all processors s#are all tasks

>seful for situations w#ere data must remain in memor"during processing to ac#ieve t#e desired performance level 'but potential problems of contention for t#e s#ared memor"


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architecturesarchitectures Loosel" Coupled arc#itectures% also called 0assivel" Parallel

Processing )0PP* are w#ere eac# CP> #as its own ;0

space

;e$uire a cop" of t#e operating s"stem to be resident in eac#dedicated memor"

Less problems wit# memor" contention% allows more

scalabilit" ' easier to add nodes incrementall" t#an S0P

/asicall" applications t#at #ave large tasks t#at can be dividedup and worked on simultaneousl" t#at are best suited to 0PP

arc#itectures% rat#er t#an applications t#at can benefit from t#e

use of s#ared memor"


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arallel Computer Architecturesarallel Computer Architectures

4ig#tl"coupled ' CP>s s#are

common memor" space

Loosel"coupled ' CP>s eac#

#ave t#eir own memor" space


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"iddleware"iddleware

Software w#ic# allows an application to interoperateinteroperatewit#ot#er software% wit#out re$uiring t#e user to understand andcode t#e lowlevel operations re$uired to ac#ieve

interoperabilit"(it# S"nc#ronous s"stems% t#e re$uesting s"stem waits for a

response to t#e re$uest in real time

s"nc#ronous s"stems send a re$uest but do not wait for aresponse in real time ' t#e response is accepted w#enever itis received ,

The gluegluethat holds client/server applications together


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Si# types of middlewareSi# types of middleware 1, s"nc#ronous ;emote Procedure Calls );PC* client makes calls to

procedures running on remote computers but does not wait for a response,

f connection is lost% client must reestablis# t#e connection and sendre$uest again, 7ig# scalabilit" but low recover"% largel" replaced b" t"pe2

2, S"nc#ronous ;PC ' distributed program using t#is ma" call servicesavailable on different computers ' makes it possible to ac#ieve t#is

wit#out undertaking detailed coding )e,g, ;0 in ?ava* 3, Publis#+Subscribe ' often called pus# tec#nolog"% #ere server monitors

activit" and sends information to client w#en available, t isas"nc#ronous% t#e clients )subscribers* perform ot#er activities betweennotifications from t#e server, >seful for monitoring situations w#ereactions need to be taken w#en particular events occur,


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Si# types of middlewareSi# types of middleware

@, 0essageOriented 0iddleware )0O0* as"nc#ronous '

sends messages t#at are collected and stored until t#e" are

acted upon% w#ile t#e client continues wit# ot#er processing,

A, Ob=ect ;e$uest /roker )O;/* ob=ectoriented

management of communications between clients and

servers, O;/ tracks t#e location of eac# ob=ect and routes

re$uests to eac# ob=ect,

6, S:Loriented .ata ccess middleware betweenapplications and database servers, 7as t#e capabilit" to

translate generic S:L into t#e S:L specific to t#e database


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Database middlewareDatabase middleware

O./C ' Open .atabase Connectivit" most ./ vendors

support t#is

OL./ 0icrosoft en#ancement of O./C

?./C ' ?ava .atabase Connectivit" Special ?ava classest#at allow ?ava applications+applets to connect to databases

CO;/ ' Common Ob=ect ;e$uest /roker rc#itecture '

specification of ob=ectoriented middleware

.CO0 ' 0icrosofts version of CO;/ ' not as robust as

CO;/ over multiple platforms


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Client/Server securityClient/Server security

5etwork environment #as comple8 securit" issues, 5etworkssusceptible to breac#es of securit" t#roug# eavesdropping%unaut#orised connections or unaut#orised retrieval of packetsof information flowing round t#e network, Specific securit"issues include&

S"stemlevel password securit" ' user names and passwordsfor allowing access to t#e s"stem, Password managementutilities

.atabaselevel password securit" for determining accessprivileges to tablesB read+update+insert+delete privileges

Secure client+server communication via encr"ption ' butencr"ption can negativel" affect performance


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Database access from clientDatabase access from client

applicationsapplications Partitioning t#e environment to create a two% t#ree or ntier

arc#itecture means t#at decisions must be made about t#e

placement of t#e processing logic

n eac# case% storage logic )t#e database engine* is #andled

b" t#e server% and presentation logic is #andled b" t#e

client

Part a* of t#e following -ig, depicts some possible 2tier

s"stems% placing t#e processing logic on t#e client )fatclient*% on t#e server )t#in client* or partitioned across bot#

t#e server and t#e client )a distributed environment*


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Database access from clientDatabase access from client

applicationsapplications Part b* of t#e following -ig, .epicts a t"pical 3tier

arc#itecture and an ntier arc#itecture

Some processing logic could be placed on t#e client if

desired

/ut a t"pical client in a (eb enabled environment will be a

t#in client% using a browser for its presentation logic

4#e middle tiers are t"picall" coded in a portable language

suc# as ?ava

i l i di ib i


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rocessing logic distributionsrocessing logic distributions

a* 2tier

b) 3 and ntier

Processing logic could be

at client% server% or bot#

Processing logic will be at

application server or (eb

server


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!uery-by-e#ample $!%E&!uery-by-e#ample $!%E&

s t#e most widel" available directmanipulation database

$uer" language

!rap#ical approac#% bot# data retrieval and data

modification can be done b" entering ke"words% constants

and e8ample data into t#e cells of a table la"out

vailable in 0S ccess 0S ccess translates :/ to

S:L and vice versa

>seful for enduser database programming

!ood for ad #oc processing and protot"ping ' but lacks

fle8ibilit" of directl" coding in S:L


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'sing (D%C to lin) e#ternal databases'sing (D%C to lin) e#ternal databases

stored on a database serverstored on a database server

Open .atabase Connectivit" )O./C* is an P t#at provides acommon language for application programs to access and processS:L databases independent of t#e particular ;./0S t#at isaccessed

;e$uired parameters&

O./C driver needed

/ackend server name

.atabase name

>ser id and password


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'sing (D%C to lin) e#ternal databases'sing (D%C to lin) e#ternal databases

stored on a database serverstored on a database server

-ollowing -ig, S#ows generic O./C arc#itecture

Client application re$uests t#at a connection is establis#ed

wit# a data source

.river manager identifies appropriate O./C driver to use

.river selected will process t#e re$uests received from t#e

client and submit $ueries to t#e ;./0S in t#e re$uired

version of S:L

?ava .atabase Connectivit" )?./C* is similar to O./C '

built specificall" for ?ava applications

(D%C Architecture(D%C Architecture


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(D%C Architecture(D%C Architecture

Each DBMS has its own ODBC-compliant driver

Client does not need

to know anything

ao!t the DBMS

"pplication #rogram

$nter%ace &"#$' providescommon inter%ace to all

DBMSs

lec 12 client server

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