chap 2.client server computing (ch1,2)

7/27/2019 Chap 2.Client Server Computing (Ch1,2)

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Client Server Computing

Ch 1,2 of syllabus


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The Good Old Days .

In Olden days Mainframes were

used .


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What are Mainframes ?A mainframe is simply a very large computer

The name comes from the way the machine isbuild up.

All units (processing, communication etc.)were hung into a frame. Thus the

maincomputer is build into a frame, therefore:Mainframe


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Mark I mainframe

(1950's)


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Mainframes are used : used mainly by large organizations for critical

applications, typically bulk data processing such as

census,industry and consumer statistics, ERP, andfinancial transaction processing.

To run commercial applications of Fortune 1000businesses and other large-scale computing

purposes.

Banking and insurance businesses


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A computer Vs a MainframeA mainframe has 1 to 16 CPU's (modern

machines more)

Memory ranges from 128 Mb over 8 Gigabyteon line RAM

Its processing power ranges from 80 over 550

Mips


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It has often different cabinets for Storage I/O RAM

Separate processes (program) for task management program management job management serialization catalogs inter address space

communication


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Mainframes Choose a vendor .

Analyst supervise it and set proper

Operating System . Data Communication Specialist .

Storage Specialists :hook up frames disk &

tape drives Maintenance & System Managementbuild

in every component .


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After Revolution .. World ofClient/Servers and Open

systems .

Choice for each and every component .

Mix and Match Components .


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Chapter 2

Welcome to C/S ComputingReal Client /Server Vision

Client /Server Computing provides anopen and flexible environment .

Mix and Match is the rule .

Client applications are on PCs/Desktops. Servers know how to communicate with

PC client .


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Internet and Intranet The WWW is redefining Client /Server

Computing .

Corporate LANS and WANS are becoming partof Internet .

Extranet is used .

Refers to an intranet that is partially accessible toauthorized outsiders .

Intranet resides behind a firewall


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It is accessible only to people who are membersof the same company or organization

An Extranet provides various levels ofaccessibility to outsiders.

Virtual Private Networks (VPNs) is technology totunnel through the public network.
http://searchsecurity.techtarget.com/sDefinition/0,,sid14_gci213324,00.htmlhttp://searchsecurity.techtarget.com/sDefinition/0,,sid14_gci213324,00.html


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Enterprise Resource Planning systems (ERPs)integrate all data and processes of an organization

into a unified system. A typical ERP system will use multiple components

of computer software and hardware to achieve theintegration.

A key ingredient of most ERP systems is the use ofa unified database to store data for the varioussystem modules


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ERP Client/Server Craze ERP applications are provided by

companies like SAP,PeopelSoft,Oracle etc.

They provide packaged Client/Seversolution for back office enterprisefunctions .

Give solution for Accounting ,Payroll,human Resources .


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Provide Single user Interface .

All pieces from same vendor to get

integration .


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ERP sys are not really turn key

It gives 80% solution .

ERP requires re-engineering of company'sprocess and culture .

Change operations to match ERP package .

ERP must be integrated with rest ofenvironment .


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Built Infrastructure that ties with new ERPpackage .(Database,Web-serversLAn based app.)

ERP dont give competitive advantage .


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What is Client/Server ?

Clients and Servers are two separatelogical entities that work together over a

n/w to accomplish a task .


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Characteristics for Client /ServerSystems .

Service

A client is defined as a requester / consumer ofservices and a server is defined as the providerof services .

Shared Resources

AServer provides service/s to many clients at atime .

Regulate access to shared resources


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Asymmetrical protocols

Many-to-one relationship between Clientsand servers.

Client gives request .

The server responds to data (andapplication) requests from the client .


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Transparency of Location

A single machine can be both a client

and a server depending on the softwareconfiguration .

Server is a process that can reside on

same m/c as that of client . It can reside on different m/c on

network.


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Mix and Match

Ideal Client/Server s/w is independentof h/w & OS.

(e.g. Internet )Message Based Exchange.

Interaction through message Passing Mechanism.


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Scalability

C/S System can be scaled in two

ways :Horizontal:Adding /Removing clientswithout much impact on performance .

Vertical :Migrating to larger /fasterserver .


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Real C/S?File servers

Store the files that are created by the networkusers.

They also store applications such as word

processing programs, spreadsheets etc. Users can access parts of a file server's hard disk

which will appear as an extra drive on their own

computer. Applications can either be run from the fileserver,

or they can be downloaded to the user'sworkstation


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Used for sharing files on n/w . They are required for creating shares storage

for documents, images , Engg.drawing .


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A computer in a LAN dedicated to database

storage and retrieval. The database server is a key component in a

client/server environment. It holds the databasemanagement system (DBMS) and the databases.

Upon requests from the client machines, itsearches the database for selected records andpasses them back over the network.

Database Servers .


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Client passes SQL requests as messages tothe database server .

Code processes SQL request & the datareside on the same m/c.

Plays key role for important queries &flexible reports .


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Groupware Servers

A groupware server is software designed toenable users to collaborate, regardless of

location, via the Internet or a corporateintranet and to work together in a virtualatmosphere .

These Client/Server systems place people indirect contact with other people .

Lotus Notes, Microsoft Exchange .


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In most cases ,applications are developedusing scripting language & form-based i/fs .

Many Groupware uses E-mail as theirstandard messing middleware .

Internet is becoming middleware platform

for groupware .


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Transaction Server Client invokes remote procedures that reside in

server .

These remote procedures on server executea group of SQL Statements .

N/W exchange consist of single request/reply .

SQL statements either succeed or fail . These grouped SQL statements are called

transactions .


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Client component usually includes GUI

Server consists of SQL Transactions against a

data base . These are called Online Transaction Processing .


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Object Application Servers

Client/Server Application is written as a set ofcommunication objects .

Client objects communicate with server objectusing Object Request Broker. (ORB)

Client invokes a method on a remote object .

The ORB locates an instance of that objectserver class .


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There are currently two prominentdistributed object technologies:

Common Object Request BrokerArchitecture (CORBA)

COM/DCOM
http://www.sei.cmu.edu/str/descriptions/corba.htmlhttp://www.sei.cmu.edu/str/descriptions/corba.htmlhttp://www.sei.cmu.edu/str/descriptions/corba.htmlhttp://www.sei.cmu.edu/str/descriptions/corba.html


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Web Application Server

Aweb server serves web pages to clientsacross the Internet or an Intranet.

The web server hosts the pages, scripts,programs, and multimedia files and servesthem using HTTP, a protocol designed to

send files to web browsers and otherprotocols.

Web Server returns documents

when client asks them by name .


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The most common web server is

Apache (available for all major operatingsystems) though IIS (InternetInformation Server - available on theWindows Platform) is a fast growing

web server.


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FAT server /FAT Client

C/S applications can be differentiated by how theapplication is split between client & server.

FAT Client:

A Client that performs the bulk of the dataprocessing operations. The data itself is stored onthe Server .

FAT Client places more functions on Client . Client performs the bulk of any data processing

operations itself.

Provide flexibility & opportunity for creating Front

end tools


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FAT Server

A server in a client/server environment that

performs most or all of the applicationprocessing with little or none performed in theclient .

FAT server application are easier to manage&deploy on n/w bcos most of the code runs onserver .


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Fat Client Examples

File Server

Fat Server Examples

Groupware, Transaction ,Web server


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Different Architectures basically splitClient/Server applications into different

functional units that can be assigned to clientsor servers .


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2 Tier Architecture

A two-way interaction in a client/serverenvironment, in which the user interface is

stored in the client and the data are stored inthe server .

In 2 tier C/S System application logic is buried

either inside the user i/f on client or withindatabase on server.


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Application logic & business logic reside

on Client m/c . Database runs on the server computer.


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The method that's most commonly used is theStructured Query Language (SQL).

The SQL statement is sent to the databaseserver, which performs the work locally onthat physical computer and returns only therelevant information (the answer) to the clientPC .

Only the database services are separated fromthe application in a two-tier design.

The presentation and business logic layersremain very intertwined, and both continue tohave intimate knowledge of the database.


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Three Tier Architecture .

A three-tier architecture is any systemwhich enforces a general separation

between the following three parts: Client Tieror user interface

Middle Tieror business logic

Data Storage Tier


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Tier 1: the client contains the presentation logic,including simple control and user input validation. Thisapplication is also known as a thin client.

Tier 2: the middle tier is also known as the applicationserver, which provides the business processes logic

and the data access. Tier 3: the data server provides the business data. Advantages of a three-tier architecture:

It is easier to modify or replace any tier without

affecting the other tiers. Separating the application and database

functionality means better load balancing. Adequate security policies can be enforced within the

server tiers without hindering the clients


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Applied to web applications and distributedprogramming, the three logical tiers usually

correspond to the physical separation betweenthree types of devices or hosts:

Browser or GUI Application

Web Server or Application Server Database Server (often an RDBMS or

Relational Database)


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In a three-tier client/server application,the presentation layer usually does nothave intimate knowledge of thedatabase.

Instead, the presentation layercommunicates with its applicationserver using a predifined messagestrategy.


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Your browser knows absolutely nothing aboutthe structure of the database at Amazon.com,

for example but you are nevertheless able tointeract with that database when you order abook.

This is the result of well-defined Internetprotocols that allow the client (the browser) totalk to an application server (a Web site).


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Architecture

Pros Cons

One tier SimpleVery highperformance

Self-contained

No networking --can'taccess remote services

Twotiers

Clean, modulardesignLess network traffic

SecurealgorithmsCan separate UI from

business logic

Must design/implement protocolMust

design/implementreliable data

storage


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N-tier Architecture

N-Tier architecture refers to the architecture of anapplication that has at least 3 "logical" layers -- or

parts -- that are separate. Each layer interacts withonly the layer directly below, and has specificfunction that it is responsible for.

Because each layer can be located on physically

different servers with only minor code changes,hence they scale out and handle more server load.


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A good example of a n-tier distributedapplication is a stock-trading system.

In this environment, multiple data feeds(stock quotes, news, trading orders) arrivefrom different sources, multiple databases

(accounts, logs, historical data) areaccessed, and multiple clients run specializedapplications.

It makes sense to weave together thedisparate patches in this quilt with the threadof a common distributed object architecture,like CORBA or EJB.


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Benefits of using middle layer as acomponent based application

Big applications can be developed as smallones .

Application can reuse components

Clients can access data & functions easily &safely .


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When should 3 tier be used ?

Many applications services or classesmorethan 50

Applications programmed in differentlanguages or written by differentorganizations .

Two /more heterogeneous data sourcessuch as data base & a file system.

chap 2.client server computing (ch1,2)

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