Client server is a 2-tier application. In this, front end 
or client is connected to
'Data base server' through 'Data Source Name',front end is 
the monitoring level. 


Web based architecture is a 3-tier application. In this, 
browser is connected to webserver through 
TCP/IP and webserver is connected to Data base 
server,browser is the monitoring level.
In general, Black box testers are concentrating on 
monitoring level of any type of application.
 


All the client server applications are 2 tier 
architecutures.
Here in these architecutre, all the "Business Logic" is 
stored in clients and "Data" is stored in Servers. So if 
user request anything, business logic will b performed at 
client, and the data is retrived from Server(DB Server). 
 
Here the problem is, if any business logic changes, then we 
need to change the logic at each any every client. 
 
The best ex: is take a super market, i have braches in the 
city. At each branch i have clients, so business logic is 
stored in clients, but the actual data is store in servers.
If assume i want to give som discount on som items, so i 
need to change the business logic. For this i need to goto 
each branch and need to change the business logic at each 
client. This the disadvantage of Client/Server 
architecture. 
 
So 3-tier architecture came into picture:
 
Here Business Logic is stored in one Server, and all the 
clients are dumb terminals. If user requests anything the 
request first sent to server, the server will bring the 
data from DB Sever and send it to clients. This is the flow 
for 3-tier architecture. 
 
Assume for the above. Ex. if i want to give som discout, 
all my business logic is there in Server. So i need to 
change at one place, not at each client. This is the main 
advantage of 3-tier architecture.

hi 

i want to add to dharshana's answer....
the tier has nothing to do with client/server or web 
application. we can go for 2-tier in web application too 
like fetching of static html pages from server. so plz dont 
not use all client.server applications are two tier. one of 
my project is a client server application built on n-tier 
architecture...that is the business logic on server is 
spilt into many units...i wish viewers tooo add to this 
answer.

regds,
swati, swty79@rediffmail.com

In the example taken by Darshan(i.e Supermarket) for the 
client Server application how do u connect to the server?

Do an .exe or any other application is to be installed in
the client m/c to connect the server

or can we connect to the server using a browser from the
client m/c 

pls clarify

venky,

darshan is not clear, he is not specific about the 
technology used in the eg he has considered. i wish he does 
it for us to discuss more

if its web based den we could go for browser based else
we could go for .exe installation on clients we could use 
remote logins to connect to the server. do correct me if i 
am wrong. I wish someone throw highlight on thin or thick 
client concept of client server architecture.

regds,
swati
swty79@rediffmail.com