Answer Posted / manju

What is Difference Between Two-Tier and Three-Tier Architecture?

In my previous post I have outlined points to be considered
while testing Web based applications. In today’s software
testing class we are discussing about the Two-Tier and
Three-Tier architecture.

All projects are broadly divided into two types of
applications 2 tier and 3 tier architecture. Basically high
level we can say that 2-tier architecture is Client server
application and 3-tier architecture is Web based
application. Below I am concentrating on the difference
between Two-Tier and Three-Tier Architecture, what all
advantages, disadvantages and practical examples.
Two-Tier Architecture:

The two-tier is based on Client Server architecture. The
two-tier architecture is like client server application. The
direct communication takes place between client and server.
There is no intermediate between client and server. Because
of tight coupling a 2 tiered application will run faster.
Two-Tier Architecture

Two-Tier Architecture

The above figure shows the architecture of two-tier. Here
the direct communication between client and server, there is
no intermediate between client and server.

Let’s take a look of real life example of Railway
Reservation two-tier architecture:

Let’s consider that first Person is making Railway
Reservation for Mumbai to Delhi by Mumbai Express at Counter
No. 1 and at same time second Person is also try to make
Railway reservation of Mumbai to Delhi from Counter No. 2

If staff from Counter No. 1 is searching for availability
into system & at the same staff from Counter No. 2 is also
looking for availability of ticket for same day then in this
case there is might be good change of confusion and chaos
occurs. There might be chance of lock the Railway
reservation that reserves the first.

But reservations can be making anywhere from the India, then
how it is handled?

So here if there is difference of micro seconds for making
reservation by staff from Counter No. 1 & 2 then second
request is added into queue. So in this case the Staff is
entering data to Client Application and reservation request
is sent to the database. The database sends back the
information/data to the client.

In this application the Staff user is an end user who is
using Railway reservation application software. He gives
inputs to the application software and it sends requests to
Server. So here both Database and Server are incorporated
with each other, so this technology is called as
“Client-Server Technology“.

The Two-tier architecture is divided into two parts:

1) Client Application (Client Tier)
2) Database (Data Tier)

On client application side the code is written for saving
the data in the SQL server database. Client sends the
request to server and it process the request & send back
with data. The main problem of two tier architecture is the
server cannot respond multiple request same time, as a
result it cause a data integrity issue.

Advantages:

Easy to maintain and modification is bit easy
Communication is faster

Disadvantages:

In two tier architecture application performance will be
degrade upon increasing the users.
Cost-ineffective

Three-Tier Architecture:

Three-tier architecture typically comprise a presentation
tier, a business or data access tier, and a data tier. Three
layers in the three tier architecture are as follows:

1) Client layer
2) Business layer
3) Data layer

1) Client layer:

It is also called as Presentation layer which contains UI
part of our application. This layer is used for the design
purpose where data is presented to the user or input is
taken from the user. For example designing registration form
which contains text box, label, button etc.

2) Business layer:

In this layer all business logic written like validation of
data, calculations, data insertion etc. This acts as a
interface between Client layer and Data Access Layer. This
layer is also called the intermediary layer helps to make
communication faster between client and data layer.

3) Data layer:

In this layer actual database is comes in the picture. Data
Access Layer contains methods to connect with database and
to perform insert, update, delete, get data from database
based on our input data.
Three-tier Architecture

Three-tier Architecture

Advantages

High performance, lightweight persistent objects
Scalability – Each tier can scale horizontally
Performance – Because the Presentation tier can cache
requests, network utilization is minimized, and the load is
reduced on the Application and Data tiers.
High degree of flexibility in deployment platform and
configuration
Better Re-use
Improve Data Integrity
Improved Security – Client is not direct access to database.
Easy to maintain and modification is bit easy, won’t
affect other modules
In three tier architecture application performance is good.

Disadvantages

Increase Complexity/Effort

This is the common Question asked in the Interview. Hope
this article helped you understanding Two-Tier and
Three-Tier Architecture with example.
Thanks and Happy Testing!!!

I think this will have an idea of two-tier and three-tier
architecture. To get software testing articles in your inbox
click here to Subscribe with your email address link. Also I
would like all of you to please join this discussion and add
more valuable points to it. Thanks.

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