3-Tier Web Application Development
By Nannette Thacker
In web application development, three-tier architecture refers to separating the
application process into three specific layers. What the user sees via a web browser
is called the presentation tier and is content served from a web server. The middle
tier performs the business logic processing that occurs, for example, when a user
submits a form. The back end consists of the data tier which handles the database
processing and access to the data. We'll take a simplistic look at each of these.
The Presentation Tier or User Interface is the portion the user sees when they open
a web page in the browser. It is as simple as you reading this article all the way
to searching a catalog and purchasing a product using a shopping cart. It is what
is presented to the user on the client side within their web browser.
and Cascading Style Sheets. On some sites, you may see Java Applets and Flash. Viewing
source code on a web page, you would NOT see database queries or loops or calls
to classes or any behind-the-scenes processing.
In ASP.net and utilizing Visual Studio or Visual Web Developer
, developers can separate the user interface
from the business logic and data access layer with various tools.
ASP.net allows using MasterPages
to setup the site look and feel. As well, when
creating a WebForm which utilizes the MasterPage, you may create it and allow the
code to be placed in a separate file, known as codebehind, thus keeping your business
logic in a separate layer from the look and feel.
You may also setup the site design using Themes, Skins,
Cascading Style Sheets
Business Logic or Application Tier
The Business Logic, Functional Process Logic, Business Rules (all pertaining to
the same thing), are kept in a separate layer. In ASP.net, this is where you define
your classes and source code. This can be in the App_Code folder for your classes
and methods. Web languages typically used in ASP.net are VB and C#. You would not
functions, sub procedures, properties, etc.
Data Access Tier
In ASP.net, the Data Access layer is where you define your typed datasets and tableadapters.
It is where you define your queries or stored procedures. The business tier may
then make use of this functionality. In your classes, rather than defining ad hoc
queries, you may use a TableAdapter to access the Data Access Layer.
As an example of how this works, let's assume you are creating a web page that allows
the user to enter information which you wish to then enter into a database. You
first create a dataset and tableadapter that allows insert into the table, either
by a query or stored procedure. This is your data access layer.
You then create a class, which retrieves the information from the form, checks for
field validations and then uses the tableadapter to send the data to the database.
You create a web form, which can use a GridView control or other controls to allow
the user to input the data into the web form. In the codebehind of the web form,
you handle the submit button click event, and send the data from the form to your
class, which sends the information to the database using the tableadapter.
When utilized properly, using a multi-tier architecture improves performance and
scalability. If a web page needs an update or redesign, all of this may be handled
by altering the CSS and HTML, without affecting the business or data logic. Any
of the three tiers may be replaced or upgraded individually without affecting the
other tiers. For instance, if you change the database on the back end, it wouldn't
affect the presentation or business logic tiers, other than changing the database
This is a simple introduction to the three-tier web architecture, but I hope it
has helped you understand the layers of a multi-tier architecture.
May your dreams be in ASP.net!