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.
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, and Cascading Style Sheets.
Business Logic or Application Tier
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 connection.
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!