.NET Assemblies - I

This article is going to be based on three parts.

1. In the first part we will be discussing the 3-tier architecture.

2. In part-II of this article we will see what the .NET assemblies are and

3. In the last part we will be practically implementing a simple .NET assembly.

Part-I :: The Three-Tier Architecture

A 3-tier architecture defines the division of a web based application into three layers. When we say 3-tier architecture, we are actually meaning the number of nodes (or computers) that are involved within the communication. Let's first of all see what do I mean when I say a 3-tier architecture or a n-tier architecture.

For example, consider a simple scenario in which we have a client/server architecture. A user simply connects with the server and communication starts. The server fulfills all the requirements of the client as all of the contents have been placed on the server. This type of architecture is called as a client/server architecture or it can also be said as a two-tier architecture.

In a two-tier architecture the server contains all the contents that would be requested from the client, the contents can include web pages, the server-side technology implemented and the data-store. If we separate the contents of the server-side technology from the web pages and place them on a separate machine then this architecture would become a three-tier architecture. Similarly if we keep on increasing the number of machines in between our client/server communication then we would be implementing the n-tier architecture for our communication.

Why do we need the three-tier architecture?

The three-tier architecture was introduced for better management of code and contents and to improve the performance of the web based applications. Within the three-tier architecture we divide our application into a set of three layers.

1. Presentation

2. Business Logic

3. Database

• The first layer Presentation contains the interface code, that is going to be displayed to the user. This code could contain any technology that can be used on the client side like HTML, JavaScript or VBScript etc.

• The second layer Business Logic contains all the code of the server-side technology. This layer mainly contains the code that is used for accessing the database and to query, manipulate, pass data to user interface and handle any input from the UI as well.

• The third and last layer Data represents the data store like MS Access, SQL Server, an XML file, an Excel file or even a text file containing data.

The following diagram shows the layers we have just described.

(Figure Displaying the layers of the three-tier architecture)

One of the main benefits of the three-tier architecture is easy management of the contents of the web application. Consider a scenario in which you require to change the presentation of the web pages because you have recently designed a new look for your website. In the case of two-tier architecture you would require to change the web pages that would be containing both the contents for the presentation as well as the business logic, this would mean an headache for you to keep the code for business logic as it is and change the code for the presentation layer. In case of a three-tier architecture the code of the business logic would be residing on the middle layer, there for you would be requiring only to make a change on the presentation layer containing the code for your web page designs.Similarly if you require to change the database system for example, from Access to Sql Server, then you would require only to change the database on the data server without having to make any changes within the code of your business logics.

The three-tier application design also enables for better performing web applications, since the whole load of users is not placed upon a single server. As we can see in the figure displaying the design of a three-tier architectured web application, it can be seen that placing the business logic and the database on the different machines reduces the load upon a single server. Similarly we can implement any number of servers we like on the backend of the application and such an architecture would be known as n-tier architecture.