Designing N-Tier Client/Server Architecture

Introduction

Designing N-Tier client/server architecture is no less complex than developing two-tier architecture, however the N-Tier architecture, produces a far more flexible and scalable client/server environment. In two-tier architecture, the client and the server are the only layers. In this model, both the presentation layer and the middle layer are handled by the client. N-Tier architecture has a presentation layer and three separate layers - a business logic layer and a data access logic layer and a database layer. The next section discusses each of these layers in detail.

Different Layers of an N-Tier Application

In a typical N-Tier environment, the client implements the presentation logic (thin client). The business logic and data access logic are implemented on an application server(s) and the data resides on database server(s). N-tier architecture is typically thus defined by the following layers:

• Presentation Layer: This is a front-end component, which is responsible for providing portable presentation logic. Since the client is freed of application layer tasks, which eliminates the need for powerful client technology. The presentation logic layer consists of standard ASP.NET web forms, ASP pages, documents, and Windows Forms, etc. This layer works with the results/output of the business logic layer and transforms the results into something usable and readable by the end user.

• Business Logic Layer: Allows users to share and control business logic by isolating it from the other layers of the application. The business layer functions between the presentation layer and data access logic layers, sending the client's data requests to the database layer through the data access layer.

• Data Access Logic Layer: Provides access to the database by executing a set of SQL statements or stored procedures. This is where you will write generic methods to interface with your data. For example, you will write a method for creating and opening a SqlConnection object, create a SqlCommand object for executing a stored procedure, etc. As the name suggests, the data access logic layer contains no business rules or data manipulation/transformation logic. It is merely a reusable interface to the database.

• Database Layer: Made up of a RDBMS database component such as SQL Server that provides the mechanism to store and retrieve data.