Wonders of the J2EE Architecture
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by Arindam Ghosh
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Different Enterprise Application Models

Based on their functional and non-functional requirements, enterprise applications can be modeled in different ways. The enterprise application models can be divided into the following three types:

·         2-tier architecture

·         3-tier architecture

·         n-tier architecture

2-tier architecture: In the 2-tier architecture, the presentation and business logic of an application is loaded in the client PC. The server acts as a data provider. The required data for a business process is obtained from the server and processed in the client. Typical 2-tier architecture is represented in Figure shown below.

Figure 1

                       

 

 

The 2-tier architecture has the following drawbacks:

Application performance is affected due to limited resources of the PC.

Network traffic will be greater because data required for processing should be fetched from data source on server side.

Even a small change in business logic should be updated in all client PCs, which could be difficult to carry out in a large enterprise.

3-tier architecture: In the 3-tier architecture the application is divided into three different logical layers. The first tier, referred to as the presentation layer, contains the GUI part of the application. The middle tier, known as the application layer or business layer, consists of the business logic of the application. The third tier or the bottom tier, referred to as the data layer, contains data required for the application. In a typical scenario the business and data layers are available in the server side, whereas the presentation layer is in the client side. The Figure illustrates the 3-tier architecture.

Figure 2  

n-tier architecture: In the n-tier architecture the application logic is divided based on the functionality performed. The n-tier architecture can be divided into the following categories:

Client tier

The client tier or the tier-O consists of the user interface. It deals with the different type of clients interacting with the application. The user may be a browser client accessing the server-side application through a firewall or a desktop Java client accessing it from within a firewall.

Middle tier

The middle tier consists of the following components.

Presentation logic: It deals with dynamic content to the clients, user requests, and responses.

Business logic: It deals with business rules and business processes of an application.

Infrastructure services: It provides additional functionalities required by the application components such as messaging and transaction.

Data tier

The data tier consists of the data layer which provides data for the application.


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