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  Summary

  A framework is a set of common and prefabricated software building blocks that programmers can use, extend or customize for specific computing solutions. With frameworks developers do not have to start from scratch each time they write an application. Frameworks are built from collection of objects so both the design and code of the framework may be reused.

 



App Building Approaches   
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The J2EE platform is designed for multi-tier applications, and offers a lot of flexibility in choosing how to distribute application functionality across the tiers. In a Web-enabled application some tiers are always present: the client tier provided by the browser, the Web tier provided by the server and the enterprise information system or database tier which holds persistent application data. The first choice to make is whether the Web tier accesses the enterprise information system resources directly, or goes through an EJB tier. The decision depends on the functionality, complexity, and scalability requirements of the application. Since such requirements can change as the application evolves, one goal for the design is to make it amenable to migration to an EJB-centric approach.


Web-Centric Approach

In a Web-centric design, the Web tier communicates directly with the enterprise information system resources that hold application data. In this approach, the Web tier is responsible for almost all of the application functionality. It must take care of dynamic content generation and presentation and handling of user requests. It must implement core application functionality such as order processing and enforce business rules defined by the application. Finally, the components running in the Web tier must also manage transactions and connection pooling for data access. Because it must handle so many functions, Web-centric application software has a tendency to become monolithic. As a result, unless special efforts are taken, it does not scale well with increasing software complexity.


EJB Centric Approach

In an EJB-centric design, enterprise beans running on EJB servers encapsulate the enterprise information system resources and the core application logic. The Web tier communicates with the EJB tier instead of directly accessing the enterprise information system resources. This approach moves most of the core application functionality to the EJB tier, using the Web tier only as a front end for receiving client Web requests and for presenting HTML responses to the client.

The principal advantage of this approach is that enterprise beans have access to a broad set of enterprise-level services. Because of these services, managing transaction and security aspects of the application is easier. The EJB container provides a highly structured environment for the components that allows a developer to focus entirely on the application domain issues, while the EJB container takes care of system-level details. These standardized container-provided services also translate into better software reliability. The EJB architecture supports a programming discipline that promotes encapsulation and componentization, resulting in software that stays manageable, as applications grow more complex.


Our Approach

The Web-centric approach is better for getting the application off to a quick start, while EJB-centric approach becomes more desirable when building a large-scale application where code and performance scalability are prime factors. While the Web-centric approach may be more prevalent, with many applications implemented using it, it has limitations when building large scale, complex applications. Our approach is an approach that benefits from the strengths of both approaches. So we are looking for decisions that may start as web-centric application and later on easy to migrate to EJB-centric ones. So if the Web-centric approach is used at the beginning of the development, it should have a strong logical separation between the presentation and the business parts.



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