J2EE for Enterprise Integration - Guide to Cloud Computing for Business and Technology Managers - page 138

components, higher-quality test-driven development via pretested
components, and easier maintenance via cost-effective upgrades to
individual components.
• J2EE offers support for hardware and Operating systems (OS) inde-
pendence by enabling system services to be accessed via Java and
J2EE rather than directly via APIs specific to the underlying systems.
• J2EE offers a wide range of APIs to access and integrate with third-
party products in a consistent manner, including databases, mail
systems, and messaging platforms.
• J2EE offers clear-cut segregation between system development,
deployment, and execution, thus enabling independent develop-
ment, integration, and upgradation of components.
• J2EE offers specialized components that are optimized for specific
types of roles in an enterprise application like Entity Beans for han-
dling persistent data and Session Beans for handling processing.
All the aforementioned features make possible rapid development of com-
plex, distributed applications by enabling developers to focus on develop-
ing business logic, implementing the system without being impacted by
prior knowledge of the target execution environment(s), and creating sys-
tems that can be ported more easily between different hardware platforms
and Operating systems (OS).
6.2.1 Reference Architecture
The objective of the flexibility and reusability can be achieved primarily
at two levels: application architecture level and the application component
design level. The reference architecture is the vision of the application archi-
tecture that integrates common elements into a component structure model-
ing the current business and also positioning it to meet the challenges of the
future. From a technical point of view, the architecture positions the devel-
opment organization to automatically meet the benchmark requirements on
time to market, flexibility, and performance.
A set of key elements drive the definition of the reference architecture that
is comprised of three layers, namely, business objects, process-oriented or
service-based objects, and user interface layer.
The defining elements of enterprise applications are as follows:
• Business entities are the foci of the enterprise applications. These
range from top-level entities such as a customer or a supplier down
to bottom-level entities such as purchase orders, sales orders, or even
individual level line items of these orders. Entities participate in the
business processes, have attributes or properties, have methods for
responding to requests for information, and have different sets of