Enterprise Service Bus (ESB) - Guide to Cloud Computing for Business and Technology Managers - page 195

and trading partner management functionality, packaged adapters, and
user-driven applications through front-end capabilities such as Java Server
Pages (JSPs).
In an ESB, the functionality of an integration broker, such as messaging
and connectivity, application adapters, a data transformation engine, and
routing of messages based on business rules, is spread out across a highly
distributed architecture that allows selective deployment and independent
scalability of each of those pieces. This is an important difference from the
classic integration broker model where these capabilities are localized to
a central monolithic server. In many situations, it is essential that newly
developed ESB solutions be bridged to existing integration broker installa-
tions. In this scenario, the integration broker installation now becomes the
asset, which the ESB utilizes to support new application development in
future.
9.2.2 Application Servers
Another critical middleware infrastructure used in connection with ESBs
is application servers. Application servers offer an integrated development
environment for developing and deploying distributed Web- and non-web-
based applications and services. Application servers typically provide Web
connectivity for extending existing solutions and bring transaction process-
ing mechanisms to the Web. An application server is a natural point for
application integration as it provides a platform for development, deploy-
ment, and management of web-based, transactional, secure, distributed, and
scalable enterprise applications. The application server middleware enables
the functions of handling business processes and transactions as well as
extending back-end business data and applications to the Web to which
it exposes them through a single interface, typically a Web browser. This
makes application servers ideal for portal-based ESB development. Unlike
integration brokers, application servers do not integrate back-end systems
directly but rather act as an integrated development and support frame-
work for integrating business processes between enterprises. An application
server expects the integration broker to function as a service provider pro-
viding data access, transformations, and content-based routing.
The adapter/component wrapper modules are responsible for providing
a layer of abstraction between the application server and the component ES.
This layer allows for ES component communications, as if the component ES
were executed within the application server environment itself. Execution
in this type of architecture occurs among component wrappers within the
application server. The component wrappers in this facilitate point integra-
tion of component systems by wrapping legacy systems and applications
and other back-end resources such as databases, ERP, CRM, and SRM, so that
they can express data and messages in the standard internal format expected
by the application server. The application server is oblivious to the fact that