Information Technology Reference
In-Depth Information
Legacy applications are critical assets of any modern enterprise as they
provide access to mission-critical business information and functional-
ity and thus control the majority of an organization's business processes.
Legacy applications could implement core business tasks such as taking and
processing orders, initiating production and delivery, generating invoices,
and crediting payments, distribution, inventory management, and related
revenue-generating, cost-saving, and accounting tasks. Being able to leverage
this value in new ESB-based solutions would provide an extremely attractive
return on existing investments. Therefore, a best-of-breed ESB characteristic
is to offer connectivity for legacy applications.
It is not possible to properly integrate legacy systems into Web Service
solutions without extensive, intrusive modifications to these systems.
Modifications are needed to reshape legacy systems to provide a natural fit
with the Web Service architectural requirements and carefully retrofit busi-
ness logic so that it can be used with new applications. Therefore, legacy
applications need to be reengineered in order to reuse the core business pro-
cesses entrenched in legacy applications. The legacy system reengineering
process involves the disciplined evolution of an existing legacy system to a
new improved environment by reusing as much of it (implementation, design,
specification, requirements) as possible and by adding new capabilities.
Through reengineering, business processes become more modular and gran-
ular exposing submodules that can be reused and are represented as services.
The primary focus of legacy reengineering and transformation is enter-
prises, business processes, the EAI, and how a legacy system can contribute
to implementing the architecture without propagating the weaknesses of
past designs and development methods. In its most fundamental form, the
process of re-engineering involves three basic phases.
1. Understanding of an existing application, resulting in one or more
logical descriptions of the application
2. Restructuring or transformation of those logical descriptions into
new, improved logical descriptions
3. Development of the new application based on these improved logi-
cal descriptions
The re-engineering and transformation steps in the following
have been considerably simplified. The purpose of these steps
is to facilitate the process of legacy application modernization
by modularizing legacy processes and business logic separately
from presentation logic and data management activities, and
representing them as components. These components can then be used
to create interfaces for new services, thereby service enabling legacy
applications.
 
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