Enterprise Service Bus (ESB) - Guide to Cloud Computing for Business and Technology Managers - page 209

this step, system-level and presentation-level legacy components are
identified and separated from business-level legacy components.
In this way, candidate components are identified for wrapping.
Wrapping provides legacy functionality for new service-based solu-
tions in much shorter time than it would take to build a replacement
from scratch and recreate those dependencies. Wrapping requires
that the appropriate level of abstraction for components be deter-
mined. When it comes to wrapping and legacy componentization,
one should concentrate on identifying coarse-grained components.
Reusing a larger component saves more effort, and thus larger com-
ponents have greater value. Smaller components are more likely to
be frequently used, but their use saves less effort. This implies that
fine-grained components are less cost effective.
6. Creating service interfaces : Component wrappers result in well-defined
boundaries of functionality and data. However, the modernized
legacy system as a whole is still tightly coupled with components
hardwired to each other via program-to-program calls. The SOA
approach to large-scale system coupling requires removing from
the individual component wrappers any direct knowledge of any
other such components. This can be accomplished by breaking up
program-to-program connectivity and replacing it with service-
enabled APIs that can be used in conjunction with event-driven and
business process orchestration mechanisms.
9.6 Summary
Reliable messaging protocols are at the heart of service-oriented com-
puting architectural approaches that serve as the enabling facilitator for
addressing the requirements of loosely coupled, standard-based, and pro-
tocol-independent distributed computing. This chapter explained how
service-oriented architectures, techniques, and technologies when combined
with those of event-based programming can offer the means to achieve the
desired levels of business integration effectively, mapping IT implementa-
tions more closely to the business processes of the enterprises. Combining
Web Service standards with an ESB infrastructure can potentially deliver the
broadest connectivity between systems. An ESB supporting Web Services
with more established application integration techniques enables an enter-
prise-wide solution that combines the best of both of these worlds.