Information Technology Reference
In-Depth Information
11.7 Legacy Systems
As well as their use in inter-organizational federation, it should be noted
that these ideas can also be used in the planning and execution of legacy
integration. Linking legacy services to a more modern infrastructure involves
management decisions about what services need to be retained and which are
obsolete and can be phased out [54]. The resulting decisions can be captured
by specifying what role the legacy system is expected to play and how this
relates to other roles within the organization.
The actual integration involves establishing a shared ontology and process
model, which may have to be reverse engineered from the existing usage of the
legacy components. Based on this, the nature and location of any necessary
converters are determined, and an engineering plan for their realization and
commissioning written. Finally, a plan for the eventual transition away from
the legacy components and for their decommissioning will be needed.
11.8 Interoperability or Integration?
How is the decision whether to federate or to integrate related systems to
be made? It is a dicult trade-off involving a variety of costs and depends on
assumptions about the way the organizations will evolve.
Firstly, stronger integration allows more informed management, which re-
sults in more ecient and more reliable operation. There will be more com-
plete sharing of information models (although legacy barriers will persist) and
so more consistency and better planning follow.
On the other hand, this close coupling means that the different systems
depend on each other, so that withdrawal of any party damages the remain-
der of the organization. If there is significant autonomy of the components,
changes of their objectives may result in the necessary level of cooperation
and sharing being lost. However, the strongest reason for concentrating on
interworking is that, as organizations evolve, their groupings change, and in-
tegration measures have to be repeatedly reworked, placing an intolerable
burden on an organization with many business links, while a good implemen-
tation of a standards-based interworking strategy will support an evolving set
of partners with lower maintenance and thus much lower total cost. Integra-
tion creates longer range ordering, which physics tells us is a sure sign that a
fluid system is about to freeze solid. In a nutshell, federation reduces threats
from changes of the partners' objectives, and integration allows more ratio-
nalization, but limits the partners' freedom of action and the system's future
flexibility.
