Distributed Systems - Guide to Cloud Computing for Business and Technology Managers - page 71

respective adapters for this broker that uses the singular format and
protocol of this central broker. Any future systems have to devise only
one adapter to integrate with the central broker to start communicating
transparently with all other systems. The exchange of data between the
various systems interconnected by EAI is governed by the business
rules determined by the user; and the message broker routes the mes-
sages according to these rules. However, the data in the messages are
translated en route into whatever format is required by the concerned
application.
• Simplified systems management : The n-tier architecture is useful in
reducing the effort of systems management especially of the soft-
ware on client machines, particularly for large enterprises that may
have tens of thousands of client machines or even for enterprises that
have multilocated and decentralized IT/IS operations. For instance,
for conventional client/server systems, the plan for deploying a new
version of any application would immediately run into a difficulty of
choosing between
• Changing the entire installed base of clients in a single massive
effort during which the normal operations come to a complete
standstill
• Undergoing a long and expensive but more regulated phase-in
of the new software, during which IT/IS is required to support
multiple and mutually incompatible versions of the server and
client codes, and above all, the new application is available to
only a part of the target user base
N-tier architecture by reason of its software-on-demand paradigm reduces
the need for physical updates of the client machines considerably; in many of
these cases, the updates can be distributed through HTTP and a Web browser
or through separately available automatic application distribution systems.
But in the case of applications with zero footprint clients like SAP CRM, this
need is completely eliminated. Moreover, as the majority of the code resides
in the business logic, middleware, and data layers that are typically deployed
on centralized, back-end servers supported by professional staff, the updates
and enhancements to these layers are relatively painless.
3.1.1.2 Limits of the N-Tier Architecture
While n-tier architectures deliver all the advantages associated with distrib-
uted systems, they also have a downside. N-tier systems are workable only
because of a network-based data bus for communications between the vari-
ous tiers.