Distributed Systems - Guide to Cloud Computing for Business and Technology Managers - page 69

automated. Consequently, the business logic tended to split between the cli-
ent and the server; typically, the rules for displaying data became embedded
inside the user interface, and the rules for integrating several different data
sources became stored procedures inside the database. Whereas this division
of logic made it difficult to reuse the user interface code with a different data
source, it also made it equally difficult to use the logic stored in the database
with a different front-end user interface (like ATM and mobile) without being
required to redevelop the logic implemented in the earlier interface. Thus, a
customer service system developed for a particular client system (like a 3270
terminal, a PC, or a workstation) would have great difficulty in providing
telephony and Internet interfaces with the same business functionality.
The client/server architecture failed to recognize the importance of man-
aging the business rules applicable to an enterprise independent of both the
user interface and the storage and management of enterprise data. The three-
tiered application architecture of the 1990s resolved this problem by subdi-
viding the application into three distinct layers:
1. Data management, which stores and manages data independent of
how they are processed and displayed by the other layers
2. Business logic, which implements the business logic to process data
independent of how they are stored or displayed by the other two
layers
3. Presentation, which formats and displays the data independent of the
way they are interpreted/processed and stored by the other two layers
With the advent of the Internet in the past few years, the three tiers were split
even further to accommodate the heterogeneity in terms of the user interfaces,
processing systems, or databases existing in various parts of an enterprise.
The power of the n-tier architecture derives from the fact that
instead of treating components as integral parts of applications,
components are treated as stand-alone entities, which can pro-
vide services for applications. Applications exist only as cooper-
ating constellation of components, and each component in turn can
simultaneously be part of many different applications.
3.1.1.1 N-Tier Architecture Advantage
The n-tier architecture has many advantages over the more traditional client/
server architecture:
• Agile software : The n-tier architecture is useful in creating more flex-
ible and easily modifiable software. By treating software compo-
nents as stand-alone data providers, middleware service providers,