Component Design for Relational Databases - High-Performance Web Databases: Design, Development, and Deployment - page 384

management, as used in this paper, encompasses the concepts of flexibility
and robustness. It has also been argued that object-based applications by
virtue of their support for encapsulation are a natural choice for the imple-
mentation of business solutions with underlying multi-tiered architectures.
Since a component-based architecture enhances the ability of multi-tiered
architectures to deliver on its promise, it would be logical to conclude that
component-based multi-tiered architectures are here to stay.
So the prevalent application development environment can be said to
have the following features:
• Multi-tiered architecture
• Relational databases
• Object-based applications
• Component-based application architecture
APPLICATION ARCHITECTURE EXAMPLE
Now this article will take an example where a set of three tables provides
a certain functionality (e.g., hold information pertaining to interest rates in
a portfolio management system) and three discrete applications that inter-
act with these three tables. It will start with a simple two-tiered application
architecture example and note the problems in the chosen context.
Then it will move to a more object-oriented version of the same problem
and again note the problems with the approach. Finally, it will illustrate a
solution to the same problem using a data-component approach.
In Exhibit 1, Application A1 is responsible for displaying and maintaining
information in M1 (the set of tables T1, T2, and T3 constituting a sub data
model). Applications A2, A3 use the information in M1 to do their process-
ing. Note that Application A1 interacts with all the tables in M1, whereas
Applications A2, A3 interact with only T3.
The shortcomings of two-tiered applications have already been noted. In
this case, the tight coupling between the applications and the data is obvi-
ous, and consequently, flexibility is severely compromised. Also, there are
three different applications interacting with the same data and conse-
quently, complexity is increased since a change in data storage/design
would necessitate change to all the client applications.
To make this design more object-oriented, now move to Exhibit 2 which
illustrates a three-tiered object-oriented architecture. Applications A1, A2,
and A3 contain their own relational to object mapping layer (also known as
impedance matching layer). Now consider that new business rules necessi-
tate a change to M1. M1 is a sub data model corresponding to functionality
F1 (e.g., performance history of various investment options in a portfolio
management system). If the new data model involves changing the way