Page 35 - Accounting Information Systems

6 PART I Overview of Accounting Information Systems

An Example of an Artificial System
An automobile is an example of an artificial system that is familiar to most of us and that satisfies the def-
inition of a system provided previously. To simplify matters, let’s assume that the automobile system
serves only one purpose: providing conveyance. To do so requires the harmonious interaction of hun-
dreds or even thousands of subsystems. For simplicity, Figure 1-2 depicts only a few of these.
In the figure, two points are illustrated of particular importance to the study of information systems:
system decomposition and subsystem interdependency.

SYSTEM DECOMPOSITION. Decomposition is the process of dividing the system into smaller sub-
system parts. This is a convenient way of representing, viewing, and understanding the relationships
among subsystems. By decomposing a system, we can present the overall system as a hierarchy and view
the relationships between subordinate and higher-level subsystems. Each subordinate subsystem performs
one or more specific functions to help achieve the overall objective of the higher-level system. Figure 1-2
shows an automobile decomposed into four primary subsystems: the fuel subsystem, the propulsion sub-
system, the electrical subsystem, and the braking subsystem. Each contributes in a unique way to the sys-
tem’s objective, conveyance. These second-level subsystems are decomposed further into two or more
subordinate subsystems at a third level. Each third-level subsystem performs a task in direct support of its
second-level system.

SUBSYSTEM INTERDEPENDENCY. A system’s ability to achieve its goal depends on the effective
functioning and harmonious interaction of its subsystems. If a vital subsystem fails or becomes defective
and can no longer meet its specific objective, the overall system will fail to meet its objective. For exam-
ple, if the fuel pump (a vital subsystem of the fuel system) fails, then the fuel system fails. With the fail-
ure of the fuel system (a vital subsystem of the automobile), the entire system fails. On the other hand,
when a nonvital subsystem fails, the primary objective of the overall system can still be met. For instance,
if the radio (a subsystem of the electrical system) fails, the automobile can still convey passengers.
Designers of all types of systems need to recognize the consequences of subsystem failure and provide
the appropriate level of control. For example, a systems designer may provide control by designing a

FI GU RE
1-2 PRIMARY SUBSYSTEM OF AN AUTOMOBILE

Automobile

Fuel Propulsion Electrical Brake
System System System System

Brake
Fuel Tank Engine Lights
Pedal
Trans- Master
Fuel Pump Ignition
mission Cylinder

Rear Brake
Fuel Injector Radio
Axle Lines

Wheels Battery Disk