Software Engineering-Computer Based Systems

The word system is possibly the most overused and abused term in the technical lexicon. We speak of political systems and educational systems, of avionics systems and manufacturing systems, of banking systems and subway systems. The word tells us little. We use the adjective describing system to understand the context in which the word is used. Webster's Dictionary defines system in the following way:

1. a set or arrangement of things so related as to form a unity or organic whole; 2. a set of facts, principles, rules, etc., classified and arranged in an orderly form so as to show a logical plan linking the various parts; 3. a method or plan of classification or arrangement; 4. an established way of doing something; method; procedure . . .

Five additional definitions are provided in the dictionary, yet no precise synonym is suggested. System is a special word.

Borrowing from Webster's definition, we define a computer-based system as
A set or arrangement of elements that are organized to accomplish some predefined goal by processing information.

The goal may be to support some business function or to develop a product that can be sold to generate business revenue. To accomplish the goal, a computer-based system makes use of a variety of system elements:

Computer programs, data structures, and related documentation that serve to effect the logical method, procedure, or control that is required.

Hardware. Electronic devices that provide computing capability, the interconnectivity devices (e.g., network switches, telecommunications devices) that enable the flow of data, and electromechanical devices (e.g., sensors, motors, pumps) that provide external world function.

People. Users and operators of hardware and software.

Database. A large, organized collection of information that is accessed via software.
Documentation. Descriptive information (e.g., hardcopy manuals, on-line help files, Web sites) that portrays the use and/or operation of the system.

Procedures. The steps that define the specific use of each system element or the procedural context in which the system resides.
The elements combine in a variety of ways to transform information. For example, a marketing department transforms raw sales data into a profile of the typical purchaser of a product; a robot transforms a command file containing specific instructions into a set of control signals that cause some specific physical action. Creating an information system to assist the marketing department and control software to support the robot both require system engineering.

One complicating characteristic of computer-based systems is that the elements constituting one system may also represent one macro element of a still larger system. The macro element is a computer-based system that is one part of a larger computer-based system. As an example, we consider a "factory automation system" that is essentially a hierarchy of systems. At the lowest level of the hierarchy we have a numerical control machine, robots, and data entry devices. Each is a computerbased system in its own right. The elements of the numerical control machine include electronic and electromechanical hardware (e.g., processor and memory, motors, sensors), software (for communications, machine control, interpolation), people (the machine operator), a database (the stored NC program), documentation, and procedures.A similar decomposition could be applied to the robot and data entry device. Each is a computer-based system. 
At the next level in the hierarchy, a manufacturing cell is defined. The manufacturing cell is a computer-based system that may have elements of its own (e.g., computers, mechanical fixtures) and also integrates the macro elements that we have called numerical control machine, robot, and data entry device.

To summarize, the manufacturing cell and its macro elements each are composed of system elements with the generic labels: software, hardware, people, database, procedures, and documentation. In some cases, macro elements may share a generic element. For example, the robot and the NC machine both might be managed by a single operator (the people element). In other cases, generic elements are exclusive to one system.

The role of the system engineer is to define the elements for a specific computerbased
system in the context of the overall hierarchy of systems (macro elements). In
the sections that follow, we examine the tasks that constitute computer system engineering.
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