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CHAPTER 10 SYSTEM ENGINEERING 247

Software. 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 inter-
connectivity devices (e.g., network switches, telecommunications devices)
Don’t be lured into that enable the flow of data, and electromechanical devices (e.g., sensors,
taking a “software- motors, pumps) that provide external world function.
centric” view. Begin by People. Users and operators of hardware and software.
considering all Database. A large, organized collection of information that is accessed via
elements of a system
before you concentrate software.
on 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 exam-
ple, 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 instruc-
tions 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
Complex systems are
actually a hierarchy of a numerical control machine, robots, and data entry devices. Each is a computer-
macro elements that based system in its own right. The elements of the numerical control machine include
are themselves electronic and electromechanical hardware (e.g., processor and memory, motors,
systems.
sensors), software (for communications, machine control, interpolation), people (the
machine operator), a database (the stored NC program), documentation, and proce-
dures. 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 manufac-
turing cell is a computer-based system that may have elements of its own (e.g., com-
puters, 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.