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CHAPTER 10 SYSTEM ENGINEERING 249

design, and construction of a targeted system element is initiated. At the top of the
hierarchy, a very broad context is established and, at the bottom, detailed technical
activities, performed by the relevant engineering discipline (e.g., hardware or soft-
ware engineering), are conducted. 2
Stated in a slightly more formal manner, the world view (WV) is composed of a
set of domains (D ), which can each be a system or system of systems in its own right.
i
WV = {D , D , D , . . . , D }
2
1
n
3
Each domain is composed of specific elements (E ) each of which serves some role
j
in accomplishing the objective and goals of the domain or component:
D = {E , E , E , . . . , E }
2
i
3
1
m
Good system
engineering begins Finally, each element is implemented by specifying the technical components (C )
k
with a clear that achieve the necessary function for an element:
understanding of
context—the world E = {C , C , C , . . . , C }
k
j
3
2
1
view— and then
progressively narrows In the software context, a component could be a computer program, a reusable pro-
focus until technical gram component, a module, a class or object, or even a programming language state-
detail is understood. ment.
It is important to note that the system engineer narrows the focus of work as he
or she moves downward in the hierarchy just described. However, the world view
portrays a clear definition of overall functionality that will enable the engineer to
understand the domain, and ultimately the system or product, in the proper context.
10.2.1 System Modeling
System engineering is a modeling process. Whether the focus is on the world view
or the detailed view, the engineer creates models that [MOT92]
? What does a • Define the processes that serve the needs of the view under consideration.
system
engineering model • Represent the behavior of the processes and the assumptions on which the
accomplish? behavior is based.
3
• Explicitly define both exogenous and endogenous input to the model.
• Represent all linkages (including output) that will enable the engineer to bet-
ter understand the view.

To construct a system model, the engineer should consider a number of restraining
factors:

2 In some situations, however, system engineers must first consider individual system elements
and/or detailed requirements. Using this approach, subsystems are described bottom up by first
considering constituent detailed components of the subsystem.
3 Exogenous inputs link one constituent of a given view with other constituents at the same level or
other levels; endogenous input links individual components of a constituent at a particular view.