Unformatted text preview: design toward an optimum.
The basic steps in that process are:
• • • •
• Understand what the system's goals, objectives,
and constraints are, and what the system must
do to meet them—that is, understand the
functional requirements in the operating
Devise some alternative means to meet the
functional requirements. In the early phases of
the project life cycle, this means focusing on
system architectures; in later phases, emphasis
is given to system designs.
Evaluate these alternatives in terms of the
outcome variables (system effectiveness, its
underlying performance or technical attributes,
and system cost). Mathematical models are
useful in this step not only for forcing
recognition of the relationships among the
outcome variables, but also for helping to
determine what the performance requirements
must be quantitatively.
Rank the alternatives according to an
appropriate selection rule.
Drop less-promising alternatives and proceed to
next level of resolution, if needed. This process cannot be done as an isolated
activity. To make it work effectively, individuals with
different skills—system engineers, design engineers,
specialty engineers, program analysts, decision
scientists, and project managers—must cooperate. The
right quantitative methods and selection rule must be
used. Trade study assumptions, models, and results
must be documented as part of the project archives.
5.2 Cost Definition and Modeling This section deals with the role of costs in the
systems analysis and engineering process, how to
measure it, how to control it, and how to obtain
estimates of it. The reason costs and their estimates are
of great importance in systems engineering goes back to
the principal objective of systems engineering: fulfilling
the system's goals in the most cost-effective manner.
The cost of each alternative should be one of the most
important outcome variables in trade studies performed
during the systems engineering process.
One role, then, for cost estimates is in helping to
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