Page 296 - Mechanical Engineers' Handbook (Volume 2)

5 System Design 287

It is certainly possible that the product, or system, that results from a systems engineering
effort may be used as a process or life cycle in some other application. Thus, what we have
to say here refers both to the design of products and to the design of processes.

5.2 Operational Environments and Decision Situation Models
In order to develop robust scenarios of planning and design situations in various operational
environments and specific instruments for evaluation, we first identify a mathematical and
situational taxonomy:

• Algorithmic constructs used in systemic design
• Performance objectives for quality design
• Operational environments for design

One of the initial goals in systems design engineering is to obtain the conceptual specifi-
cations for a product such that development of the system will be based on customer or
client information, objectives, and existing situations and needs. An aid to the process of
design should assist in or support the evaluation of alternatives relative to some criteria. It
is generally necessary that design information be described in ways that lead to effective
structuring of the design problem. Of equal importance is the need to be aware of the role
of the affective in design tasks such as to support different cognitive styles and needs, which
vary from formal knowledge-based to rule-based to skill-based behavior. 31 We desire to
design efficient and effective physical systems, problem-solving service systems, and inter-
faces between the two. This section is concerned with each of these.
Not all of the performance objectives for quality systems engineering will be, or need
be, fully attained in all design instances, but it is generally true that the quality of a system
or of a systems design process necessarily improves as more and more of these objectives
are attained. Measures of quality or effectiveness of the resulting system, and therefore
systems design process quality or effectiveness, may be obtained by assessing the degree of
achievement of these performance criteria by the resulting system, generally in an operational
environment. In this way, an evaluation of the effectiveness of a design decision support
system may be conducted.
A taxonomy based on operational environments is necessary to describe particular sit-
uation models through which design decision support may be achieved. We are able to
describe a large number of situations using elements or features of the three-component
taxonomy described earlier. With these, we are able to evolve test instruments to establish
quantitative and qualitative evaluations of a design support system within an operational
environment. The structural and functional properties of such a system, or of the design
process itself, must be described in order that a purposeful evaluation can be accomplished.
This purposeful evaluation of a systemic process is obtained by embedding the process into
specific operational planning, design, or decision situations. Thus, an evaluation effort also
allows iteration and feedback to ultimately improve the overall systems design process. The
evaluation methodology to be described is useful, therefore, as a part or phase of the design
process. Also, it is useful, in and of itself, to evaluate and prioritize a set of systemic aids
for planning, design, and decision support. It is also useful for evaluation of resulting system
designs and operational systems providing a methodological framework both for the design
and evaluation of physical systems and for systems that assist in the planning and design of
systems.