p.xii This book is about systems. It focuses on the engineering of systems
and on systems analysis."
p.2 The Elements of a system; Systems are composed of components, attributes, and relationships.
These are described as follows: 1. Components are the operating parts of a system consisting of input, process, and
output. Each system component may assume a variety of values to describe a system state as set by some control action and
one or more restrictions. 2. Attributes are the properties of discernible manifestations of the components of a system.
These attributes characterize the system. 3. Relationships are the links between components and attributes. A
system is a set of interrelated components working together toward some common objective or purpose.
p.5 Physical systems are those that manifest themselves in physical form. They are composed of
real components and may be contrasted with conceptual systems, where symbols represent the attributes of components.
p.14 Engineering activities of analysis and design for human-made
or technical systems are not an end in themselves but are a means for satisfying human wants. Thus, modern engineering
has two aspects. One aspect concerns itself with the materials and forces of nature; the other is concerned with the needs
of people.
p.18[footnote] Engineering is the profession in which a knowledge of the mathematical and natural
sciences gained by study, experience, and practice is applied with judgment to develop ways to utilize economically, the materials
and forces of nature for the benefit of mankind.
p.45-46 IDENTIFICATION OF NEED The systems engineering process begins with the identification of a "need",
"want", or "desire" for one or more new entities, or for a new or improved capability. It should be based on a real (or perceived)
deficiency. For example, a current system may not be adequate in meeting certain performance goals, may not be available when
needed, cannot be properly supported, is too costly to operate, and so on... Defining the problem is the most difficult part
of the system engineering process... Having a definition of need, it is then necessary to (1) identify possible system-level
design approaches in terms of performance, effectiveness, maintenance and logistic support, and economic criteria; and (3)
recommend a preferred course of action. There may be many possible alternatives; however the number must be narrowed down
to a few feasible ones, consistent with the availability of resources
p.91 A model, in this context, is a simplified representation of the real world which abstracts features
of the situation relative to the problem being analyzed... The model used should incorporate the following features.
1. The model should represent the dynamics of the system configuration being evaluated
in a way that is simple enough to understand and manipulate, and yet close enough to the operating reality to yield successful
results.
2. The model should highlight those factors that are most relevant to the problem at hand,
and suppress (with discretion) those that are not as important.
3.The model should be comprehensive by including all relevant factors and be reliable in
terms of repeatability of results.
4.Model design should be simple enough to allow for timely implementation in problem solving...
5.Model design should incorporate provisions for ease of modification or expansion to permit
the evaluation of additional factors as required.
p.143-144 An understanding of the decision-making process usually
requires simplification of the complexity facing the decision maker. Conceptual simplifications of reality, or models, are
a means to this end... Those factors that stand in the way of attaining objectives are known as limiting factors.
An important element of the systems engineering process is the identification of the limiting factors restricting accomplishment
of a desired objective. Once the limiting factors have been identified, they are examined to locate strategic
factors, those factors that can be altered to make progress possible. The identification of strategic factors
is important, for it allows the decision maker to concentrate effort on those areas in which success is obtainable. This may
require inventive ability, or the ability to put known things together in new combinations, and is distinctly creative in
character. The means that will achieve the desired objective may consist of a procedure, a technical process, or a mechanical,
organizational, or managerial change. Strategic factors limiting success may be circumvented by operating on engineering,
human, and economic factors individually and jointly.
p.144 To compare alternatives equivalently, it is important that they be converted to a common measure.
This conversion to a common measure permits comparison on the basis of equivalence.... decisions between alternatives should
be made on the basis of their differences. Thus, all identical factors can be canceled out for the comparison of any two or
more alternatives at any step of a decision-making process.
p.145 Models and their manipulation (the process of simulation) are useful tools in systems analysis...
Models are designed to represent a system under study, by an idealized example of reality, to explain the essential relationships
involved.
p.149 Because of the impossibility of including all factors in constructing the evaluation function [Blanchard
and Fabrycky are speaking of a general mathematical decision model], it is common practice to consider only those on which
the outcome is believed to depend significantly... Although it may be feasible to consider only those relationships
that are significantly pertinent, one should remember that all system elements are interdependent.
p.149 Decision evaluation is an important part of systems engineering and analysis. Evaluation is needed
as a basis for choice among alternatives that arise from design activities, as well as for optimizing systems already in operation.
In either case, equivalence provides the common evaluation measure on which choice can be based.
p.159 A basic human tendency is to focus on the most probable outcome from among several that could occur.
This approach to decision making suggests that all except the most probable future be discarded... this criterion works well
when the most probable future has a significantly high probability so as to partially dominate.
