Page 270 - Mechanical Engineers' Handbook (Volume 2)

2 The System Life Cycle and Functional Elements of Systems Engineering 261

engineering is management technology to assist and support policy-making, planning,
decision-making, and associated resource allocation or action deployment for the purpose of
acquiring a product desired by customers or clients. Systems engineers accomplish this by
quantitative and qualitative formulation, analysis, and interpretation of the impacts of action
alternatives upon the needs perspectives, the institutional perspectives, and the value per-
spectives of their clients or customers.’’ Each of these three steps is generally needed in
solving systems engineering problems. Issue formulation is an effort to identify the needs
to be fulfilled and the requirements associated with these in terms of objectives to be satisfied,
constraints and alterables that affect issue resolution, and generation of potential alternative
courses of action. Issue analysis enables us to determine the impacts of the identified alter-
native courses of action, including possible refinement of these alternatives. Issue interpre-
tation enables us to rank in order the alternatives in terms of need satisfaction and to select
one for implementation or additional study. This particular listing of three systems engi-
neering steps and their descriptions is rather formal. Often, issues are resolved this way. The
steps of formulation, analysis, and interpretation may also be accomplished on as ‘‘as-if’’
basis by application of a variety of often useful heuristic approaches. These may well be
quite appropriate in situations where the problem solver is experientially familiar with the
task at hand and the environment into which the task is imbedded. 1
The key words in this definition are ‘‘formulation,’’ ‘‘analysis,’’ and ‘‘interpretation.’’ In
fact, all of systems engineering can be thought of as consisting of formulation, analysis or
assessment, and interpretation efforts, together with the systems management and technical
direction efforts necessary to bring this about. We may exercise these in a formal sense
throughout each of the several phases of a systems engineering life cycle or in an ‘‘as-if’’
or experientially based intuitive sense. These formulation, analysis, and interpretation efforts
are the stepwise or microlevel components that comprise a part of the structural framework
for systems methodology. They are needed for each phase in a systems engineering effort,
although the specific formulation methods, analysis methods, and interpretation methods may
differ considerably across the phases.
We can also think of a functional definition of systems engineering: ‘‘Systems engi-
neering is the art and science of producing a product, based on phased efforts, that satisfies
user needs. The system is functional, reliable, of high quality, and trustworthy, and has been
developed within cost and time constraints through use of an appropriate set of methods and
tools.’’
Systems engineers are very concerned with the appropriate definition, development, and
deployment of product systems and service systems. These comprise a set of phases for a
systems engineering life cycle. There are many ways to describe the life-cycle phases of the
systems engineering process, and we have described a number of them in Refs. 1 and 2.
Each of these basic life-cycle models, and those that are outgrowths of them, is comprised
of these three phases of definition, development, and deployment. For pragmatic reasons, a
typical life cycle will almost always contain more than three phases. Often, it takes on the
‘‘waterfall’’ pattern illustrated in Fig. 2, although there are a number of modifications of the
basic waterfall, or ‘‘grand-design,’’ life cycles that allow for incremental and evolutionary
development of systems life-cycle processes. 2
A successful approach to systems engineering as an intellectual and action-based ap-
proach for increased innovation and productivity and other contemporary challenges must
be capable of issue formulation, analysis, and interpretation at the level of institutions and
values as well as at the level of symptoms. Systems engineering approaches must allow for
the incorporation of need and value perspectives as well as technology perspectives into
models and postulates used to evolve and evaluate policies or activities that may result in
technological and other innovations.