Page 278 - Mechanical Engineers' Handbook (Volume 2)

4 Systems Engineering Methodology and Methods 269

iveness and completeness of a set of issue formulation efforts or requirements. Often, for
example, clients will have difficulty in coping with very abstract formulation requirements
and in visualizing the system that may ultimately evolve. Thus, it may be useful to identify
an initial set of issue formulation elements and accomplish subsequent analysis and inter-
pretation based on these, without extraordinary concern for completeness of the issue for-
mulation efforts. A system designed with ease of adaptation and change as a primary
requirement is implemented on a trial basis. As users become familiar with this new system
or process, additions and modifications to the initially identified issue formulation elements
result. Such a system is generally known as a prototype. One very useful support for the
identification of requirements is to build a prototype and allow the users of the system to
be fielded to experiment with the prototype and, through this experimentation, to identify
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system requirements. This heuristic approach allows users to identify the requirements for
a system by experimenting with an easily changeable set of system design requirements and
to improve their identification of these issue formulation elements as their experiential fa-
miliarity with the evolving prototype system grows.
The key parts of the problem definition step of issue formulation involve identification
of needs, constraints, and alterables and determination of the interactions among these ele-
ments and the group that they impact. Need is a condition requiring supply or relief or is a
lack of something required, desired, or useful. In order to define a problem satisfactorily, we
must determine the alterables or those items pertaining to the needs that can be changed.
Alterables can be separated into those over which control is or is not possible. The control-
lable alterables are of special concern in systems engineering since they can be changed or
modified to assist in achieving particular outcomes. To define a problem adequately, we must
also determine the limitations or constraints under which the needs can or must be satisfied
and the range over which it is permissible to vary the controllable alterables. Finally, we
must determine relevant groups of people who are affected by a given problem.
Value system design is concerned with defining objectives, determining their interac-
tions, and ordering these into a hierarchical structure. Objectives and their attainment are, of
course, related to the needs, alterables, and constraints associated with problem definition.
Thus, the objectives can and should be related to these problem definition elements. Finally,
a set of measures is needed whereby to measure objective attainment. Generally, these are
called attributes of objectives or objectives measures. It is necessary to ensure that all needs
are satisfied by attainment of at least one objective.
The first step in system synthesis is to identify activities and alternatives for attaining
each of the objectives or the postulation of complete systems to this end. It is then desirable
to determine interactions among the proposed activities and to illustrate relationships between
the activities and the needs and objectives. Activities measures are needed to gauge the
degree of accomplishment of proposed activities. Systemic methods useful for problem def-
inition are generally useful for value system design and system synthesis as well. This is
another reason that suggests the efficacy of aggregating these three steps under a single
heading: issue formulation.
Complex issues will have a structure associated with them. In some problem areas,
structure is well understood and well articulated. In other areas, it is not possible to articulate
structure in such a clear fashion. There exists considerable motivation to develop techniques
with which to enhance structure determination, as a system structure must always be dealt
with by individuals or groups, regardless of whether the structure is articulated or not. Fur-
thermore, an individual or a group can deal much more effectively with systems and make
better decisions when the structure of the underlying system is well defined and exposed
and communicated clearly. One of the fundamental objectives of systems engineering is to