Page 275 - Mechanical Engineers' Handbook (Volume 2)

266 Analysis, Design, and Information Processing

life cycle. In the third phase, these are translated into detailed representations in logical form
so that system development may occur. A product, process, or system is produced in the
fourth phase of the life cycle. This is not the final system design, but rather the result of
implementation of the design that resulted from the conceptual design effort.
Evaluation of the detailed design and the resulting product, process, or system is
achieved in the sixth phase of the systems engineering life cycle. Depending upon the specific
application being considered, an entire systems engineering life-cycle process could be called
design, or manufacturing, or some other appropriate designator. System acquisition is an
often-used term to describe the entire systems engineering process that results in an opera-
tional systems engineering product. Generally, an acquisition life cycle primarily involves
knowledge practices or standard procedures to produce or manufacture a product based on
established practices. An RDT&E life cycle is generally associated with an emerging tech-
nology and involves knowledge principles. A marketing life cycle is concerned with product
planning and other efforts to determine market potential for a product or service and gen-
erally involves knowledge perspectives.
The intensity of effort needed for the steps of systems engineering varies greatly with
the type of problem being considered. Problems of large scale and scope will generally
involve a number of perspectives. These interact and the intensity of their interaction and
involvement with the issue under consideration determines the scope and type of effort
needed in the various steps of the systems process. Selection of appropriate algorithms or
approaches to enable completion of these steps and satisfactory transition to the next step,
and ultimately to completion of each phase of the systems engineering effort, are major
systems engineering tasks.
Each of these phases of a systems engineering life cycle is very important for sound
development of physical systems or products and such service systems as information sys-
tems. Relatively less attention appears to have been paid to the requirement specification
phase than to the other phases of the systems engineering life-cycle process. In many ways,
the requirement specification phase of a systems engineering design effort is the most im-
portant. It is this phase that has as its goal the detailed definition of the needs, activities,
and objectives to be fulfilled or achieved by the process to be ultimately developed. Thus,
this phase strongly influences all the phases that follow. It is this phase that describes pre-
liminary design considerations that are needed to achieve successfully the fundamental goals
underlying a systems engineering study. It is in this phase that the information requirements
and the method of judgment and choice used for selection of alternatives are determined.
Effective systems engineering, which inherently involves design efforts, must also include
an operational evaluation component that will consider the extent to which the product or
service is useful in fulfilling the requirements that it is intended to satisfy.

3 SYSTEMS ENGINEERING OBJECTIVES
Ten performance objectives appear to be of primary importance to those who desire to evolve
quality plans, forecasts, decisions, or alternatives for action implementation:
1. Identify needs, constraints, and alterables associated with the problem, issue, or
requirement to be resolved (problem definition).
2. Identify a planning horizon or time interval for alternative action implementation,
information flow, and objective satisfaction (planning horizon, identification).
3. Identify all significant objectives to be fulfilled, values implied by the choice of
objectives, and objectives measures or attributes associated with various outcome
states, with which to measure objective attainment (value system design).