Page 281 - Mechanical Engineers' Handbook (Volume 2)

272 Analysis, Design, and Information Processing

attribute tree that represents those aspects that will be formally considered in the
evaluation and prioritization of a set of proposals.
• Causal loop diagrams, or influence diagrams, represent graphical pictures of causal
interactions between sets of variables. They are particularly helpful in making explicit
one’s perception of the causes of change in a system and can serve very well as
communication aids. A causal loop diagram is also useful as the initial part of a
detailed simulation model. Figure 7 represents a causal loop diagram of a belief struc-
ture.
Two other descriptive methods are potentially useful for issue formulation:
• The system definition matrix, options profile, decision balance sheet, or checklist pro-
vides a framework for specification of the essential aspects, options, or characteristics
of an issue, a plan, a policy, or a proposed or existing system. It can be helpful for
the design and specification of alternative policies, designs, or other options or alter-
natives. The system definition matrix is just a table that shows important aspects of
the options that are important for judgment relative to selection of approaches to issue
formulation or requirement determination.
• Scenario writing is based on narrative and creative descriptions of existing or possible
situations or developments. Scenario descriptions can be helpful for clarification and
communication of ideas and obtaining feedback on those ideas. Scenarios may also
be helpful in conjunction with various analysis and forecasting methods, where they
may represent alternative or opposing views.
Clearly, successful formulation of issues through ‘‘asking’’ requires creativity. Creativity may
be much enhanced through use of a structured systems engineering framework. For example,
group meetings for issue formulation involve idea formulation, idea analysis, and idea in-
terpretation. The structure of a group meeting may be conceptualized within a systems en-
gineering framework. This framework is especially useful for visualizing the trade-offs that

Figure 7 Causal loop diagram of belief structure in a simple model of urban dynamics.