Decision Based Design Position Paper

David G. Ullman
ullman@engr.orst.edu

Professor
Department of Mechanical Engineering
Oregon State University
Corvallis Oregon, 97331
Phone: 541-737-2336
Fax: 541-737-2600
Url: http://www.engr.orst.edu/~ullman

Design is the social activity focused on the development of product information punctuated by decisions. Most decisions are made by teams or individuals based on incomplete, conflicting, qualitative, interdependent information which is beingrefined and reorganized during deliberation. In most design problems, the alternatives, and the criteria for the evaluation of the alternatives= attributes, evolve as work progresses. There is no confirmation that either the alternative set or the criterion set is complete even after a decision is made. The problem is always open to new alternatives and criteria. Team members seldom itemize the entire set of potential alternatives and even when using a system such as Quality Function Deployment they are never assuredthat they have addressed all the criteria. Usually all the alternatives are not evaluated against all the criteria by every member of the design team. This isespecially true if the team is multi-disciplinary. Completeness of assessment is often tied to the team members predilections. There are two types of predilection commonly shown by team members. When a team member is strongly biased toward a particular alternative then s/he is referred to as the alternative=s champion. When a team member expresses a particular view through weighting or ordering the criteria, s/he is considered to have a specific view of the decision problem. All team members have a specific view and some are champions for a specific alternative. In the ideal world each team member would be an expert and could evaluate how well each alternative met each criterion with authoritative knowledge.

However, this is seldom the case and decisions are usually made with less than expert knowledge. Informally, knowledge is a measure of how much a team member knows about an alternatives = attribute relative to the target set in the criterion. During design activities knowledge is generally increased (i.e evolved) by building prototypes, performing simulations (analytical and physical) or finding additional sources of information(e.g. books, vendors, experts, consultants). Each of these activities to increase knowledge requires the commitment of resources such at time, money and expertise. These resources are usually carefully managed are the chief determinants ofwhen a final decision has been made (i.e. when out of time or money, engineers have to stop making changes). For a majority of design problems there is no numerical analysis possible to support the decision making process. There are two reasons for this. First, usually some of the attributes of a Agood@ solution are qualitative and can not readily bereduced to equation form. Second, methods like utility theory and optimization are hard pressed to model the complexity necessary for many design problems. This is not to say that analysis is not an important part of decision making. As stated in the paragraph above, analysis plays a major role in the evaluation of alternatives relative to criterion increasing the decision makers knowledge about the alternatives. In order to support design decision making, the cognitive strategies people use to make decisions as individuals and teams must be studied. Based on this foundation, methods must be developed which reach beyond the current value and utility methods, optimization, and fuzzy methods to support designers in a wider range of activities. Modeling decision making activity is complex beyond what is now understood and thus support for this activity is still immature. Current research is focused on modeling decision making in individual and team activities through the study of industrial projects and the use of a model of decision making to support the capture, management and query of a design rationale system.