FOCUS ON DESIGN
rethinking
design theory
A concept borrowed
from psychology gives new perspective to product development.
by Jonathan R.A. Maier
Over the past couple of decades, the field of design theory and methodology has been born literally out of the realization that the process of design can be studied, taught, and practiced using scientific methods. Two widely influential texts propelling the field were Herbert Simon’s The Sciences of the Artificial and Systematic Engineering Design by Pahl and Beitz. An important shift in design thinking advocated by both of these works is that design problems begin at the system level (a whole car, not just a driveshaft). Individual components can be designed only after the whole problem has been understood and defined at the system level and then decomposed into subsystems and so forth, down to individual components that can be designed using the hard engineering sciences and traditional analysis methods. This represents the first major rethinking of design theory since Newtonian mechanics rationalized the design of mechanical components from antiquity.
PROGRAMS IN NEW AREAS
Much progress has been made in new areas opened by the systems level approach
to engineering design. Among these are advancements in our understanding
of decision making, ideation, collaboration, modularity, requirements
modeling, lifecycle considerations, robust design, green design, and various
other “design for x” strategies.
Indeed, the scope of disciplines and problems associated with our understanding
of design has blossomed to the point that the researcher George Hazelrigg
has argued that design is no longer just multidisciplinary, it is omnidisciplinary
in that any and all disciplines may be involved in the solution to a particular
design problem. Similarly, the late researcher Stuart Pugh advocated “Total
Design” wherein every aspect of a design problem must be properly
addressed to arrive at a satisfactory solution.
Meanwhile, as the scope of design research and design thinking has expanded,
the theoretical foundations that our understanding of design is based
on have not been the focus of much attention or progress. There has been
little rethinking of engineering design since the seminal works of Simon
and Pahl and Beitz. Given the increasing scope and rapid progress in engineering
design research, there are those of us who believe it is time to take
a step back and examine the foundations upon which our present understanding
of engineering design is based. It is time to rethink design theory again.
At Clemson University, we have been looking at an innovative method of
design based on a new concept. Interested researchers here include myself
as well as several professors, including Georges Fadel, Joshua Summers,
Grego Mocko, and Dina Battisto. We are studying an approach to design
that we believe goes beyond the idea of function, and gives a deeper and
broader understanding of the issues involved.
Traditionally, it is often stated, or at least implied, that engineering
design is all about function. As the popular engineering textbook Product
Design states, “All products do something. There is some intended
reason behind their existence: the product function.” Such an assumption
dates back to the approach of Newton and Descartes of ascribing deterministic
behavior to machines using mathematics, and it has been extremely successful
and reliable. Function, after all, is easily captured mathematically:
F(x)=y. When a machine performs a function, the design of that
machine is reduced to a math problem.
Things are not so simple in other disciplines that practice design. For
example, in the design of consumer products (industrial design) and the
design of built environments (architecture), it is not the functionality
of the artifacts being designed that dominates. Architects and industrial
designers even dare to speak of the emotion and poetry
of their designs, terms that (gasp) never stain the pages of typical engineering
design texts.
The functional approach is a particularly good fit to the design of traditional
mechanical components, such as shafts, bolts, springs, and the like. Indeed,
the function-based approach of Pahl and Beitz recommends decomposing a
problem down to a level in which individual components can be specified
to embody individual functions.
However, things get a little more interesting when we broaden our scope
to more than just basic mechanical components— that is, when we
look at the system level. For example, what is the function of a bridge?
Or an automobile? What’s more, is the function of a 2008 automobile
far different from the function of a 1908 Model T? Is the function of
a modern steel and concrete highway bridge any different from the function
of the first iron bridge of 1779? The design of automobiles and bridges
has changed dramatically while their function has not.
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| Various design methods integrated with an affordance-based framework. |
The example of a bridge is particularly interesting because as in all
static structures (including furniture, hand tools, artwork, etc.) these
artifacts do not do anything. The “intended reason behind
their existence” is not to transform any inputs to any outputs.
While bridges carry mechanical loads, this is not the essence of their
existence. They carry loads for a larger reason. They allow users
to do something with them. Bridges allow traffic to pass over a river
or gorge. Chairs allow users to sit down. Screwdrivers let users turn
screws.
These examples illuminate a problem of description for the function approach.
The problem stems from the shift in engineering design from the component
level to the system level.
Moreover, problems at this level, including automobiles, bridges, tools,
furniture, appliances, and so forth have another feature in common. They
all involve user interaction. And as the computer scientist Peter Wegner
has pointed out, user interaction is not deterministic and therefore not
algorithmic and not functional. All artifacts allow users to do something
with them, regardless of how much the artifact does itself.
The rethinking of design that is needed now is a conceptual basis that
allows engineers to better describe and solve problems at the system level,
problems that involve user interaction. The concept we propose to deal
with these problems is affordance, a term borrowed from perceptual
psychology and popularized by the psychologist Donald Norman is his book
The Design of Everyday Things.
The affordances of a product are what it provides, offers, or furnishes
to a user or to another product. Most products have a multitude of such
affordances. Automobiles, for example, afford transportation, a comfortable
ride, sporty performance, and so forth. Windows afford a view of the outside
environment and the admittance of fresh air. These affordances, between
artifacts and the people that use them, we call Artifact-User Affordances
(AUA). If we consider a bridge, it allows pedestrians to cross a river
(an AUA), but it also allows cars driven by people to cross. The latter
affordance is between the bridge and the cars, which is an example of
what we call an Artifact-Artifact Affordance (AAA).
An important distinction between the affordances of an artifact and its functions is that the affordances depend on the physical form of the artifact, whereas the functions do not. The fact that functions are form-independent is useful in the design process because it frees designers to choose the physical embodiment that best accomplishes each function. However, the fact that affordances are form-dependent can also be useful, because it allows engineers to analyze and compare the affordances of product concepts (especially at the system level) as well as of existing products for reverse engineering.
POSITIVE AND NEGATIVE
AFFORDANCES
Another useful feature of the affordance approach is that
it is able to describe intended as well as unintended aspects
of the product. For example, a motor’s function is to transform
electrical energy into rotational kinetic energy. Thus, it affords rotary
motion, which is desired and is therefore what we classify as a positive
affordance. However because of the various resistances inside the motor,
the motor also generates heat, which is undesired and is therefore what
we classify as a negative affordance.
By consciously analyzing both the positive and negative affordances of
product concepts during the design process, negative affordances can be
designed against or mitigated. A similar process is not supported by function-based
approaches in which the functions simply capture the “intended”
or desired functionality.
A useful tool allowing engineers to use the additional information captured
by the affordance approach is the Affordance Structure Matrix (ASM), wherein
the system level affordances are mapped to the artifact’s individual
components. ASMs can be prepared for different artifact concepts or existing
products, and then compared to each other or analyzed to attempt to improve
various affordances. The interior of the matrix captures which components
are related to each affordance. Additional detail can be added by distinguishing
whether individual components are either helpful or harmful
in achieving a positive affordance or protecting from a negative affordance.
The left side captures which affordances are related to each other, while
the top captures which components are related to each other as in a traditional
Design Structure Matrix (DSM). The totals on the bottom show how many
affordances each component is related to, while the totals on the right
show how many components are related to each affordance.
There is also room to describe the quality of the affordances of an artifact.
A user can sit on a tree stump just as easily as on a chair. They both
possess the affordance of “sit-ability,” but this affordance
is of higher quality in the chair than in the tree stump. By contrast,
the basic function is the same—to support the user’s weight.
In the case of antique automobiles compared to modern ones, we see that
the basic functionality remains largely fixed over time, while the affordances
have changed rather dramatically. Original positive affordances have been
improved (such as ride comfort), new positive affordances have been introduced
(such as those offered by navigation systems), and negative affordances
(such as noise and pollution emitted) have been significantly reduced.
The affordance approach also offers an integrative framework in which
a larger set of requirements can be captured, including the product functionality,
as well as nonfunctional requirements, such as the aesthetics, marketability,
manufacturability, sustainability, and so forth. Similarly, a wide variety
of recently developed design tools can be tied together in the sense that
they all address specific affordances of a product.
Since the term “affordance” was coined by the psychologist James Gibson almost 40 years ago, the idea has been applied in a variety of fields, including childhood psychology, the design of graphical user interfaces, mobile robots, control room interfaces, and as a bedrock concept for the field of ecological psychology, which Gibson pioneered in the 1960s and ’70s. The application of the concept of affordance to engineering design is a relatively late development.
AUGMENTING TRADITIONAL
APPROACHES
The concept has been attracting increasing attention
as other researchers attempt to overcome limitations of traditional engineering
approaches, while creating bridges to other design-centric disciplines,
such as industrial design, software design, and architecture. Affordance-based
design has sparked interest in places as diverse as Worcester Polytechnic
Institute, the Illinois Institute of Design, the University of Luxembourg,
and Hyundai-Kia Motor Co. I apply it in my own consulting service, Maier
Design Works.
An interesting tool developed by Adriano Galvao, a vice president at Sylver
Consulting in Chicago, in his book Design Relationships: Integrating
User Information Into Product Development is the Function Task Interaction
Matrix, which attempts to identify affordances as the intersection of
product functionality and user tasks.
We are encouraged that other researchers are also engaged in rethinking
some of the fundamentals of design theory. Future frontiers for design
theory in this area are the integration of function and affordance-based
methods, formalisms for identifying affordances, and vocabularies for
naming affordances.
Researchers at Clemson have received National Science Foundation funding
for research into Affordance-based design. The most recent is for a project
led by Gregory Mocko and Georges Fadel, “Integrative Situated Design:
Linking Functions and Affordances Through Form,” which is getting
under way now.
As the theoretical tenets of design are brought up to date with the increasing
demands of systems level design, systems integration, global marketplaces,
new materials, new processes, and other recent demands, we anticipate
continued growth and advancement in the field of design theory that will
benefit all engineers and designers.
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To Read More James Gibson introduced the concept of affordances in the chapter, “The Theory of Affordances,” which was included in his 1979 book, The Ecological Approach to Visual Perception, published by Houghton Mifflin, Hopewell, N.J. The concept of affordances
as it applies to design has been discussed in books and papers.
They include: Maier, J. R. A., T.
Ezhilan, and G. M. Fadel. "The Affordance Structure Matrix
— A Concept Exploration and Attention Directing Tool for Affordance
Based Design,” Proceedings of ASME Design Theory and Methodology
Conference, Las Vegas, Nev. Paper No. DETC2007-34526. Other books on design theory mentioned in this article are: Simon, H.A. (1996). The Sciences of the Artificial. 3rd ed. Cambridge, Mass., MIT Press. Pahl, G. and W. Beitz (1996). Engineering Design: A Systematic Approach. (2nd ed.) New York, Springer-Verlag. Hazelrigg, G. A. (1996). Systems Engineering: An Approach to Information-Based Design. Upper Saddle River, N.J., Prentice Hall. Otto, K. and K. Wood (2001). Product Design: Techniques in Reverse Engineering and New Product Development. Upper Saddle River, N.J., Prentice Hall. Pugh, S. (1990). Total Design: Integrated Methods for Successful Product Engineering. New York, Addison-Wesley. Wegner, P. (1998).
“Interactive Foundations of Computing.” Theoretical
Computer Science 192
(2): 315-351. |
Jonathan R.A. Maier is a research associate
in the Clemson Research in Engineering Design and Optimization Laboratory
at Clemson University. Affordance-based design methods were the subject
of Ph.D. dissertation at Clemson.
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