A Non-Scientific Theory of Design
Philip Sargent
Quillion Systems Ltd.,
St.John's Innovation Centre, Cambridge CB4 4WS, UK
Philip.Sargent@computer.org
Worldview, design science, design theory, shared-memory.
This paper presents a viewpoint of design as intrinsically requiring the integration of techniques from several fundamentally incompatible world-views: distinct "sciences". This implies that there can be no single "design science". The paper also casts doubt on whether a design science, if it did exist, would be useful in the sense of helping to produce better or quicker designs. This entails a short discussion of the distinctions between "complete", "closed" and "adequate" theories. The paper concludes with explicit recommendations to make future designs better and to improve the effectiveness of design processes by enabling design "shared memory". These recommendations follow directly from the strong limits imposed by the proposition that there is no single science of design.
This paper proposes a way of looking at design and at theories of design based on the observation that multiple incommensurate world-views are important. This single hypothesis leads to strong constraints on possible theories of design and, without further elaboration, leads to definite conclusions about the design process and how best to improve it. This is somewhat surprising since this viewpoint (a theory of design itself) is characterized more by the absence of supposition than its presence, and the implications are of the form of what cannot be known rather than what can be deduced. It leads to the conclusion that there can be no unitary "science of design" although any number of empirically verifiable partial theories are possible. It is the unbounded number of such theories which means that a unified science is impossible.
It is a common observation that design, both commonplace re-design of existing products and radical design of entirely new prioducts, involves trade-offs between different goals. These goals may be expressed in entirely different terms, for example the requirement that a car be both fast and safe; or they may be precise but only be capable of evaluation using different principles, such as the requirements that a car body minimize radio-interference and provide mechanical support during motion. These world views are incommensurate because they have no useful points of correspondence in reality except where they interact within a specific designed artefact. This is an operational definition since it depends on there being no useful general correspondences between the different world-views. The term "useful points of correspondance" is necessary because fundamental physics often does provide routes of correspondence between different world views, but the connection is not useful to designers. An illustration is the fundamental connection between moving bodies and electromagnetism as in the car body example: it is special relativity; not a useful body of knowledge for most designers.
This paper advances the hypothesis that reconciling incommensurate requirements is an essential aspect of design, that the design process always requires it1 and designed artefacts must always resolve it , in contrast to recent work by Konda et al.2 where this aspect was held to be typical but not essential. If a single world-view is adequate to a design problem then the goals must have a common representation and thus a common measure of utility. A single utility measure can be calculated and the "design" can be solved completely by optimization techniques.
This definition is circular: I am defining design so that it conforms to the incommensurate viewpoints hypothesis so the validity of this paper rests on whether this definition is defensible and where it is reasonable. It is a useful definition in that it allows certain conclusions to follow; whether it is "true" in any sense is almost impossible to say because different people accept different activities as being "design". However by describing in more detail what these multiple world views involve it is possible to arrive at a number of extensible definitions of design which nevertheless conform to an overall structure. This should enable theorists to state with some precision where their positions lie and so provide a useful means for clarifying debate in design theory.
Designers use many "design idioms", well-known reconciliations of world-views expressed as examples of good partial designs. Examples include bearing design (materials and kinematics), electric motor design (electromagnetism and mechanics) dam design (soil mechanics and hydraulics). Shaw3 has recently used the term "idiom" to refer to specifc architectural designs constructed from multiple techniques, but where the techniques are more similar than the worldviews used here. Her idioms include "table-driven interpreters", "layered hierarchies" and "pipelines": all from software engineering, and all have been discovered or invented by the need to solve real-world problems. Only later have the idioms been recognised, then systematized and appropriate mathematics devised to explore their behaviour.
The view of design theory taken here implies that such idioms are compound bodies of knowledge where the component disciplines have been discovered to be necessary in actual engineering design problems. Large numbers of historical problems have enabled practising engineers to collect and systematize these compound bodies of knowledge and to define the classes of designs for which these idioms are relevant. Once an idiom is discovered, a mathematical engineering analysis technique can often be developed which takes as its boundary conditions the contributing world-views and which may display considerable internal elegance. However there is nothing in the individual sciences of, say, soil mechanics and hydraulics which, in the absence of real, specific dam design problems, implies that any compound body of knowledge exists.
Thus most of the techniques and methods used by designers can be seen to be derived from practice and are not in principle derivable by any kind of design science although the elegance of their reformulation may present that appearance. This is a fundamental reason why the pragmatic approach of "case-based reasoning" (e.g. Bardasz4) is appropriate as a method for constructing designer support tools.
Since any new design could in principle involve individual sciences which have not historically been used together, and since there is no way to be sure that a previously unknown interaction is not going to affect the artefact, there will inevitably be service failures. These failures are important learning situations because they ensure that designers will in their future work properly explore the new design idiom these failures represent and the possibility of failure is part of the culture of engineering5 ("an engineer - someone who turns specifications into malfunctions", MIT t-shirt slogan, Sept. 1991.)
The possible physical effects which will influence a new artefact are not in principle enumerable in advance. Only the designer's imagination, the appropriate use of factors of ignorance6 and exhaustive preliminary testing can help reduce the danger to the public that inevitable failures will entail.
In planning the design process, these unforseeable interactions mean that any particular multiple world-view task can take an inestimable length of time to reach a solution of unspecifiable precision. Any "design science" is therefore strictly limited in its predictive power except in very mature domains using very well established design idioms. In these cases it is arguable whether such a routine process is "design" or whether it is mere form-filling.
Much of the information that is manipulated during design derives not from the initial specification but, as Vincenti says, "from the internal needs of the design itself"7. It is the implications of the specification as manifested in potential artefacts (which exhibit several different sorts of behaviour simultaneously) that produces the raw material on which designers work. Real artefacts can never be completely described by a single discipline so multiple world-views appear as soon as a potential design solution is found. In principle there is no way that a potential solution can be assumed to be valid. There must always be a design analysis stage in which a good idea is evaluated and checked. Typically the idea will arise from looking at the problem from only one or two, perhaps novel, viewpoints, but it must be checked against all viewpoints that can be imagined.8-10 These are often listed as the "-ilities": design for maintainability, assembleability, testability etc. or described by the term DF(X) or "design-for-X".11 The fact that a simple, unprioritized list is always quoted strongly implies that no fundamental classification has yet been found. The purpose of this paper is to suggest that design processes which attempt to incorporate many world-views are inevitably ad hoc. This does not mean that a classification cannot be attempted, but it does mean that any such classification would be not be fundamentally based; though even an arbitrary, standardized classification would be a convenient aid to education, training and research.
A circular hypothesis was advanced earlier defining design as essentially requiring multiple viewpoints and, by implication, including all activities which require this. How well does such a definition match activities commonly held to be "design" and how many other activities does it try to force into the "design classification" ? Before we answer this question I will put forward a potential answer: perhaps it is particular types of design idioms which typify "designerly" activities to us. Perhaps it is not just wrestling with incommensurate problems which defines design, but a particular style of wrestling ? Or maybe we are only willing to admit familiar idioms to the classification of "design" and not others, irrespective of how well they "should" fit according to our definitions. (This last point has to be true in any case since the meanings of words in English are defined socially and not by definition.)
Certain characteristic activities recur whenever multiple world-views have to be rationalized in a single object. The most significant of these is exploration, another is negotiation.
Since there is no a priori way of specifying what the interactions of two different viewpoints might be, the only way to approach the problem is to try something suggested by one viewpoint, see how the object being designed is affected, and then change viewpoint to see how that change is seen from another point of view. Most of the information used in the rationalization of viewpoints is created by this exploratory process. This is indeed a common, perhaps universal, characteristic of activities most people call "design" as the phrase quoted earlier from Vincenti shows7. Instead of proceeding along straight-lines (as suggested by most systematic methods of the Germanic schools) most designers approach their task on a broad front of exploration and retraction,12 what one might call a hesitant "wavefront" of exploration.
Many engineers put stronger limits on what they think of as routine design: the rationalizations between viewpoints must involve some abstract formal reasoning, certainly mathematical and usually numerical. Complexity must arise from the interactions themselves. These must require the use of non-obvious behaviour representations, e.g. Goodman plots, Ashby charts, phase diagrams etc., which require professional training to use (these representations are often recognized as being sufficiently non-obvious and important enough to warrant retaining the name of their originator.). These interactions are individually characteristics of the separate world-views (fatigue initiation, materials selection and crystal structure stability respectively), characteristics also common to any engineering analysis in these world-views, but not characteristics of design.
However the idea that reasoning and exploration produces non-obvious results, which in retrospect are almost inevitable, is generally held to be typical of good design: e.g. that making some part lighter can actually make the whole component stronger, or that one less heat exchanger may enhance rather than reduce operating flexibility. So we have a reasonably common perception of the types of viewpoint interactions (idioms in my terminology) which we are prepared to admit to belonging to engineering "design". There is some evidence for this in software engineering. Early programming was too hit and miss and too simple to be worthy in most engineers' eyes of the name design. Today we have developed a very large armoury of techniques and methods, the process of producing software has become much more complex and only very conservative engineers would object to the phrase "designing a software system".
This is partly why we have such trouble defining "design". Architects and engineers use different sets of idioms, but if one abstracts all the general techniques from those idioms then one arrives at a definition of design that encompasses all problem solving directed at achieving goals; any activity pursued with "intention". This is clearly a wider definition than most people are prepared to accept for design.
By concentrating on multiple world-views whose rationalization requires professional training (intuitive as well as intellectual) and on idioms which already exist because they have been shown to be necessary by practice, we arrive at an open-ended definition which can encompass what we commonly think of as engineering design. (It is still somewhat too broad though.) We can agree that certain identified sets of idioms constitute "design" but we fundamentally cannot lay out criteria for the acceptance of other, as yet unidentified, world view interactions13 because new world views may see the problem in an entirely different way.
As disciplines mature more idioms are developed and completely new activities become admitted to the field of "design" (perhaps "polysaccharide genetic design" in the near future), but none are admitted until there are actual practising designers. This definition of design does not depend on abstract classification of ideal activities but on social acceptance of the worth of professional activity. So writing text-books might be "design" according to my multiple viewpoint principle but because society does not recognise the idiom of text-book construction as an activity worthy of specific professional training, it is not design.
Bucchiarelli14, 15 among others has shown conclusively the central role that negotiation takes in design activities16 There are two kinds: negotiation about meaning and negotiation between competing goals.
If we have multiple world views then each view contains within it one or more incommensurable measures of "goodness", such as fast and safe in the earlier example. Decision theory17-19 has shown conclusively that negotiation of incommensurable goals has to take place in a social framework.
Rationalizing two viewpoints also requires considerable negotiation of meaning15 because each viewpoint classifies the universe in a different way. 20 The term "chip" may mean much the same thing to an electronics manufacturing engineer as to a semiconductor designer, but the boundaries of the classification are different. The manufacturing engineer considers the silicon, metal leads and plastic package as "the chip" whereas the semiconductor designer just considers the silicon. In a novel design, in both mechanical and software engineering, deciding what is a part of what, what is an accessory and what is the main goal of each component, is a major activity.
The multiple world-view approach to design theory implies that team-work and communication are highly important activities. These are part of the design process but their importance comes directly from the way we have looked at the design artefact. This correspondence and influence between artefact and process is not often found so clearly in design theories.
The methods used to enhance team-work: project management, structured meetings, negotiation, room layout, workplace ergonomics etc., are design techniques which are process-centred rather than artefact-centred. However there seems little point in distinguishing between these two classes of techniques because nothing useful comes of it. Warfield13 fundamentally separates these "soft" techniques from the more "hard-science" based techniques but the case for doing so is not firmly based. Designers "do" thermal calculations but they also "do" scheduling and project management. If we did make a fundamental distinction, since we already have multiple world-views for the different "hard-science" techniques, we would need to say that scheduling, for example, represented a different world-view and that the distinction between it and kinematics was itself qualitatively distinct from the difference between, say, kinematics and materials. That seems far-fetched and, more to the point, not useful. Thus in this paper there will be no clustering of world-views into more- or less-similar collections. All distinct world-views have to be considered equally valid in principle (though for any specific design problem some will be more or less relevant).
Given the importance accorded to multiple world views, we need to be a bit precise about what we mean by a single world view: a single "science". Here it is taken to be a mostly closed, coherent and consistent body of knowledge together with a set of techniques and a general approach. The techniques produce results (outputs) which are the same sorts of things as the inputs. (If they produce exactly the same things then the "science" is exactly closed and is termed a "calculus", as in chess where every move takes a position as input and results in a new position.) The techniques and the knowledge in the "science" must be mutually reinforcing (coherent) in that the knowledge explains why the techniques work and manipulating the techniques elaborates the knowledge.
A stress analysis of a solid component takes loads (forces) as inputs and produces stresses as outputs, but at any boundary or feature it is trivial to convert these back into forces. The structural analysis of a pin-jointed structure also uses forces but the techniques are quite different. Thus design of a space-frame uses both these viewpoints: structural for overall elastic stability and stress-analysis to design against plastic yield in the solid joints. These viewpoints are treated as distinct "sciences" because although they share the same general problem solving strategy and although in principle they can both be derived from Newton's laws of motion, the habits of thought in the sets of techniques are different. As an informal proof, one can observe that in universities they are taught in different courses.
Following on from the circular multiple worldview definition advanced earlier, we can identify different definitions of design by adding different restrictions to this over-general definition. Identifying a variety of such definitions is only of any use, however, if we can match each such definition with appropriate theories (which may be partial theories, even within a restricted definition).
The following list of aspects of design have been advanced as being useful to the synthesis of "design science", but I think it is more useful to view them as defining (in an overlapping and not exclusive manner) different types of design activity:
o search
o exploration of emergent information
o decision making
o matching and disposition21
o negotiations concerning trade-offs
o optimization
o planning
o learning
o logical deduction
o solving sets of equations
o teamwork
o constraint management
o production systems 22
o linguistic transformation
o problem solving
o use or construction of idioms
Accepting any one, or a set of, these aspects defines a variety of design for which explanatory theories and useful tools can be devised. Clearly some are dispensable (such as "teamwork" for the lone inventor) but others might be essential for any activity socially accepted as typifying "design" (and I suggest that exploration of emergent information might be one such). A list such as this can be used to distinguish between commonly used categories such as "innovative", "creative" or "routine" design and would work well with current attempts to classify design by 3 orthogonal axes to represent the product and 5 orthogonal axes to represent the process. (For artefact: role of geometry, number to be produced, and magnitude of system, e.g. door-knob to aircraft. For process: activity type, e.g routine to creative, modularity, number of regulatory constraints, type of information flow, number of designers23. This is not a final taxonomy and is already being improved.)
Identifying what are dispensable aspects for specific types of design is itself useful since support for such aspects can be omitted from designer support tools, with consequent savings in tool-development effort.
There are several types of design theory. A popular type is the unified "design science" which some claim to have developed13, 24 and which others see as their goal.11, 23, 25, 26 Alternative theory types are the purely descriptive, which can be divided into (a) those which claim to describe all of the design process (or at least be capable of describing all of it) and (b) those which only claim to describe part of it.
It is often said that we are in a "pre-theory stage" of design research 25 which I interpret to mean that although there are many design science theories there are none which are widely accepted. This paper presents a definitive theory, one that attempts to define design (partially and informally), but is not prescriptive since it has no direct consequences directing how a designer should or should not carry out design.
It is a popular assumption that a "proper" theory of design would be "scientific" (a very contentious and effectively meaningless term2 because of overuse) and would be more or less the same as a "design science". It would:
o guide designers in producing better designs
o help designers work faster
o help organizations manage design and designers more effectively
There is a misconception that a valid theory would inevitably solve design problems: "A set of viable, proven, formal processes for solving all types of design problems will constitute a theoretical foundation for engineering design"11 (my italics), but I hope that the multiple world-views hypothesis shows that need not necessarily be the case. These over-ambitious expectations form very strong constraints on the type of theory being looked for. Dixon (who has been the most articulate in stating these hopes) assumes that any theory which covers all design will have these characteristics, the only grounds for supposing that they will not be satisfied would be that of failing to find any theory which covers all design.25 This is not true. It is entirely possible to develop theories of design which are entirely general, are satisfying from a philosophical point of view, but which are useless in practice to designers (the theory put forward in this paper is perhaps an example). Another view that has been expressed is that any "proper" design theory would be able to put individual design methods on a common metric.24 This is also not true, for the same reasons: because incommensurability is inherent.
Any theory may be adequate in that it explains all the current data, but it still may not be correct (all theories are hypotheses of course). However even if not correct, a theory still shows that there can exist theories of that type.
A theory that is closed covers all the data and all manipulations of the data performed using the theory, and - without addition - would be capable of explaining all such data which may come to light in the future. A closed theory has no scope for expansion (see the description of a calculus above) because all the loose ends have been tied up (often by the wishful-thinking of an overly-tidy mind). However even a closed theory may not have been elaborated fully in that all the implicit truths may not have yet been made explicit. Perhaps a more extreme example of an unelaborated closed theory is quantum electro-dynamics (QED) from which the entire science of chemistry can in principle be derived.
A complete theory explains all the data but does not pretend to be finished, manipulations of the data using the theory produce results which require extensions to the theory. An incomplete theory cannot explain some of the data which, by its own terms of reference, it should be able to. A partial theory only attempts to cover that sub-set of the data explicitly within its scope.
Thus social theories of the importance of negotiation are partial, incomplete theories of design. Warfield's "design science" is a complete, closed theory. The Pahl and Beitz model of design is partial and claimed by some to be complete, those who think the evidence is not strong argue that it is incomplete even over the areas it claims to cover.
Most design theorists only claim publicly that their theories are partial, but many are clearly convinced that their theories are complete. Dissenting data are often classified as being outside the domain of the theory rather than being admitted as counter examples. However that is because we are assuming that our theories are the same kind of thing that are used to describe the simple natural world (physics). Design, as a subject of study, is not alone in this: "Much of computer science includes phenomena about which we do not yet have well-established scientific truths but do have interesting observations and generalizations"3. Indeed, most sciences are like this. Physics is an atypical, rather than an archetypal science and comparisons of any subject with physics with a view to proclaiming it "a science" are usually not useful.
Brooks27 proposed that three types of "result" in software engineering be recognized: (as quoted by Shaw3)
1 findings (well-established scientific truths),
2 observations (reports on actual phenomena), and
3 rules-of-thumb (generalizations proposed by an individual but perhaps not rigorously supported by data),
and further proposed that appropriate criteria for these three be respectively:
1 truth and rigour,
2 interestingness, and
3 usefulness,
and "freshness" for all three. Confusion between these three classes, and especially the application of inappropriate criteria, has lead to great confusion in design theory.
Design may be like any phenomenon in the complex real world. There may be no single theory which covers any observation. Every designed artefact may involve a different set of not just incommensurate technical fields, but a different set of appropriate partial design theories (see Figure 1). As for the natural world we can attempt to map out where different theories work and where they don't, but we should not expect our maps to be exact..
It could be that the only thing common to all design is the intention to produce something useful. That does not mean that design theory and methodology research ends - it means that it is unending.
The view of design as necessarily composed of interacting, distinct world-views does have some useful consequences for design research, and secondarily for designers. It implies that design idioms are precious because they have been hard-won by experience and because they cannot be derived ab initio. Thus the storing and sharing of past design histories, particularly where the design rationale is recorded, assumes a primary importance for design research.8 This would entail research on representations for which indexing and retrieval are easy and selective. The need is stronger than merely recording the rationale behind a specific artefact. What is required is the entire "theory of the artefact"28, the entire range of behaviour of artefacts and partial designs that have been explored by the design process and the discarded. This would thus comprise as complete a description as possible of the design idioms, including novel idioms, used in the derivation of the artefact design.
Retaining the shared knowledge of an established design team is also seen to be of primary importance. Any methods that encourage team-work without reducing the variety of viewpoints are valuable. This reflects current thinking in manufacturing engineering and engineering management29 but whereas those disciplines base their thinking on observations, here we derive the same principle directly from thinking about design theory.
Although this paper has concentrated on teams of designers the same considerations affect the thoughts inside in the head of a lone designer. He or she must integrate and trade-off multiple world-views of the same problem. So techniques should be devised which enable single designers to manipulate (play with) ideas using different disciplines at the same time, yet preserve some consistency in the underlying artefact description. Consistency must be maintained (at least partially) even though modifications may be made by distinct, largely incompatible methods. There are clear implications for software research in multiple database update techniques, product model architectures, goal-oriented programming, user interface design30 and design environment tool integration.9, 31 We should be aware, however, that incompatibilities may not be noticed or fixed for the same reasons that failure can occur in practice: it is in principle impossible to enumerate all possible interactions.
When attempting to devise new design idioms for new types of artefact it is useful to try to find a small set of different disciplines that give world-views which are as different as possible while retaining as great a similarity as possible in the underlying representations. The former gives the expressive power, the latter means that each view informs the other about something relevant. This may involve the search for new representations and, typically, this is indeed how new design techniques come to light: the Gantt chart, the Ashby materials selection chart32 or the HeapSort algorithm33 all rely on a novel representation which can be manipulated from multiple, different viewpoints.
Lastly, this view of design theories can serve as a test for snake-oil salesmen. Design and the "product development process" are now seen as industrially very significant and companies are spending very large sums of money investing in new organizational systems. This supports a large industry of consultants with an attendant fringe of methodologists. Some of the more mystical and charismatic of these design theorists can actually do much good since much of the improvements to be gained only arise from convincing large numbers of people. However, when some practical bundles of techniques make a bid for formality and academic respectability, then we need some criteria by which to classify and judge them. I propose that any methodology or model which claims to be totally unified, coherent, consistent and complete should be treated with caution.
There can be no unified "science of design" if an essence of design is the rationalizing and assimilating of multiple incommensurate "sciences". However the absence of any such theory is itself useful because it indicates which areas of design study require pragmatic support.
Chasing after an illusionary "design science" is observed to be more a characteristic of engineers seeking enhanced status as physical scientists rather than emphasizing design creativity - which this paper among others2, 34 show to be qualitatively different.
I wish to thank Eswaran Subrahmanian, Suresh Konda, Ira Monarch, Rob Coyne and David Steier particularly for many intriguing and argumentative weeks during my visits to EDRC, Carnegie Mellon University, to Ken Wallace for constructing an environment so conducive to the study of design theory within the Engineering Dept. at Cambridge University and to David Brown, David Ullman and Richard Coyne for conversation while they were visiting Ken's design centre. Many thanks too to Jintae Lee, Lukas Ruecker, Steven Eppinger, Don Clausing, Louis Bucciarelli, Warren Seering, Howie Shrobe, and Hal Abelson at MIT and Mark Cutkowsky, Larry Leifer and Fred Lakin at Stanford for so politely answering my naive questions and lastly I wish to thank all the participants at John Gero's 2nd. Intl. Round-table Conference on Computational Models of Creative Design for many hours of fascinating discussion and to the Key Centre for Engineering Design (Sydney University) for a travel subsidy to attend.
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Design Studies 15 (4) 389-402 October 1994
Cambridge University Engineering Department
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