Keynote Papers Design Philosophy: The State of the Art

Hiroyuki Yoshikawa ( l ) , the University of Tokyo

This paper deals with an investigation on the state-of-the-art of the design philosophy or the design theory. This investigation was planned by the STC Design in tho occasion of General Assembly of CIRP, held at Tokyo, 1988. A questionnaire was sent to every member of CIRP in September 1988 and a revised version of it was sent to DN members in March 1989. The author received ten answers, all of which are very valuable. In this paper, the questionnaire with some comments were quoted in Chapter 2. In Chapter 3 the result of the analysis of those answers is reported. In Chapter 4, some well known proposals of the design methodologies are introduced discussing the connection with the CIRP responses. In Chapter 5, investigating the general natures of the design methodologies, a framework of the design theory is depicted. A general design theory based on the framework is shown with its capability and limitation. Future developments of such theories are suggested.

ABSTRACT:

KEYWORDS: design philosophy, design theory, design methodology, desigrdmanufacturing integration, topology, logic, CAD/CAM

1. INTRODUCTION

Recently, the design has attracted a considerable attention of various researchers. Of course, there are many designers in every field of technology. Architects. machine designers, designers of electronic circuits, and recently we find designers of software and designers of material. They spread widely and work rather independently without communicating through different fields. One of the main concerns of the researchers is this point, that less commonalities are found and discussed among designs of different fields due to the lack of communication. There is a fundamental question: Why do designs appear so differently although they should be based on a unique capability of the human beings? This question urged some researchers to establish general design theories. First, they tried to extract methodologies that were usefully applicable to designs of different fields, that is universal methodologies. Secondly they tried to develop them into general design theories.

Frankly, the results of those trials have not been sufficiently appreciated by designers, although there are not a few cases of successful application. They are still some cases and not all. However, the trend seems changing quickly because of the circumferential changes of design: they are increase of the burden upon designers to innovate new products, the complexity of design requirements, the systematization of design knowledge, the integration of design with the manufacturing etc. The effective approach to cope with these problems must rely on the knowledge about what design is. This is the very subject of the general design theory. Before introducing the recent trends of design theories, we shall investigate the state-of-the-art in the CIRP world.

2. QUESTIONNAIRE

Questionnaire with some comments were sent to DN members of CIRP. Here, the whole sentence is quoted.

CIRP Ouest ionnaire on Design PhilosoDhv lor Desim Theory) We are confronted with some problems concerned with design.

They are as follows:

1. Traditionally, we thought that the design technology and the manufacturing technology are different from, and sometimes independent of, each other. The design technology is based on the relevant knowledge particular to the specific technological field, such as mechanical, electrical, aeronautical, naval engineering or any. On the contrary, manufacturing technology has been thought considerably common through those fields. Therefore, in the CIRP world, more research efforts have been paid for manufacturing technology and less for design. But recently, due to the increasing importance of integration of design and manufacturing, it has been widely recognized that finding common natures of design through different fields is crucial. Especially, when thinking of CIM, design is recognized very important as one of the major sources of information in the whole information processing system, that is extensively affecting the total efficiency of the system.

2. In designing of both products and manufacturing systems, creativity is highly requested for designers. Under the quickly changing circumstances of the economy, society and environments, the designers must create new type of products

and systems continuously. Creativity of designers may be improved by the engineering education and the appropriate assisting systems for designing. For these purposes, establishment of the design philosophy (or theory) are highly appreciated.

Recently, the importance of design work has been increased in various fields because the market demands more variety of industrial products. High quality of design and high efficiency of design work are the keys to meet the demands. This brings about necessity for more assistance of computer to designers. Development of the new-type CAD is highly expected.

The high performance of recent products is considerably dependent on the integration of different-type elements, such as mechanics, electronics, optics etc. Mechatronics is a good example. This causes a new problem to the design, that the cooperation and mutual understanding among designers of different fields are essential. Methods of bridging those different fields and of organizing them are expected.

From these problems, it is concluded that a theoretical or philosophical aspect of design will be or already has been very important for further development of design technology. Let us define an academic field which is devoted for getting the answer to these problems as design theory. The design theory will be devoted to elucidate what design is and hopefully will output knowledge useful for those practical problems. With a mind to the above-mentioned brief definition of the

design theory, please reply the following questions.

Q.l. When conducting your research, such as development CAD/CAM systems, of process planning or of manufacturing systems; techniques of processing or measuring; standards for products; or any, it Seems reasonable that you have a premise explicitly or implicitly that concerns the definition of design: that is what design is, how design is conducted. what knowledge operates during designing etc. These are objects of the design theory. Please let us know what kind of design theory you do have: Is it your own home-made design theory, or some theory established by a design theoretician? Please explain the theory briefly.

Q.2. When teaching the design for students or young engineers, especially aiming at improving their creativity we occasionally feel lack of systematic methods for teaching. In order to improve the efficiency and quality of teaching design, it seems useful to provide teachers with good design theory. Do you have such design theory applicable or do you have a plan to develop one?

Q.3. Recently, number of researchers who are interested in developing so-called intelligent CAD is increasing rapidly. It is aimed to assist designers not only in drafting phase of the design process. but also conceptual design phase. Strangely, however, most researchers interested are from the information- processing field, who are not familiar with mechanical engineering. Therefore, the cooperation of the.mechanica1 engineen to those people is crucial. But it is not easy at present, due to lack of.the theoretical presentation of designing process. Empirical know-how of machine design is hardly

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comprehensible to the information-process people. Questions are as follows: (1) Are you interested in such intelligent CAD? Do you think that it is necessary? (2) Do you have some contact with information-processing experts who are interested in the intelligent CAD? (3) If so, what is your method with which you let them understand what machine design is? (4) Do you think that the design theory is useful as one of the methods?

4.4. In spite of widening and deepening of basic research works on human intelligence in the fields of artificial intelligence and cognitive science, less attention has been paid to the human intelligent activities in engineering, such as design and other various types of decisions in manufacturing. They are, however, ones of the most important and typical intelligent processes in the modem society. Therefore, contribution of CIRP Members to those fields will be highly expected. Again, it will be of importance to elucidate the human intelligence in the design and manufacturing, that is the design theory would be well established. Do you have any activity or plan of cooperating with the specialists of the artificial intelligence and/or cognitive science for promoting this basic research? If so, what design theory do you use for this propose?

3. CLEAR ANSWERS TO UNCLEAR QUESTIONNAIRE

3.1 Design theory

Readers may have an impression that the questionnaire quoted in the last chapter is not enough certain to answer rigorously. This uncertainty comes from the inexact definition of “design theory”. It seems laborious to answer. CIRP Colleagues, however, were patient and cooperative, giving clear answers to the unclear questionnaire.

Before going into the design theory or philosophy. we must take up the design itself. Merchant [A] stressed “The basic premise of (Merchant’s) philosophy (of design) is that design is an inseparable part of the overall technological system of manufacturing and provides the primary source database for all other activities that go on in that system.” This point is very important from both viewpoints; practical design and design theory. It is easily understood only by considering examples. In design of a turbine, a machine tool, a flower bed or any, it is essential that the result of the design must be realized as an existence in the real world. Anything that is not realizable is not a design but a dream, although the latter is important sometimes as a powerful incentive for creating an innovative design. The realizing activity is manufacturing. Therefore, the design activity must be conducted under a strict condition that it is possible to manufacture, or constructively the design must be concomitant with the practical manufacturing methods. This point is stressed by Boothroyd [A] in a very sophisticated way and he actually established a method useful for the design activity and for the design education.

From the theoretical point of view, designing is a human thought process distinguished from others by its nature that the physical realizability of the result of the thought is a necessity. In general research of the thought process, artificial intelligence for instance, the physical realizability is out of consideration, or timidly consider as semantics. Therefore, the design, when considered the concomitancy with the manufacturing, is an intrinsically independent target of the research on human intelligence.

The level of the design theories. however, is not sufficiently high in spite of its uniqueness if established. The recent history of the development of the design theories will be introduced in the following chapter, and we shall see many kinds, but unfortunately the applicability of those theories are not widely appreciated and remains at limited occasions.

Peters [A] says “We do not believe in theories established by design theoreticians.” He “prefer(s) the term design philosophy or better design methodology.” He pointed out “the electricians never see what happens with electric-current and must rely on abstract models well established on the base of theory. They need a design theory.” But “mechanical designers need a method.” It is true that we are not provided with a consistent theory of the mechanical system. For instance, we do not have a system theory of machine similar to the Kirkhoff‘s theorem in the electric circuit. An excellent study was conducted by Bjerke [2], but the result does not yet cover all the mechanical functionalities concerned in a constructivistic sense. This is the reason why Peters insists that the mechanical designers need “methods” that guide us along certain steps of design. Those steps might be automatically deduced from

theories in the case of electric circuit design, but it is not the case for the mechanical design. Thus, Peters proposes a home-made design methodology which was established through his own experiences of mechanical design, education and consideration of manufacturing factors.

As mentioned in the following chapter, there are not a few design theoreticians who proposed design methodologies of a category similar to Peters’ methodology. But the main difference between them are the implied universality of methods. Many of design theoreticians claim that their methods are applicable universally to any kind of design. However, many users feel that the universality deteriorates the usefulness.

In order to escape this dilemma, is there any useful method? Our Colleagues contributed three kinds of interesting proposals.

Corbett [A] examined many methodologies publicly known. and concluded that they are not universal. His proposal is to limit the functionality of a design methodology for keeping its universality. He mentioned a method, called DTC: designing to the cost. This is a method to organize designers to a team and manage the whole design activity. Substantially it is a management method, therefore does not concern the thought process of each designer. But owing to the neglect of the thought process of design, this method can preserve high universality.

A steady approach was reported by German Colleagues, Weck [A] and Dahl [A]. German-speaking countries are known remarkable in the development of many design theories. Dahl mentioned “During the last two decades a lot of design theories were developed, which were often compared in literature. The goal of these elaborations were to find out common aspects and to standardize them.” Actually they accomplished a standard, VDI- Directives 2221 and 2222. Anyone will agree that this kind of approach bears high propriety.

A very interesting contribution was from Pruvot (A]. Let us start with his statement “Machine design is an empirical process - in fact it is not true, it is only arbitrary - because people didn’t have either education or knowledge to do better. But at least for the kind of machines I know as a professional design engineer, it is very easy to find a true scientific method for designing them”. If we follow him we can deduce that a universally applicable theory or methodology will be available when we achieve a universal ability of design.

Pruvot’s method of establishing a design science is substantially an introspection. The real design theory exists in his thought. This reminds me of Des Cartes. His proposal implies very important issues. He refuses the idea that the design process is observable in a sense as the physical process is observable. It is true that wc are lack of appropriate methods for the observation of human thought processes. Science is based on the observability. Without it, we must start with the introspection as a philosopher. Therefore, a Cartesian Pruvot is right as a founder of design science which will be developed in the future.

His method is called by himself Constructive Deduction. Constructivism may be one of the most important standpoint for engineers. In usual mathematics, there are many theorems that insist existence of something. The set of points as such converges into a point, for instance. But many of them do not indicate practical methods of operation; converging procedure for instance. In constructive mathematics, it is obliged for a theorem to bear the operation. Thus, the result is that A v 7A does not always hold. It is true in many engineering problems. Design theory may be useful when it is described in a way of constructivism. In other words, a theory will include a method explicitly, that is practically useful for the design activity.

3.2 Education and Creativity

The majority of the answerers think that students improve the designing ability through actual experiences. Needless to say, the designing ability is one of the most important power for an engineer in any field of technology. However, if we compare the weights of design education in the curricula of university departments, we shall surprisingly find the differences. For instance, the weight is very high in the department of mechanical engineering and low in that of electrical engineering. This can be attributed to the fact, as pointed out by Peters [A], that students of electrical engineering may achieve the design ability implicitly through learning the theory of electrical engineering, but students of mechanical engineering can not, and need to learn the method of design independently and explicitly.

Then, what kind of experience can lead students to able

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designers efficiently? Peters’ answer is very helpful. He shows good examples of design experience. They are electric switches, machine frames, cars etc. These examples are familiar for students and thus easy to think, analyze, reform, improve and design by their own knowledge and systematically. But. Peters says “Teachers are telling the students: Design a turbine or a compressor. The students never saw! Or design a spindle, giving up torque and power and speed. Students never saw what it is used for. how it is assembled or manufactured.”

Corbett [A] emphasizes that the learning environment is an important factor. He proposes to let students participate a design team. Through contacts to design experts, they shall learn significant elements of design, the balance of methodical and creative for instance, which they can never learn in isolation.

Weck [A] thinks in a similar way. “In order to improve the efficiency and quality of teaching design, a lot of case studies of detailed machine tool designs are given to the students.” Lecturers give the explanation, and the students learn to design in small groups. “The general theory underlying this approach is that the students learn from the experience of experts.”

Under the circumstance that the design theory, even if it exists, can not include methods in it explicitly or implicitly, or it can not automatically generate useful methods, the education of design must rely mainly on empirical way. In other words, the problem concerns the possibility of establishing a design theory that generates practical methods. This will be discussed in the following chapter.

3.3 CAD/AI

Many of the answerers mentioned their interests in the intelligent CAD, but practical applications were not reported. As Davies [A] pointed out, his application of the artificial intelligence technology to the manufacturing field has reached some extent and he has some images about the intelligent CAM, but the extension of the trial into the design field seems extremely hard and thus none can say definitely about the image of the intelligent CAD. Now, it may be the time when we start discussing the images of the intelligent CAD for the future development.

Some directives were mentioned in the answers. Dahl [A] suggested that the design morphology, proposed in many of the design theories, can be a kind of model of the artificial intelligence. A designer utilizes different components of knowledge when designing. The knowledge may be stored in a database. Further, the designer must organize those components into a complicated system for completing the design. In organization, the knowledge of combining two different components is requisite. The combination may be represented as design rules in CAD. He proposed a system called Intelligent Design Assistant.

Peters [A] emphasizes the necessity of an appropriate work division between mechanical engineers and information-processing engineers. He insists that CAD systems developed by the information-processing people always fail to be practical because of their too much limited number of elements and simple shapes adopted in their systems. For instance, he says ‘‘ Databanks must be set up b o t f o m up from the workshop floor, and with the cooperation of people of the floor.” Knowledge of manufacturing is still in the brains of manufacturing engineers and not described explicitly on the readable documents. Information-processing people can not enter into this world, so they “must study the databanks management systems suited for designers.“

Davies and Atkinson [A] pointed out an interesting aspect. Usually design theories are lack of a theory on the man-computer interface. It may be the most important part of design theories, if they are useful for constructing good intelligent CAD systems, that deals with a process by which unstructured inputs of requirements are transformed into a well structured design. Yes, this aspect must be a central concern of design theories.

Generally, as for the cooperation of CIRP people and A1 researchers. answerers think that the cooperation will be possible and necessary. Many think that CIRP people can give the interesting and important resource to the A1 researchers.

4. BRIEF SURVEY OF DESIGN METHODOLOGIES

systematic composition into an innovative design process. Therefore their usefulness to the professionals and the students were remarkable and actually they were used. They were not design theories but methodologies. The development of design theories will be discussed in the next chapter.

Here, we shall start with a categorization of methodologies. Almost of design methodologies have been described in terms of empirical words and not of scientific words. Therefore, the proposition or the assertion is usually presented without a proof. More precisely, they substantially reject the verification. They need not be verified by others because their truth is already guaranteed by themselves, authors. They are the collection of facts and thus not an object of verification. They don’t care that the contradictory propositions appear in different methodologies. and never try to compromise them in order to establish a unique methodology. Methodology is something like this. Therefore, we need a categorization. Each category may be called a school of design philosophy.

(1) Semantics School This school was founded by Rodenacker [8]. Central dogma of

this school is that any machine, as an object of design, is something that transforms the inputs of three types: substance, energy and information into the outputs of three types respectively, which have different states to the inputs. The differences between the inputs and the outputs are called functionality. The initial requirement is given in terms of the functionality. The design starts with this functionality. Then, the functionality is analyzed into a logical structure, which gives connections between sub-functionalities. Fig.1 shows an example. Each block shows a sub-functionality that locally transforms substance, energy and information. After decomposing the initial functionality into sub-functionalities small enough, then the designer substitutes them with particular physical phenomena that realize the transformations respectively. Rodenacker emphasized the importance of collecting the correspondence between the functionality (transformation) and physical phenomena systematically. Fig.2 is an example.

There are many researchers who may belong to this school, especially in Germany and Switzerland. Roth [lo] is a leader of Braunschweig group who developed a system called AKK (Algorithmischen Auswahlverfahren ziir Konstruktion mit Katalogen) along with the philosophy of this school.

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C o m n nf F- Corr- Tables obtained in this approach are useful not only for

designers practically, but can be implemented as databases in CAD.

functionality, the physical phenomenon and the function canier that is sometimes machine elements. He implemented it into a CAD

As pointed out in the last chapter, there have been many researchers who tried to generalize the designer’s design activity

activity of professional designers and for educating students. Those textbooks elaborate the elements of design activity and their

for making textbooks that are for improving the design Ott 161 proposes a table that shows the relationship among the

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system.

(2) Syntax School When we try to develop a design method applicable to any field

of technology, it becomes difficult to stick to the semantical aspects of design objects, because we don’t have good means to deal with the semantics in a systematic way. In this case, more attention shall be paid to the procedural aspects of designer’s design activity than the design object itself. This might be said that a dynamical or temporal aspect is abstracted from design neglecting the static aspects of design that was emphasized in the Semantics School.

Feasibility Study

Phase I1 PrcliminaryDesi n

Detailed Design

Planning for production m Planning for disuibution F i , Plannin for consum tion

Phase Vn Plannin for retirement r a

Asimov [ l ] is one of the leaders in this school. He proposes a design morphology shown in Fig.3. Usually, more detailed morphologies are shown practically which will be good directives for designers.

As seen easily, this philosophy is not contradictory to that of the Semantics School. On the contrary, they indicate two important aspects of the design activity respectively, that is statics and dynamics, and therefore both will be combined to achieve the more sophisticated design methodology.

Actually some methodologies that include both aspects and thus with improved usefulness have been proposed. Pahl and Beitz [7] are representing this approach. They introduced a concept of the hierarchy shown in Fig.4, improving the approximation to the thought process of the designers. SADT (Structured Analysis and Design Technique) is another example proposed by Ross [9].

(3) Historicism School Many of design methodologies proposed are more or less based

on a premise that the universality of a method is improved by abstraction. Perfectly universal method is a target of researchers of the design methodology. As was pointed out in the last chapter, however, many of the methodology users feel that universality and practical usefulness are .contradictory. More critically, there is an opinion that the creativity of a designer will deteriorate with the methodology.

From such criticism, a doctrine was derived. For instance, we can learn it by Fuchs’ philosophy [4]. He emphasizes the significance of the case history of design, which include all necessary knowledge to leam for improving design ability. He tells us an analogy: How can one learn cooking a fried egg? If you give one a textbook that explains the protein chemistry, the theory of heat transfer, the theory of digestion etc., all necessary to scientifically understand the cooking process of an egg, one may produce huge

numbers of charred eggs. A design ability can never be achieved efficiently by theoretical manner. There seem to be many supporters of this philosophy at present.

(4) Psychological School In the psychology, there is a domain called psychology of

creativity. This appears very attractive for us who are interested in promoting the creative design, but unfortunately researchers of this field are only interested in the elementary education and not in engineering education. Creativity engineering is another field of psychology. They are, however, too subjective and idiosyncratic. Future development is expected.

(5) Philosophical School There is a division called Praxiology in the Polish Academy of

Science. Praxiology is an academic field where general rules are studied which relate the motivation and behavior of human beings. Gasparski [S] is a member of this division and studies the design. He studies the thought process of human beings in the design, the nature of knowledge useful for design, the relationship between the natural and the artificial, that is the designed. He is aiming at elucidating the human beings through their designing behavior. Therefore he may be categorized a philosopher.

5. DESIGN SCIENCE

As seen in the last chapter, there are many proposals that are to be usefully applied to the actual design activities, in not completely but considerably wide domains of technologies. There are various schools, where the respective aspects of design are emphasized and therefore. at least under the limitation of domains. the applicability to the particular domains being highly expected.

On the contrary, the answerers of the questionnaire who are the users of methodologies were rather negative for using those methodologies. Peter [A] proposed a home-made methodology. Pruvot [A] mentioned his skepticism to the design theoreticians and artificial intelligence researchers. German Colleague, Dahl [A] and Weck [A], mentioned more moderately to reform and combine the design methodologies proposed by different authors. or maybe schools.

In order to improve this situation and narrow the gap of the conceptions between the maker and the user of design methodologies, i t might be necessary to explore some other approaches than establishing a method by collecting and organizing what the maker had experienced in her professional career.

As many Colleagues emphasized, the cooperation of the users and makers of the methodologies will be appreciated. Then a question arises: by what way? For effective cooperations, it is crucial that both sides have a common language. Let us investigate some examples.

(1) Designers and Design Theoreticians Usually, a so-called design theoretician has the considerably

long experience of the design practice in a particular technological field and she abstracts a theory from her all experiences. Therefore, even if she insists the general applicability to any technological field of her theory, the theory usually inherits the nature of original field and less useful in other fields. For instance, the design methodologies developed by architects are not satisfactorily useful to machine designers. On the contrary, a design methodology developed by a machine designer is, needless to say, useful for other machine designers. But in this case, the universality of the methodology can not be proved.

(2) Designers and Information-processing engineers It seems difficult for the information-processing engineers to

understand the mechanical engineering. Therefore, it has been pointed out that the CAD, usually developed by the information- processing engineers, is functionally limited due to too much simplification of mechanical elements. Or, the automatization of the design process is backward in the mechanical engineering when compared with other engineering fields such as the electrical circuit design and the architectural design. This fact may be attributed to that both the design object and the design process of the mechanical engineering are more difficult for them to understand than in the electrical and architectural. The reason of the difficulty is the lack of efficient languages for explaining the mechanical engineering, or in other words the lack of a good common language between the information-processing engineers and the mechanical engineers.

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The language barriers that obstruct the efficient cooperations seems to be too much inheritance of particular fields, of the makers on some occasion and of the users of another occasion.

If our target is to establish a universal methodology of design without deteriorating the practical usefulness, the above discussion may lead to a conclusion that we need accomplish a methodology that is not inherited by any field and still keeping the usefulness.

fTransformatio;;\

be introduced, under the condition that the possibility of confirmation or refutation of the theories by experiments is preserved.

6.1 Experimental Design Theory [I41

6.1.1 Method Effectiveness

When considering the CAD systems that aid designers in

Evaluation

Information Processing Exeeutabili@ U

Fie.5 Desim P r o w s Model Let us look at Fig.5. When we observe the design process

conducted by designers, we may obtain some records of the process. An arrangement of the records will be a text that guides novices, being a design methodology. But this is only useful for the domain and not universal.

Secondly, if we succeed to apply some models such as control- theoretic, artificial-intelligence-like etc., then we shall improve the efficiency of the methodology because we can generate a useful method for the particular design by manipulating the models that are more general than the above-mentioned methodology as a faithful record of the designing process.

However, these models are borrowed things after all, from other fields such as control, and therefore obtained through more or less arbitrary abstracting procedures. Thus, they can not be sufficient and, of course, highly inherited by the original domains where the borrowing of the means was successfully done. Intelligent CAD constructed on the base of these methodologies are intrinsically limited by the inheritance.

The final target for the present purpose must be constructing a general theory of design. The theory should be universal, that is, need hold in any field of technology. Of necessity, such theory will be very abstract, being free of the contamination from some specific fields. Then a question arises: How can an abstract theory be useful for practical designing?

It can, if the theory has such potential that it generates domain- specific methods practically applicable to the particular domains. A theory. by its definition, must carry such an attribute. Newton’s theory covers all phenomena of the moving bodies. Design theory must explain all phenomena of design activity. Only the theory can be universal and efficient by its predictability that is given spontaneously owing to its consistently.

.The significance of the general design theory, for improving the design technology and fabricating the intelligent CAD, was pointed out by the present author in 1974 1121, in the occasion of a conference organized by CIRP. Since then some researches have been conducted to establish a general design theory based on the

Recently researchers of different technological fields, such as architecture, machine, electronic circuit, naval architecture, materials etc. have started to develop more or less general design theories. On the other hand, the researchers of cognitive science started to be interested in the design. One of the streams of those researches is based on the logics as its mathematical means.

As the Cartesian Pruvot rightly pointed out, those theories are still incomplete and not directly useful for practical design activities. However, we should not neglect them or we should cooperate for the further development of those theories, which might be hopefully called design science.

topology.

6. S T A T E - O F - T H E - A R T O F G E N E R A L DESIGN THEORY

In this chapter, an experimental method, that is necessary for a theory to be scientific, will be described first. There, observability of the thought process will be discussed. Secondly theories that aim at elucidating the design process systematically and consistently will

conceptual stage of design, it is how hopefully said ;hat the knowledge engineering will be usefully applied for their systems construction. If this is correct, we are required to understand correctly about the knowledge which plays important roles in the design process. The knowledge in design, however, has not been taken up as a research subject in any field, although it performs practically the most important role everywhere.

Recently, many researches have been conducted in the field of knowledge engineering and useful results were obtained about the methods to manipulate the knowledge. Typical examples are predicate calculus, semantic net. production rule and frame. They were applied to some practical problems, confirming usefulness of these methods generally, apparently, however, these methods are for manipulating the knowledge given, but they do not teach us the necessary knowledge itself, only indicating us the format.

More precise understanding is necessary about the design process, where various kind of knowledge plays different roles. For this purpose, knowledge engineering alone does not work sufficiently. Some theory, such as the general design theory, must cooperate with it.

In this section, an inductive approach of the general design theory is introduced, which gives the confirmation of theorems deduced in the axiomatic approach of the theory. In this approach, we conducted experiments from which we could obtain not only the confirmation for theorems, but also a plenty of important facts about the real process of design that have not sufficiently been deduced in the axiomatic approach.

There are different methods to investigate the thinking process by human beings experimentally. For example, after a subject of the experiment thinks about something, he or she is asked to tell the investigator about the process of thinking. We, however, had to conclude that this method has terribly low accuracy of observation. The subject often forgets essential steps of thinking. In case of thinking in design, this oblivion is dominant, suggesting the randomness of thinking in design. It is our conclusion at this moment that a dialogical method is feasible, where designers are asked to tell others what he thinks in order to process the design.

In this method, we prepare two or more subjects of experiment, asking them to design something under given specifications. The sequence of this method is shown as follows:

(1) Let two or more subjects to make a design team. (2) Ask these subjects to conduct design cooperatively by

discussing freely about the given requirement specifications.

(3) Record the discussion with a tape recorder, or if necessary record the illustrations drawn by team members with a video recorder.

(4) Analyze the records. It should be noted here that the characteristics of the

requirement has significant influence on the results of such experiments. For example, where the team is given a familiar problem, they often conclude a good result of design without discussion, hence obtaining only poor observation of designing process. Therefore we used such requirements that are

(1) Some that are as unprecedented as possible, (2) Some that do not require so much special background, and (3) Some to be finished within a few hours. In this methods, there is considerable amount of thinking which

is not uttered. But the accuracy of observation is by far better than others.

6.1.2 Examples of Experiment

The subjects of experiments were undergraduate students of engineering department. Some examples of the requirement specifications are as follows, ex.1 Design a dress in which you are comfortable under any

climate. No other conditions. ex.2 Design a apparatus by which a bedridden person can read

books easily. There are conditions (1) the person may be facing upward, (2) turning of pages must be done remotely. (3) books

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must not be stained, (4) it may be as cheap as possible, ( 5 ) as simple as possible, (6) as small and light as possible.

ex.3 Design a dozing-preventer, with conditions (1) portable and (2) it should not injure the user!

These experiments were conducted by design teams of two students respectively.

6.1.3 Extraction and Classification of Thinking

In Fig.6. an example of record is illustrated. Each utterance includes a few sentences. The sentence is sometimes used for the analysis of the requirement, and for proposals of design at others. It seems difficult to give a strict definition on the atom of thinking process from the semantical aspect. For the present purpose aiming at extracting a fundamental structure of thinking process in design, it seems enough to give two categories according to the results obtained in the axiomatic approach. These categories are the description of functions and attributes. Each are given sub- categories which will be discussed later.

Subject A: For reading of books. letters must exist in his sight. B: The problem is how to display them. It is not neccessarily required

to display the book itself A: Oh, yes. B: Well, let us think of a machine, which sees the letters in the W.

It reads them by panem-regcognition, transform them into voices.

A Ok. But the motion must 'be three dimentional. B: It seems easy. We must find out some mechanism that moves

I

smoothly.

(1) Description of function The major portion of the utterance was found for the description of function. This has such form as (display letters), (fix the book), (isolate the room from outer atmosphere), function is generally described only in linguistic way. The standard form of the description can be written as follows. (transform an object which is in a state into a different state by giving some process) The original requirement given to the design teams have fundamentally this form. More simply, the description of function has the form as (verb)+(noun), by verb indicating the content of the process and by noun indicating the object to be processed.

In the experiments, the next major portion of the utterance is the description of attribute of the object being discussed. Examples are (it moves three-dimensionally), (the pressure is below one atmosphere), and (it can stay in 18OC for long time). These expressions seem to describe the attributes of certain object. Its general form is (has some intrinsic characters), Theoretically, the solution of design can be described by the attributes of an object, that is the solution. And the characters involved in the attributive description must be by physically-well-defined words. There are, however, often described by names. For instance, (it is like steel) instead of (it has specific weight of 7g/cm3, Young's modulus of 2.1*10'kg/mmZ, ...). These are substantially the same, but the efficiency of representing the characters of solution.

(2) Description of attribute

(3) Subcategories of both descriptions I I Known I Unknown 1 I - . . ..

(to be r e f e d ) (to be designed) Subject Object Subject Object

(to process) (to be processed) (to process) (to be processed)

Cat- . . According to the general design theory, the design is an identity mapping from functional space to attributive space. In order to elaborate this mapping through the present experiment, we introduce a little finer categorization in both functional and attributive descriptions. Designers often bring up a known machine as reference or a tentative solution. And, of course, they propose a new, that is unknown, machine as a solution. Therefore, we lay down two subcategories: known f , m. and unknown F, M. Each subcategory is divided into two, that is subjective and objective. The subjective is the machine to be

designed, and the objective is something which is processed by the machine to be designed. Thus we provide eight subcategories. They are shown in Fig.7.

6.1.4 Transition between Units - Process Dynamics

On the basis the subcategories introduced above, the experimentally observed designing process can be represented as a sequence of transition between the thinking unit.. corresponding to the subcategories. The analysis of the experimental results revealed some interesting facts as follows.

(1) Fundamental transition The general trends found in the transitions are between the function and the attribute. Fig.8 shows a summary of the first part of discussion recorded in the first experiment. It is easily seen that the transition are basically between functions and attributes. The design progresses stepwise by these transitions into the final solution. In this example, a member of the design team offered the space suit as a tentative solution of the given requirement, that is all-weather dress. This is a transition from function to attribute which is described by a name of entity in this case. Next, tentative solution is analyzed for evolution by detecting its functions. This analyzing process is categorized into the transition from attribute to function. In all experiments, we could epitomize the whole designing process as a chain of alternations of transition in both ways.

[Functional Description] [Amibutive Description] All-weather dress.-

people nccd fresh air.- Space suit.

-Space suit with louver.

S n s m l l air conditioner. Approriatcncss in hot place?

Too heavy.- ! \Air conditioner with latent heat of ! e v a T t i o n . . . . . Fig.8 T r m o n s bet ween Th-

(2) Detailed classification of transitions The records of designer's utterances were investigated, dividing them into atoms each of which was assigned one of the eight subcategories given in Fig. 7. It is easily understood that the records are equivalent to Markovian processes where the transitions between these subcategories are the steps of the process, therrfore, the whole process can be represented by a Markovian transition probability matrix, a result of the second experiment being shown in Fig9 as an example. In this figure, each transition probability is accompanied with the total number of occurrence and the absolute probability of occurrence of the particuiar transition.

To

Upper: number of obsavcd uansition. total number 5% Mi& its ratio Lower: transition probability

Fie9 W o . . .. vian Tr- Probabrlitv Matrix

This matrix indicates the characteristics of the designing process

observed. For example, in case that the designers are skilled experts in the particular field of requirement, the proposal of a tentative solution which is feasible will appear soon after the requirement is presented, without sundry considerations about the requirement. Therefore, the probability for transition F-tM will dominate in the matrix. But the matrix in Fig. 9 shows that it is not the case in the present experiment. Let us remember that the subjects are undergraduate students.

There can be 64 kinds of transitions theoretically according to the above mentioned categorization of thinking unit. Some of them, however, are not observed practically, and in fact they are not important from the viewpoint of design process. We can select some transitions which are observed frequently. They are shown as follows.

(a) Transition :Function + Attribute This is the most important transition in the design process because it advances the process toward the final solution. These are subcategories transitions actually observed: Fs+Ms (number of occurrence = 54). Fo+Ms (19). Fs-Mo (9).

(b) Transition : Attribute Function This transition occurs when designer analyses the newly proposed solution or the known machine referred, in order to detect their functions to the compared with the requirement functions. They are subcategorical transitions observed: Ms+Fs (1 13), Mo+Fs (16). Ms+fs (1 I ) , ms+fs ( I I ) .

This transition includes two different aspects. One is the detailing process of requirements and another is that where two functions are compared : functions of newly proposed machine and of given requirement for instance. Subcategorical transitions are Fs+Fs (89). Fs-tFo (34). Fo+Fs (16) and

(c) Transition : Function + Function

fs+Fs (10).

(d) Transition : Attribute + Attribute This type of transition was popularly observed in the experiments. This usually follows the transition Fs+Ms. After new proposal of solution is presented, the discussion and elaboration about the presented proposal continue for a while. The process generates this type of transition. Subcategorical transitions are Ms-tMs (37) and ms+Ms ( I 1 ).

6.2 Topological Design Theory

6.2.1 Principal Results of General Design Theory

The general design theory presented elsewhere [ 131 is based on a topological model of human intelligence. It starts with some definitions. D1. The entity set is a set which includes all entities in it as

elements. D2. The item of attribute and its value. Attribute of entity are the

properties; physical, mechanical, geometrical etc., which can be observed by scientific means. An entity has respective values for attribute items.

D3. When an entity is exposed to a circumstance, a behavior of the entity is observed which is correspondent to the circumstance. This behavior is called visible function . Different behaviors are observed for different circumstances.

D4. Concept of entity is a concept which one has formed according to the actual experience of an entity.

D5. Abstract concept is derived by the classification of concepts of entity according to the meaning or the value of entities. There are some kinds of abstract concept which correspond to the characteristics of meaning. l l e y are concept of attribute, concept of function etc.

By using these defmitions, we established the following axioms which are guaranteed by intuition. A l . Any entity can be recognized or described by the attributes.

A2. The entity set and the entity-concept set have one-to-one

A3. The abstract-concept set is a topology of the entity-concept

(Axiom of recognition)

correspondence. (Axiom of correspondence)

set. (Axiom of operation)

From these axioms, we can deduce theorems which mention about designer's designing process. Some pertinent theorems will

be shown here. It must be noted that the mathematical operations are done under the assumption that the concept space is continuous, that is the space has infinite capacity of memory. It is not the case in real designers, but the designing process by real designers can be thought the approximation of the ideal process, or superman's designing process. Or, in some cases, it is interesting to investigate the deviation of real designer from the superman. Concerning superman's knowledge, we obtain the following theorems.

n

of Th- T 1. The design requirement is the intersection of abstract concept

in functional space. T2. The design requirement is a filter. T3. The design solution is the intersection of abstract concept in

attribute space. T4. If design is possible, the identity mapping from the attribute

space (S,fl) to the function space (S,T') is continuous. These theorems are schematically shown in Fig.10. T1 says that

the design requirement is described as

T2 insists that the above equation should not be null set, otherwise it happens that no solution is possible which is logically feasible. T3 means that the solution is an element of the entity set S which is included in TIR. Then, because the solution must be described in terms of attribute, T 4 becomes important. Unless T4 holds, it is not possible to designate a region of entity set S which necessarily includes the solution. So, the design solution is

T;=T:~T:~,

$=fn<nf

where TlR3f l s . T4 insists

N. T;=Ti,n#%n ... nT:

When these theorems hold, it is guaranteed that the design requirement in the functional space has a corresponding solution in the attributive space any element of which will satisfy the requirement.

6.2.2 Designing Process

In the last section, we have shown some results of general design theory where we can discuss about human concepts important in design problems. The primary purpose of the present paper is to discuss about the microscopic steps in designing p m s s which are to be substituted by computer. So, the designing process will be modeled on the spaces mentioned in the last section. First, we have the following theorem. T5. By detailing the design requirements, we obtain the sequence

of entity concepts which converges into a point of entity set.

1 ConverFence into Solution This theorem is illustrated in Fig. 11. In the case of superman,

this process will be realized without difficulty. Because of its perfectness of the memory space and rapidness of operation, the convergence will achieved easily. Then the superman will analyze it, in other words, find out the necessary information for manufacturing it among the neighborhood system in the attributive space. We can say that the superman designs transforming the functional description of the requirement into the attributive description which is the solution through the medium of the entity concept. This process requires perfecmess of memory structure.

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In case of real designers, such simple process usually results in a failure because of the imperfections in memory structure [13]. Further discussion is found elsewhere [ I 51.

6.3 Design Process Theory

If we introduce an assumption, say a definition, that the concept in the axiomatic theory corresponds to the utterance in the experimental theory, then we may compare the both theories or the axiomatic theory can be confirmed by the experiments. Thus we may say that the design theory is qualified to be scientific.

By using axiomatic approach, some theorems were deduced from the axioms assumed. Especially, there was a theorem which proposes several designer’s designing models that appear in different design activities. They can be subjected to confirmation by using the empirical results of experiments in the preceding section.

ween The most basic idea in the axiomatic general design theory was

the establishment of the functional space and the attributive space between which the design was defined as mapping. It is readily seen that the designing process observed in the present experiments can be modeled as trial-and-error mapping between these spaces. The sequence of transition: FO+Fl, F l + M l , M1-+M2, M2-1F2, F2+F3 is illustrated on these spaces, in Fig.12. FO-+Fl transition is the shrinkage of a functional subset that is the elaboration of original requirements. The second transition, F l + M l , is the first trial of mapping from the functional space to the attributive space. This is usually to the known machine designated ms and often redesigned to Ms, that is M2 in this figure. The mapping from M2 to F2 is a process detection the functions of proposed machine M2, revealing the failure of this first “design”, F l + M l because the result if detection, F2, is not included in the original requirement F1. Then a new mapping is planned being promoted by the gap between F1 and F2.

More detailed discussions about the confirmation were reported elsewhere 1141, [ l l ] . Here, we shall point out an important subject of the design theory to be developed. As readily seen by the above discussion, the topological theory of design well represents a structural model of the human thought on which the design is conducted. Dynamic principles of the conduct, however, are not explicitly presented. Further study has been developed on this problem, the design dynamics, and reported elsewhere [ 151. Simply, the results are that by introducing a metric system into the attributive and functional spaces, thus giving distances among the elements of both spaces, a method of mapping has been theoretically available. But we need more study in order to conduct the mapping in practice.

Recently, many researchers on the design theory and the intelligent CAD have started being interested in the application of the logics which they expect is useful for representing both the design knowledge and design dynamics [3]. In order to give a brief account of the idea of these studies, let us deal with a simple example by using a syllogistic model of design.

Once upon a time, there were some people who did not have any cups. They drank water by using their own palms. Someday, one of them invented hot coffee, which is delicious and appreciated by people. They drank hot coffee by using their palms because they had no cups. Of necessity, their hands were burnt, always brunt as they used to drink hot coffee. We can imagine that it was not comfortable.

Design started with this uncomfortableness. The design process is modeled in terms of syllogism. Normally it is described as

M a P (Axiom) S =$ M (Premise)

S 3 P (Theorem). Then, let us replace each term with the present design task as follows:

M: Something by which one can drink hot coffee without burnt. P : One can drink hot coffee without burnt. S : This thing.

More easily, we can say “We know that if we use something by which one can drink hot coffee without burnt, then we can drink hot coffee without burnt. And this thing is a member of the something. By syllogistic process, then, we conclude that we can drink hot coffee without burnt if we use this thing.” In this syllogism, the requirement of design is the Theorem. The Axiom is the design knowledge and finally the design solution is the Premise. The inference of the Premise from the Axiom and the Theorem, is called abduction. Therefore, the design in a narrow sense is the abduction.

Readers may be skeptical about this model, because this process seems a tautology. The design must be anything but a tautology. But this is not a tautology because the Axiom insists that there should be something that fulfills the requirement. This thing is the solution.

We understand this syllogism represents only a part of design. We must go further to find out this thing as a concrete and real entity. We need more metaknowledge (Axioms) that is essential for the inference in the design. They are as follows: M1) Any functionality can be represented by a composifion of

some numbers of sub-functionalities, M2) Any entity can be represented by an inlegrotion of some

numbers of elements (sub-entities). M3) The functionality of an entity is a composition of the

respective functionalities of elements with which the entity is made through integration.

By using these pieces of meta knowledge, we can process the design. In this case, we use A (and) as the composition and u (Union) as the integration. Then,

(Drink hot coffee without burnt) = (Fix coffee A Transport the fixed coffee without burnt A Transfer coffee from the fix to mouth)

We use again the syllogism, A * Fix coffee B * Transport C Transfer a * A b *B c *c a *Fix coffee b *Transport c *Transfer

Where A, B, C are the abstract concepts and a, b, c are entities. Finally we get a solution S,

S = a u b u c.

7. THANKS

The author would like to mention great thanks for the kind cooperation of CIRP Colleagues, especially DN Members. Hopefully, I expect that readers have got some idea of design theory/philosophy by this simple paper. Design might be an everlasting subject for us. But at the same time, the design has become an urgent task for us to understand deeply and sufficiently, because we, manufacturing engineers, are highly responsible to design and manufacture artifacts that are good for people from the viewpoints of society, environment, resource, energy, psychology, economy and others.

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