oxman 1997 design by representation

8/12/2019 Oxman 1997 Design by Representation

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D esign by r e r epr esen tat ion : a m odelo f visu a l r eason i n g n designR i v k a O x m a n , F a c u l t y o f A r c h i t e c t u r e a n d T o w n P l a n n i n g , T e c h n i o n ,Ha ifa , I s rae lThe conception o f design as a sequential p roces s o f descript ion an d re-descript ion in the develop men t of designs is presented. Re-representational theory RR H ) is introduced an d the cognitivemechanisms wh ich enable re-representation in design are explicated. Atheory o f re-representat ion an d mult iple representat ions in design isproposed. The concept of adaptat ion develop ed in CB R is exploi ted tofor m aliz e transformations in the re-representation p rocess. An empiricalresearch was constructed to study the cognitive abilities which underliethe creative pheno me na o f re-representation in design adaptat ion. Onthe basis o f the f inding s o f the experiment , a m odel o f design re-representation is develo ped and presented. The main concepts o f themodel , m ult iple representat ion an d re-representation, are show n topro vide a powe rful basis fo r the understanding of creative beha vior indesign. 199 7 Elsevier Science Ltd.Keyword s: draw ings, re-representation, creativity, design precedents,des ign process

1 SchOn, D A The ReflectivePracti t ioner: How r o f e s s i o n a l sThink in Action I=~sic Books,New York 1983)

Lawso n B How DesignersThink The A rchi te ~ ra l PressLondon 1980)3 A k i n , O Psychology o f Archi-tectural Design P~on, London1988)

ELSEVIER

e de s ign ske t c h c a n be c ons ide r e d a s t he ba s i s o f a v i sua l a ndm e n ta l t r a nsa c t ion be tw e e n the de s igne r a nd the r e p r e se n t a t i on ,w h ic h e voke s a d i s c r e t e g r a ph ic a l r e sponse . A c c o r d ing to S c h r n ,

t he de s igne r is e nga ge d in g r a ph ic a l c onve r sa t i on w i th t he de s ign t o ra c c o r d ing to La w son , t he de s igne r ha s a c onve r sa t i on w i th t he d r a w ing 2.I t i s t he se t r a nsa c t ions w i th t he e x t e r na l r e p r e se n t a t i on w h ic h i l l um ina t ethe v i sua l - m e n ta l p r oc e s se s o f de s igne r s . W he r e g r a ph ic m e d ia suc h a sde s ign ske t c he s a r e t he m e d ium w he r e by the de s ign i s e vo lve d , de s ignm o ve s a r e a s e ri e s o f a c t i ons o f the de s igne r w h ic h re su l t i n tr a ns f o r m -a t ions o f a re p r e se n t a t ion 2 ,3 . The t e r m m ov e i s f r e que n t ly e m p loye d inc on te m p or a r y de s ign r e se a r c h to de sc r ibe t he d i s c r e te i nc r e m e n t s o f c ha ng ein t he e vo lu t ion o f a de s ign .Th i s e luc ida te s o ne o f the d i s t i nc t i ve c ha r a c te r i s ti c s o f the g r a ph ic a l de s ignp r oc e s s , pa r t i c u l a r ly t he p r oc e s s o f c onc e p tu a l de s ign , na m e ly , i t s de ve lop -

0142-694X/97 17.00 esign Studies 18 (1997) 329-347 PII: S0142-694X(97)00005-7 1997 Elsevier Science Lid All rights reserved Printed in Great Britain

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4 0 x m a n , R M T h e r e f l e c t i v ee y e : v i s u a l r e a s o n i n g i n d e s i g nin A Koutamenls, H T l m m e r -m a n e n d I V e r m e u l e n ( e d s ) Visua/ data bases in archi tectureAverbury, Aldershot, U.K. (1995)pp 89-112.5 Arnhelm, R Visual ThinkingU n i v e r s i t y of California Press,Berkeley and Los Angeles1 9 6 9 )

m e n t t h ro u g h a s e q u e n c e o f p r o g r e s s i v e s t a g e s o v e r ti m e . T h e s e q u e n c e o fs k e t c h e s c a n a c t a s a r e c o r d o f r e a s o n i n g p r o c e s s e s w h i c h c a n b e i n f e r r e df r o m a transition o f states f r o m o n e r e p r e s e n t a t i o n t o a s u b s e q u e n t r e p -r e s e n t a t i o n .T y p i c a l p r o c e s s e s c a n b e i n t e r p r e t e d a n d c a t e g o r i z e d a s c l a s s e s a n d t y p e so f m o d i f i c a t i o n o f t h e r e p r e s e n t a t i o n 4. A c c o r d i n g t o A r n h e i m 5 , c o g n i t i v eo p e r a t i o n s i n p e r c e p t i o n i n d e s i g n i n c l u d e d i s t i n g u i s h i n g s t r u c t u r a l r e l a t i o n -s h i p s o f th e i m a g e s i n t h e d e s i g n r e p r e s e n t a t io n . T h i s i n c l u d e s t h e i n t e r p re t -a t i o n a n d c o n c e p t i o n o f s u c h s t r u c t u r es o f re l a t i o n s h ip s ( p r o t o t y p e s ) . S p a -t i a l g e s t a l t a n d t h e s t r u c t u r a l q u a l i t i e s i n c o n f i g u r a t i o n s a r e e x t r e m e l ys i g n if i c a n t in c o n c e p t u a l d e s i g n . T h e s t r u c tu r i n g a n d r e s t r u c t u r in g o f s h a p e sw h i c h m a y b e o b s e r v a b l e i n s e q u e n c e s o f s k e t c h d e s ig n r e p r e s e n t a t i o n se v i d e n c e t h e c o g n i t i v e a b i l i t ie s o f t h e d e s i g n e r s u c h a s t h e a b i l i t y t oe v o k e p r o t o t y p e s .T h e w a y c r e a t i v e d e s i g n e r s f i t a n d a d a p t g r a p h i c a l r e p r e s e n t a t i o n s t h r o u g hd r a w i n g a n d r e d r a w i n g i s o n e o f t h e l e a s t u n d e r s t o o d p h e n o m e n a i n d e s i g n .D e s p i t e c u r r e n t w o r k i n u n d e r s t a n d i n g g r a p h i c a l r e a s o n i n g i n d e s i g n , t h ew a y p e r c e p t u a l a n d c o n c e p t u a l m e c h a n i s m s o p e r a te i n d e s ig n d r a w i n g a r es t i l l u n f o r m u l a t e d . T h e w a y k n o w l e d g e i s e m p l o y e d a n d s e q u e n t i a l c l a r i f i -c a t i o n a n d c o n c e p t u a l e n r i c h m e n t a r e s u p p o r t e d i n d e s i g n r e q u i r e s s t u d y ,u n d e r s t a n d i n g a n d f o r m a l i z a t i o n . T h e s e a r e a m o n g t h e o b j e c t i v e s o f o u rw o r k .F o r m a l i z i n g t h e p r o c e d u r a l a s p e c t s o f d e s i g n m o v e s m a y c o n t r i b u t e t o o u ra b i l it y t o m o d e l v i s u a l r e a s o n i n g i n d e s i g n . T h i s d e s c r i p t i o n - r e - d e s c r i p t i o np r o c e s s i s o n e w a y i n w h i c h d e s i g n e r s c o g n i t i v e l y e x p l o i t g r a p h i c a l r e p -r e s e n t a t i o n s 4 a n d i s , th e r e f o r e , r e l e v a n t t o t h e m o d e l i n g o f d e s i g n . S e q u e n -t i a l m o d i f i c a t i o n i n d e s i g n d r a w i n g i s a m e d i u m t h r o u g h w h i c h d e s i g np r o c e s s e s o p e r a t e a n d a r e m a d e m a n i f e s t .

owards a re rep resen ta t ion m ode l o f v i sualreasoning in des ign drawingsI n th i s p a p e r , w e p r o p o s e a m o d e l o f th e c o g n i t i v e m e c h a n i s m s a n d a b i l i ti e sw h i c h u n d e r l i e a n d e n a b l e s e q u e n t i a l s t a t e s o f g r a p h i c a l r e - r e p r e s e n t a t i o ni n d e s i g n . W i t h r e f e r e n c e t o c e r t a i n r e l e v a n t p s y c h o l o g i c a l t h e o r i e s c i t e db e l o w , w e r e f e r t o t h i s m o d e l a s a re representational mo del o f designreasoning. The m o d e l i n g i s f o u n d e d u p o n a n e m p i r i c a l s t u d y o f d e s i g n e rsb e h a v i o r i n t h e g r a p h i c a l a d a p t a t i o n o f a d e s i g n s o l u t i o n . T h e o b j e c t i v e o ft h e e x p e r i m e n t w a s t o s t u d y t h e w a y d e s i g n e r s m a n i p u l a t e g r a p h i c a l s y m -b o l s i n d e s ig n d r a w i n g s , a n d t o i d e n t i f y th e k n o w l e d g e a n d c o g n i t i v e c a p a -b i l i t y r e q u i r e d t o e n a b l e r e - d e s c r i p t i o n i n d e s i g n .

3 3 0 D e s i g n S t u d i e s V o l 1 8 N o 4 O c t o b e r 1 9 9 7


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W e h a v e m o d e l e d t h e k n o w l e d g e e m p l o y e d i n v i s u a l r e a s o n in g i n t h e i n te r -a c t i o n o f g r a p h i c d e s i g n p r e s e n t a t i o n . I t i s t h e s e t r a n s a c t i o n s i n a g r a p h i c a lm e d i u m w h i c h w e a t t e m p t t o s t u d y , t o m o d e l a n d t o f o r m a l i z e . A s w ed e m o n s t r a t e t h r o u g h p s y c h o l o g i c a l s t u d i e s , th i s l e v e l o f k n o w l e d g e u n d e r -l i e s t h e c o g n i t i v e a b i l i t y f o r s t ru c t u r i n g , o r g e n e r a l i z a t i o n , o f t h e r e p r e s e n -t a t i o n . W e h a v e p r o p o s e d a r e - r e p r e s e n t a t i o n a l m o d e l w h i c h a t t e m p t s t oi d e n t i f y a n d f o r m a l i z e t h e l e v e l o f k n o w l e d g e w h i c h i s r e q u i re d f o r m a k i n gt r a n s f o r m a t i o n s o f r e - re p r e s e n t a t i o n i n t h e i n t e r a c t i o n w i t h t h e g r a p h i c a lm e d i u m . A s a re s u l t, w e i d e n t i f y a n d c h a r a c t e r i z e t h e t r a n s f o r m a t i o n a l p r o -c e s s e s i n v o l v e d i n i n c r e m e n t s o f s t a t e t r a n s a c t i o n . F u r t h e r m o r e , w e e x p l i -c a t e t h e e x p l i c it s e t s o f k n o w l e d g e s t r u c t u re s w h i c h e n a b l e t h e m t o o c c u r.T h i s e x p e r i m e n t t h r o w s l i g h t o n t h e d i f f e r e n c e s i n t h e c o g n i t i v e a b i l i t y o fi n d i v i d u a l d e s i g n e rs . I t a l s o p r o v i d e s i m p o r t a n t i n s i g ht s o n k n o w l e d g e a n dr e - r e p r e s e n t a t i o n a s p h e n o m e n a o f c r e a t i v it y .T h i s w o r k e m p h a s i z e s t h e f o l l o w i n g p o i n t s :(1 ) conceptual structures of knowledg e in visual reasoning in designG r a p h i c a l r e a s o n i n g i n d e s i g n i s v i e w e d h e r e a s a t r a n s a c t i o n b e t w e e nc o n c e p t u a l k n o w l e d g e s t r u c t u r e s a n d d e s i g n r e p r e s e n t a t i o n t h r o u g h a v i s u a lr e p r e s e n t a t i o n a l m e d i u m ;(2) a re representation theory fo r visu al reasoning in designB a s e d u p o n e m p i r i c a l r e s e a r c h , a n d i n o r d e r t o e x p l a i n t h e c o g n i t i v e a b i l i -t i e s e n a b l i n g t h e s e q u e n t i a l e v o l u t i o n o f g r a p h i c a l r e p r e s e n t a ti o n s , w e p r o -p o s e a r e - r e p r e s e n t a t i o n a l m o d e l o f v i s u a l r e a s o n i n g i n d e s i g n ;(3 ) a re representational m od el in design ad aptationT h i s m o d e l i s h i g h l y r e l e v a n t t o c o g n i t i v e a n d c o m p u t a t i o n a l a p p r o a c h e st o d e s i g n s u c h a s C a s e - B a s e d D e s i g n ~5. O n e o f t h e p r i o r i t y r e s e a r c h i s s u e si n C B D i s t h e fo r m u l a t i o n o f a p p r o a c h e s a n d p r o c e s s e s to t h e a d a p t a t i o no f d e s i g n s , o r t h e m o d i f i c a t i o n o f p a s t d e s i g n r e p r e s e n t a t i o n s t o f i t a c u r r e n td e s i g n s i t u a ti o n . W i t h i n t h e c o n t e x t o f C B D , w e p r o p o s e t h e r e l e v a n c e o fo u r r e - r e p r e s e n t a t i o n a l m o d e l a s a b a s i s f o r f o r m a l i z i n g a d a p t a t i o n ;(4 ) re representational theory as a foun da tion of studies o f design crea

tivityM o d e l i n g t h e i n te r a c t i o n w i t h v i s u a l r e p r e s e n t a t io n m e d i a p o t e n t i a l l y c o n -t r i b u te s t o t h e u n d e r s t a n d i n g o f th e r e l a t i o n s h i p b e t w e e n c o n c e p t s , k n o w l -e d g e s t r u c t u r e s a n d c r e a t i v i t y i n v i s u a l r e a s o n i n g . T h e m o d e l o f re - r e p -r e s e n t a t i o n i s , t h e r e f o r e , h i g h l y r e l e v a n t t o t h e o r i e s o f c r e a t i v i t y i n d e s i g n .

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K a r r n i l o f f - S m l t h , A , C o n -straints o n r e p r e s e n t a t i o n a lc h a n g e : e v i d e n c e f r o m c h i l d r e n sd r a w i n g Cognit ion V o l 3 4 ( 1 9 9 3 )p p 5 7 - 8 3 ,7 B o d e n , M A The Creat iveMind My ths and MechanismsC o x a n d W e i m a n , L o n d o n( 1 9 9 5 )8 D a r t n a l l , T A I , c r e a t i v i t y , r e p -r e s e n t a t i o n a l r e d e s c d p t i o n ,in tent ional i ty , me ntal li fe : anem er g ing p ic t u r e Ar t i f i c ia l I n t e l l i -g e n c e a n d C r e a t i v i t y , t e c h n i c a lr e po r t, A A A I P r e s s ( 1 9 9 3 )

The theoretical relevance o f the re representationhypothesisC og n i t i ve a nd c om pu ta t i ona l r e se a r c he r s a r e c u r r e n tly de ve lop ing the o r e t i-c a l m ode l s w h ic h c a n a s s i s t i n the a na ly s i s o f s e que nc e s o f r e p r e se n t at i onsa nd in t he f o r m a l i z a t i on o f m ode l s . P a r t i c u l a r ly r e l e va n t t o ou r r e se a r c hha ve be e n the p syc ho log ic a l t he o r i e s o f re - re pre se n ta t ion w i th g r a ph ic a lr e - r e p r e se n t a t i on . I n m ode l ing r e - r e p r e se n t a t i on i n de s ign , w e ha vee xp lo i t e d the R e - R e p r e se n t a t i on H ypo the s i s ( R R H ) , a p syc ho log ic a l t he o r yo f c r e a t iv i t y6 . The R R H i s a c ogn i t i ve a pp r oa c h w h ic h e xp la in s c r e a t i v i t ya s a n a c t o f c onc e p tua l e xp lo r a t i on t h r ough r e - r e p r e se n t a ti on 6 -8 . R R Hthe o r y ha s be e n r e l e va n t t o ou r r e se a r c h in de s ign , s i nc e i t p r ov ide s ap l a u si b le m o d e l o f th e w a y i n w h i c h h u m a n b e i n g s e x p l o re n e w m o d i f i-c a t i ons t h r ough t he e x t erna l i za t ion o f k now le dge s t ruc tu re s i n r e pre se n -tations.

The hum a n c a pa b i l i t y t o t r a ns f o r m know le dge in to r e p r e se n t a t iona l s t r uc -tu r e s unde r l ie s t he a b i l it y t o m a k e nove l m od i f i c a t i ons a nd c ha nge s i nthose r e p r e se n t a t i ons . R e se a r c he r s i n R R H the o r y ha ve de m ons t r a t e d t ha tr e p r e se n t a ti ons o f d r a w ings w h ic h a r e p r oc e du r a l a r e no t f l e x ib l e f o r i nnov -a t ive m a n ipu la t i ons unt i l they are turned in to expl ic i t dec larat ive re - rep-re se n ta t iona l f o rm . K a r m i l lo f f - S m i th 6 de m ons t r a t e s t h is c ogn i t i ve p r oc e s sb y t h e e x a m p l e o f c h i l d r e n s c o g n i t i v e c a p a b il i ty i n d r a w i n g i n t h e f u n n y -m a n p i c tu r e s s tud y . R e - r e p r e se n t a t ion o f a f o r m i s pos s ib l e on ly a f t e r theunde r ly ing r e p r e se n t a t iona l s t r uc tu r e o f t ha t f o r m i s e x t e r na l iz e d a n d m a dee xp l i c i t i n t he d ra w ing . I n t he c a se o f t he f un ny - m a n e xpe r im e n t s , a ne x te r na li z a t ion o f t he m a n - bo dy - sc he m a is p r er e qu i s it e t o t he d i s to r ti onso f th e s c h e m a w h i c h a r e f u n n y - m e n . I n th e d e v e l o p m e n t o f e xp l i ci t r ep -r e se n t a t i ons o f f o r m , hum a ns a r e a b l e t o t r a ns f o r m im p l i c i t know le dge toe xp l i c i t r e p r e se n t a t i ona l s t r uc tu r e . Th i s a ppe a r s t o e na b le nove l ty t h r oughm od i f i c a t i on a nd c ha nge w h ic h t r a nsc e nd , c on t r a d i c t , o r de pa r t f r om thegener ic representa t ion .W e w i l l de m ons t r a t e t he d i r e c t r e l e va nc e o f t he se f i nd ings t o de sign . R e -r e p r e se n t a t i on p r ov ide s a c ha ng ing pa t t e r n i n t he g r a ph ic a l m e d ium . I t i st h is pa t t e r n w h ic h i s e xp l i c a t e d i n ou r r e se a r c h . I f w e a r e t o m ode l de s igna s a p r oc e s s o f r e - r e p r e se n t a t i on , w e re qu i re t he ab i l i t y t o m ode l de s ignthrough an d re la t ive to i t s dec lar at ive abs trac t ions . F o l l o w i n g K a r m i l l o ff -S m i th , w e a s sum e tha t the p r oc e s s o f t r a ns f o r m ing g r a ph ic a l r e p r e se n -t a t ions c a n be sup po r t e d on ly a c c o r d ing to t he de c la ra t i v e k no w le d ge s t ruc -tu re s o f de s ign r e pre se n ta t ion . In des ign , these representa t iona l s t ruc turesa r e f r e que n t ly dom a in spe c i f i c . A n e xa m ple w ou ld be t he a bs t r a c t f o r m a ls t r uc tu r e o f a pa r t i c u l a r de s ign . Th i s f o r m a l s t r uc tu r e m us t f i r s t be m a dee xp l i c i t i n o r de r t ha t spe c i fi c r e- r e p r e se n ta t i ona l ope r a t i ons c a n be a c h i e ve d

332 D e s ign S tud ie s V o l 18 N o 4 O c to be r 1997


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9 Simon, H Keyr~ote Lecture,AID 92 F i r s t I n t e r n a t i o n a l Con-ference a t a r n e g i e Mellon Uni-versity, Pit tsburgh, Pennsyl-vania, USA (1992)

on tha t s t ruc ture . Tha t i s , in orde r to re formula te a des ign representa t ion ,a n unde r s t a nd ing o f i ts s t r uc tu ra l c on te n t i n t e r m s o f t he unde r ly ing s c he m am us t be e x t e rna l i z ed . O n e o f t he c on t r ibu t ions o f ou r r e se a r c h ha s be e n tode m ons t r a t e t he cognitive a bil i ty o f the huma n design er to recognize an dexternalize the underlying schem a an d structural con tent of designs a n dthe n to wo rk relative to the declarative know ledge wh ich has been exter-nalized. D e s ign c r e a t iv i t y m a y b e s e e n in t h i s s e nse a s the a b i l i ty t o i nnov -a t ive ly r e -r e p r e se n t t he s c he m a o r t he pa r t i c u l a r s t r uc tu r a l c on te n t o f t heexte rna l ized representa t ion .I n t he m e d ium o f s e que n t i al ske t c h ing w e c a n obse r ve t he a b i l it ie s e na b l ingchange in a representat ional pattern which is supported by Knowledgestructures. D o the r e e x i s t dom ain speci fic kn owled ge structures? A c c o r d i n gto S im on 9 , d r a w ings a r e e m p loy e d f o r t he e x t e rna l i z a ti on a n d the ho ld ingo f the va r ious de s ign r e p re se n t a t ions w h ic h a l low the de s igne r t o r e a so nw i th t he de s ign . O nc e e x t e r na l i z e d w i th in t he r e p r e se n t a t i on , t he de s igne rc a n f oc us u pon a spe c t s o f t he r e p r ese n t a t i on a s a pa r t o f t he de s ign p r ob -l e m . F o r e xa m ple , m e a su r e , o r spa t i a l o r de r , a r e know le dge s t r uc tu r e s i np l a n de ve lopm e n t i n a r c h i t e c tu r e . Ea c h know le dge s t r uc tu r e m a y a l so bea s soc i a t e d w i th i t s ow n r e p r e se n t a t i ona l m e d ium . A s w e ha ve obse r ve d inou r e xpe r im e n t s i n a r c h i t e c tu r e , f o r m a l a nd c om pos i t i ona l know le dge suc ha s m odu la t i on c a n be a c t i va t e d by m a k ing e xp l i c i t a g r id sy s t e m in t heg r a ph ic r e p r e se n t a t i on , a nd the n m od i f y ing the r e p r e se n t a t i on a c c o r d ing tothe e xp l i c i t o r de r ing s c he m a . O ur r e se a r c h ha s i de n t i f i e d suc h unde r ly ingdom a in spe c i f i c s c he m a a nd kn ow le dge s t r uctu r e s, a nd the i r r o l e in de s ign .A f u r the r c on t r ibu t ion o f t he r e se a r c h ha s be e n to de m ons t r a t e t he s ign i f i -c a nc e i n de s ign o f the c on c e p t o f m u l t i p l e r e p re se n t a ti ons . I n de s ign asingle representat ion generally has embe dded various un derlying m ult iplerepresentational structures. F or e xa m ple , va r ious unde r ly ing o r de r ingm e d ia suc h a s g r id s o r z ona l s t r uc tu r e s , o r f unc t iona l o r de r s a nd r e l a t i on -sh ip s a r e f r e que n t ly im p l i c i t l y p r e se n t i n de s ign r e p r e se n t a t i ons~ L F r omour r e se a r ch , the huma n designer appears to be capable o f exploi ting sim-ultaneously these various underlying representational structures and o fmit igating between them.Thi s d i f f e r s f r om the t r a d i t i ona l R R H m ode l i n p r opos ing tha t mult iplerepresentational structures are implicit in design representations. Th ede s igne r m a y e l e c t t o m a ke e xp l i c i t t he va r ious im p l i e d s c he m a a s t hede s ign e vo lve s . Thu s , i n de s ign , t he c onc e p t o f m u l t i p l e r e p re se n t a t i on ha sa un ique s ign i f i c a nc e . I n a ny de s ign dom a in , t he r e p r oba b ly e x i s t m u l t i p l eunde r ly ing r e p r e se n t a t i ona l s t r uc tu r e s w h ic h m a y , i n f a c t , be i nhe r e n t i nc l a s se s o f de s ign p r ob le m s . W ha t i s s i gn i f i c a n t i n ou r r e se a r c h i s t he

D e s ig n by r e - r e p re se n t a t i on 333


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1 Kolodner, d L C a s e b a s e dReasoning Morgan Kau f mann1994)11 Hlnrlhs, T R ProblemSolving n Open Worlds A C a s eStudy in Design Erlbaurn,Northvale, NJ 1991)

de m ons t r a t i on t ha t designers possess the cogni t ive abi l i ty to recognizeexpl icate and m odi fy these st ruc tures and to deal wi th these various rep-resentations simultaneously.

The methodological relevance o f the concept o fadaptation in Case Based ReasoningT ho ugh d ive r se m o de l s o f de s ign r el a t e t o t he de ve lopm e n ta l p r oc e s se s ,t he w a y de s ign know le dge i s s t r uc tu r e d a nd e m p loye d in suc h p r oc e s se si s , a s ye t , poo r ly f o r m u la t e d . T he r e l a t e d r e se a r c h a r e a o f computat ionalmodels of des ign cogni t ion pr ov ide s c e r t a in r e l e va n t c onc e p t s . O ne o f theob je c t ive s o f th i s f i e ld i s t o bu i ld t he t he o r e t i c a l f ound a t ions o f de s ignc o g n i t io n t h r o u g h c o m p u t a t i o n a l m o d e l i n g o f d e s i g n p r o c e s s e s a n d r e a s o n -ing . W o r k in t he f i eld ge ne r a l l y e xp lo it s t he o r e ti c a l, e xp e r im e n ta l a nd c om -pu ta t i ona l r e se a r c h . W or k in C a se - B a se d R e a so n ing 1 a nd i ts a pp l i c a ti onto de s ign i s d i r e c t ly r e l e va n t t o t he f o r m u la t ion o f de ve lopm e n ta l p r oc e s se sin de s ign . I n t he C B R v ie w , a da p ta t i on i s e m p loye d a s a m e a ns o f f i t t i nga n o ld so lu t ion t o a ne w one , o r e vo lv ing a ne w de s ign by m od i f y ing a ne x i s t ing so lu t ion r e p re se n t a ti on . I n t h is w or k , t he c on c e p t o f a da p ta t i onde ve lope d in C B R i s e xp lo i t e d t o f o r m a l i z e t r a ns f o r m a t ions i n t he r e - r e p -resenta t ion process .T he p r oc e s s o f a da p ta t i on i nvo lve s t he r e - u se t h r ough m od i f i c a t i on( a da p ta t i on ) o f the p r io r e x i s t ing r e p r e se n t a t i ona l c on te n t o f a de s ign so l -u t i on . R e se a r c h on case adaptat ion in des ign 11 prov ides a pe r sp ec t ive inthe s tudy a nd the m ode l ing o f c ogn i t i ve s e que nc e s i n t he m od i f i c a t i on o fc a se r e p r ese n t a ti ons . W e e m p loy the t e r m , de s ign a da p ta t i on , i n t he f o l l ow -ing e xpe r im e n t de sc r ip t ion i n o r de r t o d i s t ingu i sh a nd ide n t i f y the methodo-log ic a l c on te n t o f t he re qu i si te k now le dge and forma l i ze d s t e ps o f r e ason-ing in a mo del o f gra phica l re-representation. I n ou r r e se a r c h w e e xp lo i tc e r t a in c onc e p t s de r ive d f r om a da p ta t i on r e se a r c h in C B R in o r de r t o f o r -m a l ly m ode l t he s e que n t i a l t r a n s f o r m a t ions o f g r a ph ic a l r e p r e se n t a t i onsin des ign .

A formal model of re representationT he the o r e t i c a l a s sum pt ions de ve lope d in t he f i r s t pha se o f t he r e se a r c hw e r e e m p l o y e d t o c o n s t ru c t a n e m p i r ic a l s t u d y o f d e s i g n e r s b e h a v i o r i na da p t ive t a sks e m p loy ing de s ign ske t c he s a nd d r a w ings . I n t he r e se a r c hw e ha ve a t t e m p te d to e xp l i c a te t he m u l t i p l e s t r uc tu r e s o f know le dge und e r -ly ing g r a ph ic a l r e p r e se n t a t i ons a nd to de m ons t r a t e how the y suppo r t m od i -f ica t ion in des igns .T he p r opose d a pp r oa c h to a da p ta t i on i s ba se d upon the s e m ina l c onc e p to f m u l t i p le - r e p r ese n t a t ion . T he m ode l ing o f a da p ta t i on a s a p r oc e s s o f



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r e - r e p r e s e n t a t i o n w i t h i n t h e f r a m e w o r k o f t h i s c o n c e p t f o c u s e d o n a d e s i g nt a s k o f t h e a c h i e v e m e n t o f u n i q u e d e s i g n s t h r o u g h a d a p t i v e p r o c e s s e s . S u b -j e c t s w e r e a s k e d t o c o n s t r u c t e x p l i c it r e p r e s e n t a t io n a l s t r u c tu r e s i m p l i c i t i na p a r t i c u l a r d e s i g n f o r m , i n o u r c a s e , a n a r c h i t e c t u r a l p l a n . A d a p t a t i o np r o c e s s e s i n g r a p h i c r e - r e p r e s e n t a t i o n w e r e d o c u m e n t e d t h r o u g h p r o t o c o la n a l y s i s. E m p l o y i n g t h e f i n d i n g s d e r i v e d f r o m a n a n a l y s i s o f th e p r o t o c o l s ,a g e n e r a l m o d e l o f a d a p t a t i o n o f r e p r e s e n t a t i o n s w a s d e v e l o p e d . T h er e s u l t i n g g e n e r a l m o d e l i s c o n s i d e r e d t o b e v a l i d f o r i n n o v a t i v e a n d c r e -a t i v e d e s i g n a s w e l l a s f o r r o u t i n e d e s i g n .

W e d e s c r i b e t h e e x p e r i m e n t , i t s o b j e c t i v e s , r e s e a r c h c o n s t r u c t i o n a n d f i n d -i n g s . T h e f i n d in g s w e r e s u b s e q u e n t l y e x p l o i t e d i n t h e c o n s t r u c t i o n o f ag e n e r a l r e - r e p r e s e n t a t i o n m o d e l o f d e s i g n .

4 1 bject ives and methodsT h e e x p e r i m e n t w a s c o n s t r u c t e d t o m o d e l d e s i g n a d a p t a t i o n i n th e a r c h i t e c -t u ra l d o m a i n w h i c h i s s t r o n g l y c h a r a c t e r iz e d b y e x p l o i t a t i o n o f g ra p h i c a lr e p r e s e n t a t io n s . T h e m a i n g o a l o f th e e x p e r i m e n t w a s t o o b s e r v e a n d r e c o r dh o w d e s i g n e r s a c t u a l l y m a n i p u l a t e g i v e n d e s i g n r e p r e s e n t a t i o n s i n r e - r e p -r e s e n t a t io n a l p r o c e s s e s o f a d a p t a t io n . A d a p t a t i o n w a s d e f i n e d a s t h e t a s ko f t r a n s f o r m i n g a g i v e n d e s i g n r e p r e s e n t a ti o n ) t o m e e t c h a n g i n g c o n -s t r a i n t s . T h e c h o s e n t a s k d o m a i n w a s s p a t i a l c o n f i g u r a t i o n i n p l a n d e s i g n .T h e c o m p l e x n a t u r e o f i n f o rm a t i o n i n t h e g r a p h i c a l r e p r e s e n t a t i o n o fd e s i g n s r a i s e d s e v e r a l r e s e a r c h i s s u e s . A n a d d i t io n a l o b j e c t i v e o f t h ee x p e r i m e n t w a s t o s t u d y t h e w a y d e s i g n e r s d e a l w i t h t h i s ri c h n e s s o f i n f o r -m a t i o n i n g r a p h i c r e p r e s e n t a t i o n s , a n d t h e w a y t h e y m a n i p u l a t e g r a p h i c a ls y m b o l s a s a b s t r a c t k n o w l e d g e d u r i n g t h e a d a p t a t i o n o f d e s i g n d r a w i n g s .

T h e o v e r a l l o b j e c t i v e w a s t o p r o v i d e a n a c c o u n t o f t h e r e p r e s e n t a t io n se m p l o y e d , t h e o p e r a t i o n s u s e d a n d t h e w a y t h e y w e r e c o n t r o l l e d i n t h ea d a p t a t i o n p r o c e s s . T h e f i n d i n g s w e r e s u b s e q u e n t l y a n a l y z e d a n d c a t e g o r -i z e d f o r k i n d s o f r e p r e s e n t a t i o n a l m o d i f i c a ti o n s , t h e s t r a t e g i e s a n d o p e r -a t i o n s e m p l o y e d a n d t h e w a y t h e y i n t e r a c t i n t h e p r o c e s s . F i n a l l y , i t w a sp o s s i b l e t o p o s t u la t e t h e p a r t i c u l a r s t r u c t u re s o f r e p r e s e n t a t i o n w h i c h m a k eg r a p h i c r e - r e p r e s e n t a t i o n p o s s i b l e i n t h e s e t a s k s .

E a c h o f t h e d e s i g n e r s i n th e e x p e r i m e n t w a s r e q u e s t e d t o fo r m u l a t e a n dc o n s t r u c t e x p l i c i t r e p r e s e n t a t i o n a l s t r u c t u r e s i m p l i c i t i n t h e r e p r e s e n t a t i o nw h i c h , f o r h im / h e r , e n a b l e d t h e m a k i n g o f c h a n g e s . S u b j e c t s w e r e a l s oa s k e d t o r e c o r d e a c h o f t h e i r g r a p h ic a l m a n i p u l a t i o n s a n d r a t i o n a le . T h u s ,b o t h t h e r e p r e s e n t a t io n a l s t r u c tu r e s e m p l o y e d i n r e a s o n i n g b y t h e d e s i g n e r sw e r e i d e n t i f i e d a n d t h e r e s u l t i n g p r o c e d u r a l m a n i p u l a t i o n s w e r e r e c o r d e d .



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2 Baharat, D, Schmit t , G,Fal t lngs, B end Smith , I 'Case-based design in architecture' inJ Ger o en d F S u d weeks (ed s )AID 94 Kluwer, Do rdracht (1994)pp 145-1623 Hu e, K, Smith, I , Faltlngs,B, Shil l , S and Schmltt , G'Adaptat ion of spa t ia l des ign

cases in J S Gero (ed) AI i nDesign 92 Kluwe r, Dordracht ,(1992)14 Oxmen, R E 'Des ign shells:a formalism for proto typeref inement in knowledge-baseddesign systems' Artificial Intelli.gence in Engineer ing Vol 519(1990) pp 2-8.15 Oxman, R E 'Des ign case-bases: g raph ic knowledge basesfor design worksbaca' in M Tan(ed) CAAD Futures '95 Com-pute r Aide d Archi tectural DesignSingapore (1995)

T he sub je c t s w e r e a dva nc e d s tude n t s i n a r c h i t e c tu r e . T he y w e r e r e qu i r e dto a da p t a g ive n de s ign on the ba s is o f c ha ng e d r e qu i r e m e n t s . T h e r e qu i r e dc h a n g e s w e r e p u r p o s e l y k e p t m i n i m a l i n o r d e r t o e n h a n c e u n d e r s t a n d i n go f t he c om ple x be ha v io r i n a da p ta ti on . T h e p r ob le m w a s t o r e duc e t he a r e ao f a g ive n p l a n d r a w ing by 20 . I n suc h a l im i te d p r ob le m s t a t e m e n ts tude n t s c ou ld e a s i l y e xp lo r e d i f f e r e n t so lu t i on spa c e s a nd a c c u r a t e ly r e c -o r d t he i r de c i s ion - m a k ing r a t i ona l e .T he sub je c t s w e r e a ske d to p r ov ide s e l f - p r o toc o l s r e c o r d ing e xp l i c i t s t e p s ,a c t i ons a nd r e a son ing . T he p r o toc o l s w e r e l a t e r f o r m a l ly r e c o r de d in aC A D g r a ph ic s sy s t e m to p r ov ide a s e que nc e o f r e -r e p r e se n t a ti ons sup -p l e m e n te d by a nno ta t e d t e x tua l exp la na t ions . M u l t i p l e r e p r e se n t a ti ons w e r em a de e xp l i c i t i n t he s e que nc e . A t a l a t e r s t a ge, t he g r ou p o f pa rt i c ipa n t sc on t r ibu t e d i n t he de ve lopm e n t o f a j o in t m ode l .4 2 ssumpt ionsA n unde r ly ing the o r e t ic a l a s sum pt ion i s t ha t t he f o r m o f t he g r a ph ic r e p -r e se n t a ti on o f de s igns a nd the i r a m e na b i l i t y t o a da p ta t i on a r e r el a te d . T h ef o r m o f re p r es e n ta t io n e n c o d e s i n f o r m a t i o n a n d k n o w l e d g e w h i c h s u p p o r tr e a son ing du r ing m a n ipu la t i on . T he r e f o r e , i n o r de r t o a s s i s t p r oc e s se s o fr e a son ing in t he a da p ta t i on o f de s ign d r a w ings , a nd in o r de r t o be r e spon -s ive t o m a n ipu la t i ons , g r a ph ic r e p r e se n t a ti ons m u s t be e xp l i c i t l y s t r uc tu r e d .A c c o r d ing to t he se m a in t he o r e t i c a l a s sum pt ions , t he f o l l ow ing c onc e p t sa r e p r opose d a s t he t he o r e t i c a l ba s i s o f t he r e se a r c h .4 2 1 Mult iple representat ions as underlying abstract ionlevelsO ne de f in it i on o f a da p ta t i on i s t ha t t he c u r r e n t g r a ph ic s t at e o f t he r e p r e sen -ta t ion i s manipula ted unt i l a f i t i s achieved wi th the new requirements . Ino r de r t o suppo r t ope r a t i ons o f r e - r e p r e se n t a t i on w e p r opose t ha t g r a ph icr e p r e se n t a t i ons m us t be e xp l i c i t l y s t r uc tu r e d . T he c onc e p t o f m u l t i p l e r e pr e s e n t a t i o n s a s u n d e r l y i n g a b s t r a c t i o n l e v e l s i s th e c o n c e p t w h i c h w e p r o -p o s e f o r a c c o m m o d a t i n g s e m a n t i c k n o w l e d g e i n g r a p h ic s .I n t he pa r t ic u l a r de s ign t a sk w e c a n o bse r ve a s t r uc tu r e o f m u l t i p l e und e r ly -ing , o r ba c kg r ound , r e p r e se n t a ti ons . T he se c a n be d i f f e r e n t k inds o f ge ne r ica bs t r a c ti ons o f t he de s ign r e p re se n t a ti on . V a r ious w o r ks ha ve be g un toa dd r e s s t he r o l e o f suc h a bs t r a c t i ons i n de s ign a nd to de m ons t r a t e t he i ru t i l i t y i n a da p ta t i on . F o r e xa m ple , suc h de sc r ip t i ons i nc lude ge om e t r y -ba se d de sc r ip t i ons o f spa t ia l a gg r e ga t ions , t opo log ic a l de sc rip t i ons o f spa -t ia l r e la t ions 12, gram m ar-ba sed desc r ip t io ns ~3 and typo logi ca l d esc r ip t ionssuc h a s h ous ing s c he m a ~4 e t c . O the r w o r k on a da p ta t i on i n C B R H ha s



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p o i n t e d o u t t h e s i g n i f ic a n c e a n d r o l e o f g e n e r a l k n o w l e d g e o f a d a p t a t io np r o c e d u r e s i n a t a s k . I n t h i s v i e w , a d a p t i v e k n o w l e d g e c a n b e r e g a r d e d a st h e a b i l i t y t o m a n i p u l a t e h o l i s t i c d e s i g n s w h i c h u n d e r l i e t h e u n i q u ea r r a n g e m e n t a n d r e l a ti o n s hi p s o f c o m p o n e n t s .T h e r a n g e o f p r o c e s s e s o f a d a p t a t i o n i n d e s i g n s h o u l d p r e s e r v e a n d e x p l o i tt h e s i g n i f ic a n t a s p e c t s o f a d e s ig n b y m a i n t a i n i n g t h e i n t e r n a l c o n s i s t e n c yo f it s c o n c e p t u a l s o l u t io n . I n t h is e x p e r i m e n t w e h a v e s u g g e s t e d t o d e c o m -p o s e a d e s i g n d r a w i n g t o i ts s t ru c t u re s . T h e d e c o m p o s i t i o n o f d e s i g n d r a w -i n g i n t o d i f fe r e n t s t r u c tu r e s o f k n o w l e d g e i s, in f a c t , d e c o m p o s i t i o n o fd i f f e r e n t t y p e s o f k n o w l e d g e . D e s i g n d r a w i n g s a r e u s u a l l y n o t r e a d i l yd e c o m p o s a b l e i n t o s e p a r a t e r e p r e s e n t a t i o n s , o r s t r u c t u r e s . I n o r d e r t o i s o -l a t e i m p l i c i t r e p r e s e n t a t i o n a l s t r u c t u r e s i t i s i m p o r t a n t t o i d e n t i f y t h ee x p l i c i t r e p r e s e n t a t i o n s w h i c h s u p p o r t v i s u a l r e a s o n i n g . S i n c e d r a w i n g s a r en o t e x p l i c i t l y s t r u c t u r e d a c c o r d i n g t o t h o s e r e p r e s e n t a t i o n s , i t i s s i g n i f i c a n tt o e x t e r n a l i z e t h e m i n r e - r e p r e s e n t a t i o n . I n o r d e r t o a s s i s t p r o c e s s e s o fr e a s o n i n g i n t h e a d a p t a t i o n o f d e s i g n s w e h a v e e x p e r i m e n t e d w i t h th ee x p l i c a t i o n o f u n d e r l y i n g s c h e m a i n g r a p h i c r e p r e s e n t a t io n s b y r e q u e s t i n gt h a t t h e s u b j e c t s m a k e t h e m e a c h a b s t r a c t i o n l e v e l) i n d iv i d u a l l y e x p l i c it .I n t he f i n a l C A D f o r m a l r e c o n s t ru c t i o n o f t h e p r o c e s s t h e s e m u l t i p l e r e p -r e s e n t a t i o n s w e r e a c t u a l l y p l a c e d o n s e p a r a t e l a y e r s . W e h a v e a l s oa t t e m p t e d t o g e n e r a l i z e r e g a r d i n g t h o s e s t r u c t u r e d r e p r e s e n t a t i o n s w h i c hr e c u r r e d w i t h i n t h e g r o u p o f s u b j e c ts , a n d m a y b e c o n s i d e r e d r e l e v a n t a sd o m a i n k n o w l e d g e .

4 2 2 Internal consistencyD u r i n g a d a p t a t i o n , t h e d e s i g n m u s t r e m a i n i n t e r n a l l y c o n s i s t e n t i n o r d e r t os a t i s f y v a r i o u s c o n s t r a i n t s . C o n s t r a i n t s i n e v o l u t i o n m a y b e d e r i v e d f r o md i f f e r e n t s o u r c e s . W e h a v e i d e n t if i e d t w o k i n d s o f a d a p t a t i o n c o n s t r a i n ts :e x t e r n a l g i v e n c o n s t r a i n t s , a n d i n t e r n a l d e r i v e d c o n s t r a i n t s .

- - e x t e r n a l c o n s t ra i n t s a r e i m p o s e d f r o m t h e p r o b l e m d e f i n it i o n , a n da r e e x p l ic i t l y r e p r e s e n t e d i n t h e p r o b l e m s t a t e m e n t . F o r e x a m p l e , c o n -s t r a i n t s b e t w e e n d e s i g n a n d d e s i g n e n v i r o n m e n t , s u c h a s t h e s i t e i na r ch i tec tu r e 1 2.- - i n t e r n a l c o n s t r a i n t s a r e d e r i v e d a s a c o n s e q u e n c e o f a n e a r l i e rd e s i g n m a n i p u l a t i o n . F o r e x a m p l e , e a c h c h a n g e i n c o m p o n e n t s a n dt h e i r re l a t i o n s h ip s c a n i m p o s e n e w c o n s t r a in t s . I n t e r n a l c o n s t r a in t s a r ei m p l i c i t c o n s t r a i n t s t h a t a r e b a s e d o n d o m a i n k n o w l e d g e , t h e i r r o l e i st o k e e p t h e c o n s i s t e n c y a m o n g t h e m u l t i p l e i n t e r n a l r e p r e s e n t a t i o n s .I n t e r n a l c o n s t r a i n t s a r e u s u a l l y p r o p a g a t e d b y o t h e r c o n s t r a i n t s w h i c he m e r g e d u r i n g t h e p r o c e s s . T h e a b i l i t y t o m a n i p u l a t e c o n s t r a i n t s c a nb e r e g a r d e d a s a s i g n i fi c a n t k i n d o f a d a p t a t i o n k n o w l e d g e . T h e



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de s igne r m us t i de n t i f y t hose r e a son ing p r oc e s se s t ha t m a in t a in t hec ons i s t e nc y o f t he i n t e rna l r e p r e se n t a t ions .

I f a de s ign is t o r e m a in c ons i s t e n t i t shou ld s a t i s fy bo th e x t e r na l a ndin t e r na l c ons t r a in t s . I t i s t he a b i l i t y t o ha nd le c ons i s t e nc y by the m od i f i -c a t i on o f s tr uc tu re s c om pone n t s a nd c ons t r a in t s at a ny tim e tha t c ha r a c -t e r iz e s t he dyna m ic na tu r e o f t he p r oc e s s o f a da p ta ti on . W i thou t c on t r o l l i ngthe im p a c t o f i n t e r nal c o ns t r a in t s be tw e e n the d i f f e re n t m u l t i p le r e p r e se n -t a t ions i n t e rna l c ons i s t e nc y c a nno t be m a in t a ine d .

W i th e a c h r e - r e p r e se n t a t i on ne w in t e r na l c ons t r a in t s e m e r ge . I t m a y a l sobe ne c e s sa r y t o v io l a t e t he c ons t r a in t s w h ic h a r e im pose d by the ne w r e p -r e se n ta t i on . I n t he e xpe r im e n t on e goa l w a s t o unde r s t a nd the r o l e o f de s ignc ons t r a in t s i n r e -r e p r e se n t a ti on a nd how the i n t e rna l c ons i s t e n c y a nd in t e g -r i ty of the des ig n i s ma in ta ine d du r ing i t s evolu t ion . I t i s th is ab i l i ty toh a n d l e c o n s i s t e n c y b y m o d i f i c a t i o n s u n d e r c o n d i t i o n s o f d y n a m i c c o n -s t r a in t p r opa ga t ion tha t c ha r a c t e r i z e s one a spe c t o f c r e a t i ve de s ign .4 2 3 Modification strategies and operationsA nothe r r e se a r c h i s sue w a s t o c ha r a c t e r i z e m od i f i c a t i on s t r a t e g i e se m p loye d o r p r e f e r re d by the sub je c ts . C a n the se s t r a te g i e s p r ov ide a t a x -onom y f o r de s ign a da p ta t i on? W e be l i e ve t ha t i t i s pos s ib l e t o de f inec l a s se s o f s t r at e g i e s a nd ope r a t ions . T he se a r e ba se d u pon type s o f m od i f i -c a t i on r e l a ti ve t o t he unde r ly ing r e p r e se n t a t i ona l s c h e m a a nd c ons t r a in ts . I na dd i t i on t o m od i f i c a t i on o f st r uc tu r e s o f a de s ign the a b i li t y t o m a n ipu la t ec ons t r a in t s c a n a l so be r e ga r de d a s a s ign i f i c a n t k ind o f a da p ta t i on know l -e dge . F o r e xa m ple a da p ta t i on m a y be a pp l i e d t o c ons t r a in t s by w e a ke n ingp r e f e r e nc e s a nd p r io r i t i e s . W e ha ve be e n a b l e t o d r a w on ly l im i t e d c on -c lu s ions on th i s sub j e c t w i th ou r r e l a t i ve ly sm a l l popu la t i on o f s tude n tde s igne r s. H ow e ve r i t a ppe a r s t o u s tha t t he c ogn i t i ve m a s t e r y o f g r a ph ic a la da p ta t i on ope r a t i ons a nd sc he m a m o d i f i c a t ion s t r a te g i e s i s one o f thef o r m s o f de s ign e xpe r t i s e .

4 2 4 The dynamics of re representationE a c h ne w a da p ta t i on ope ns t he pos s ib i l i t y f o r f u r the r i n t e r a c t i ons a nd ne wc ha nge s . I n suc h a n a pp r oa c h d ive r s i ty a r is e s w he n oppo r tun i t ie s f o r ne win t e r a c t ions t ha t c a n be e xp lo i t e d a r e r e c ogn iz e d by the de s igne r a s a ne ve r - c ha ng ing pa t t e rn o f pos s ib i l it i es .

5 Re Representing the new from the known: a casestudy in architectural re representationI n o r de r to te s t a nd va l ida t e ou r a ssum pt ions a n e m p i r i c a l r e se a r c h w a sc ons t r uc t e d . I n t he e xpe r im e n t dom a in kno w le d ge m a de m a n i f e s t i n

338 D e s ign S tud ie s V o l 18 N o 4 O c tobe r 1997


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gr a ph ic a l ope r a t i ons i n a de s ign t a sk w a s s tud i e d . R e p r e se n t a t i ons i n a r c h i -t e c tu r e t e nd to be t a sk spe c i f i c . E a c h t a sk ha s i t s ow n r e p r e se n t a t i ona lsy s t e m w h ic h suppo r t s r e a son ing p r oc e s se s w i th in t he t a sk dom a in . T hec a s e s t u d y th a t w a s c h o s e n w a s a h o u s e p l an , t h e c o m p l e x i t y o f w h i c h w a se a s i l y m a na ge a b le by the sub je c t s . T he t a sk dom a in w a s spa t i a l c on f igu r -a t i on , o r the f o r m a l a nd f un c t iona l m o d i f i c a t ion o f t he de s ign r e p r e se n t a t iono f t he p l an . T he sub je c ts , w ho w e r e 15 a dva n c e d l e ve l a r c h i te c tu r a l s t u -de n t s , w e r e r e que s t e d t o do the f o l l ow ing a s s ignm e n t . G ive n a n e x i s t i ngde s ign r e p r e se n t a ti on p l a n d r a w ing ) :

1 ) T o c ons t r uc t a s e t o f unde r ly ing m u l t i p l e r e p r e se n t at i ona l a b s t r a c ti onl e ve l s f o r t he g ive n de s ign . E a c h a bs t r a c t i on l e ve l sugge s t e d de s ignope r a t i ons a s soc i a t e d w i th t he t ype o f know le dge o r de s ign p r inc ip l e .F o r e xa m p le , a n unde r ly ing a b s t r a c ti on suc h a s a n a x i s w h ic h i s a s so -c i a t e d w i th sym m e t r y m a y a l so be a s soc i a t e d w i th ope r a t i ve know l -e dge suc h a s m or pho log ic a l t r a ns f o r m a t ions r e l a t i ve t o a x i a l o r de r .I n t he c a se s tudy , c e rt a in c l a s se s o f a bs t r a c ti on c om m on in t he dom a inw e r e sugge s t e d a s e xa m ple s , w h i l e t he sub je c t s w e r e r e que s t e d t of o r m u la t e o the r s c he m a o r a bs t r a c t i on l e ve l s w h ic h w e r e r e l e va n t t othe i r ow n r e - r e p r e se n t a t i ona l ope r a t i ons . C e r t a in t yp i c a l s c he m a o rabs t rac t ion leve ls in the dom ain a re F igure 1) :

underlying abstractions of order f o r e xa m ple : m a in r e c t a ngu la r a x i s , s e c -onda r y d i a gona l a x i s sy s t e m , m a in g r id sy s t e m , e t c .

Fig ur e I Abstra~: t ion leve lsa s r e r e p r e s e n t a t i o n a l s y st e m s i n d e s i g n

comers d i a g o n a l a x i s o r t h o g o n a l a x i ssyst em syst em

formal ye rs emphas ized main gr id syst emaxis

D e s ign by r e - r e p re se n t a t i on 339


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typological schema ( t ypo log ie s i n hous ing de s ign ) : f o r e xa m ple , t hek n o w l e d g e o f m i n i m a l a n d m a x i m a l d i m e n s i o n s o f f u n c t i o n a l e l e m e n t ssuc h a s be d r oom , ba th r oom , s t a i r s e t c .underlying abstract ions of order in schema f o r e xa m ple , p r inc ip l e s o f z on -ing , f unc t iona l r e l a t i ons suc h a s l i nka ge s be tw e e n r oom s , e t c .general design principles related to the task f o r e xa m ple , t he r e duc t iono f c om e r s , l a ye r ing sy s t e m s , e m p ha s i z ing the m a in a x i s , e tc .( 2 ) G ive n a n e x t e rna l re qu i r e m e n t , t he sub je c t w a s r e que s t e d t o i de n t i f y

de s ign c ons t r a in t s a n d to s e l e c t a b s t r ac t i on l e ve l s f o r r e -r e p r e se n t a ti onwhich were re la ted to these cons t ra in ts . In th is case , the exte rna lr e qu i r e m e n t w a s t o de c r e a se t he a r e a o f t he p l a n de s ign by 20 . T hesub je c t s i de n t i f i e d t he c ons t r a in t s a nd m os t de c ide d to p r e se r ve t hetopo log ic a l r e l a ti ons o f the d e s ign w h i l e e f f e c t i ng t he r e - r e p r ese n -tations.

(3) Af te r f i rs t r e - representa t ions we re e f fec ted , the des ign s were eva lu-a t e d a nd f a u l ts w e r e i de n ti f ie d . F o r e xa m ple , t he f unc t iona l t ype s m a yha ve ' f a i l e d ' f unc t iona l ly o r f o r m a l p r inc ip le s suc h a s t he d im e ns ionso f g r id s y s t e m m a y h a v e b e e n ' v i o l a te d ' .

( 4 ) A t t h is s t a ge the e m e r g ing in t e r na l c ons t r a in ts w e r e ide n t i fi e d a ndne w r e - r e p re se n t a t ions w e r e und e r t a ke n . I n t h is w a y a c yc l i c a l p r oc e s so f c ha nge s p r opa ga t e d n e w c ons t r a in t s , w h ic h e l i c it e d subse que n tm od i f i c a t i ons a c t i va t e d by the va r ious know le dge sou r c e s .

o r i g in a l d e s i g ninitial state

a d a p te d d e s i g nf m a l s ta te

Figure Initial and adapted final state



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Figu re 2 i l lus t ra tes the in i t ia l s ta te and the f ina l s ta te of th is subjec t .T he r e - r e p r e se n ta t i on s e que nc e o f t he sub je c t s e x a m p le i l lu s t r at e d i n t h ispa pe r , i nc lude d som e tw e n ty - e igh t r e c o r de d i t er a ti ons . T he f i r s t s i x r e - re p -r e se n t a t i ons a r e i l l u s t r a t e d i n F igu r e 3 a nd de sc r ibe d be low . E a c h r e - r e p -r e se n t a t ion g e ne r a t e s a s e que nc e o f i n te r na l c ons t r a in t s w h ic h m us t be s a t -i s f ie d i n t he ne x t r e - r e p r e se n t a ti on a nd th i s c on t inue s i n a c yc l e o f ske t c he sunt i l a l l cons t ra in ts a re sa t i s f ied inc luding the in i t ia l cons t ra in t .

re representat ion 0 to 1: ( c om pone n t s a f f e c t s t r uc tu r a l s c he m a )In i t ia l cons t ra in t i s a r educ t ion of s ize . The in i t ia l s t r a tegy was to s ta r t ther e duc t ion p r oc e s s o n the ho l i s t ic s t r uc tu re . T h e inne r l a ye r , one o f a s e t o ff o r m a l l a ye r s w h ic h c on ta in f unc t iona l z one s ( c ou r t ) w a s r e duc e d to a m in i -m a l f unc t iona l s i ze . T h i s ope r a t i on d i s tu r be d the c ons i s t e nc y o f t he g r idsys t e m ;

re represen tat ion 1 to 2: ( s t r uc tu r a l ope r a t i on a f f e c t s c om pone n tin tegr i ty)I n o r de r t o r e c ons t r uc t t he r e gu la t i on sy s t e m the r e s t o f t he f unc t iona l l a ye r sw e r e sh i f t e d a long the d i a gona l a x i a l sy s t e m . A s a r e su l t som e typo log ic a lc o n s t r a i n t s e m e r g e d b y c h a n g i n g t h e d i m e n s i o n s o f f u n c t i o n a l s p a c e s(ent rance cor r idor ) and a rchi tec tura l e lements ( f i r ep lace ) ;

re representa t ion 2 to 3: ( pa r a m e t r i c m od i f i c a t ion )T he e x t e ns ion o f a f unc t iona l spa c e ( e n t ra nc e c o r r ido r ) w a s m a de in c o r r e -l a t i on w i th t he d i a gona l sy s t e m a nd a x i s ;

re representat ion 3 to 4: ( pa r a m e t r i c m od i f i c a t i on o f c om pone n t )A r c h i t e c tu r a l e l e m e n t ( f i r e p l a c e ) w a s t r a ns f o r m e d to o r ig ina l s i z e i nre la t ion to cent ra l ax is ;

re representa t ion 4 to 5: ( t opo log ic a l a nd f unc t iona l r e l a t i onsh ip s )

T he e n l a r ge m e n t o f one e l e m e n t ( f i r ep l a c e ) ha s a f f e c t e d r e l at i ons be tw e e na r c h i t e c tu r a l e l e m e n t s ( c o lum n a nd f i r e p l a c e ) , a nd r e qu i r e d a subse que n tc ha nge in r e l a t e d e l e m e n t s ;

re representat ion 5 to 6: ( f o r m a l sy s t e m a nd pa r a m e t r i c r e duc t ion )T h e c o l u m n s w e r e s h i f t e d s y m m e t r i c a l l y a n d t h e t w o a d j a c e n t s p a c e sw e r e r e duc e d .

D e s ign by r e - r e p r e se n t at i on 341


14/19

. . . . . . - l

i n i t i a l s t a t e

r ~ r ~l ' I i :l

, L r qn o 1

" " ~" ' ~ . ' U ~ ' ~ ' 1

n o 2

I - % I t - 7 1 ~ \ , ; . , ' m

n o . 3

In o 4 n o 5

Figure 3 Re-representation on transformations analysis don e by Am os W achman, Fac ulty of Arch itecture and TP, Technion)

342 D e s ig n S tud ie s V o l 18 N o 4 O c to be r 1997


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5.1 FindingsH um a n de s igne r s w e r e f ound to be a b l e t o e x t r a c t va r ious a bs t r a c t e de xp l i c i t r e p r e se n t a t ions o f t he e x i st i ng de s ign ba se d on the i r ow n dom a inknow le dge . T he se a bs t r a c t i ons i nc lude d typo log ic a l s c he m a , o r ga n iz a t iona lp r inc ip le s , m or pho log ic a l p r inc ip l es , f unc t iona l r e l a t i onsh ip s , e t c . S ub je c t sw e r e a l so a b l e t o e x t e r na l i z e a nd c a t e go r i z e t he i r g r a ph ic m a n ipu la t i onsc onc e p tua l ly de sp i t e t he f a c t t ha t d r a w ings t e nd no t t o p r ov ide e xp l i c i tr e p r e se n t a t i ona l i n f o r m a t ion to suppo r t suc h de c om pos i t i on . F u r the r m or e ,t he g r a ph ic a l r e - r e p r e se n t a t i on o f a de s ign e xp lo i t s t h i s s a m e know le dgein c r e a t i ng ne w r e p r e se n t a t ions .F r om ou r r e se a r c h i t a ppe a r s t ha t hum a n de s igne r s u t i l i z e a pe r sona l h i e r -a r c h i c a l o r de r o f unde r ly ing c onc e p tua l s t r uc tu r es suc h a s g r id s , c ons t r uc -t i on l i ne s e tc . T he se m u l t i p le s c he m a t i c r e p r e se n t a ti ons s e r ve t he de s igne ras supportive representations f o r de s ign m a n ipu la t ion . I t is t he s t r uc tu r ingqua l i t y o f t he se m u l t i p l e r e p r e se n t a ti ons a nd the e xp l i c a t i on o f t he i r i nd i -v idua l i n t e rna l c ons t r a in t s ( t he i n te r na l l og i c o f t he s c he m a ) w h ic h a ppe a rto suppo r t de s ign m a n ipu la t i on .T he a da p ta t ion , o r m od i f i c a t ion , o f r e p r ese n t a t ions a l so a ppe a r s t o bedependent upon generalized domain know ledge which is learned throughdesign experience I n t he pa r t i c u l a r de s ign to be a da p te d , t h i s ge ne r a l i z e dknow le dge e na b le d the e x t e r na l i z a ti on / c ons t r uc t ion o f t he unde r ly ingsc he m a o f t he de sign . T he se ( va r ious ) s c he m a c ons t i t u t e t he multipleunderlying representations of t he de s ign . A c c o r d ing to ou r f i nd ings , e a c hde s ign m us t ha ve suc h m u l t i p l e r e p r e se n t a t i ons , i f i t i s t o suppo r t t hem a n ipu la t i on o f de s igns .T h i s a bs t r a c t know le dge m a y be c ons ide r e d a n i n t e r - r e l a t e d sy s t e m o fdom a in spe c i f i c r e p r e se n t a t i ona l s t r uc tu r e s . T h i s f i nd ing i s m os t r e l e va n tto t he p r ob le m o f a pp r op r i a te r e p r e se n t a ti ons f o r de s igns . A no the r o f them o s t i n t e re s t i ng obse r va t ions w a s t he c on t inge n t qua l it y o f t he a da p ta t ionp r oc e s s . I t w a s po s s ib l e t o obse r ve how e a c h ne w ( m od i f i e d ) r e p r e se n t a ti ono f t he de s ign in t r oduc e d ne w m od i f i c a ti on s t r at e g i es a nd ope r a t i ons , a nde ve n ne w s t r uc tu r ing c onc e p t s . R e c o gn i t i on a nd m a in t e na nc e o f t he in t e r na lc ons i s t e nc y o f the sy s t e m o f a bs tr a c t ions w a s f o und to be a c ha r a c t e ri s t i co f de s igne r s c ogn i t i ve a b i l it y . T he a b i l i ty t o r e la t e t o th i s s c he m a a s ar e f e r e nc e a nd to u se o r de pa r t f r o m i t is a qua l i t y o f t he c r e a ti ve de s igne r .

Towards a general model o f reasoning in rerepresentat ionI n o r de r t o de ve lo p a ge ne r a l m o de l w e r e c o r de d the s t a t es o f e vo lu t iono f t he de s ign r e p r e se n t a t i ons a s w e l l a s t he p r o toc o l s o f i n te r a c t ions

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be tw e e n the de s igne r a nd the s e m a n t i c r e p r e se n t a ti ons . The m ode l i s i t er a t-i ve a nd c ons i s t s o f t he f o l l ow ing m a in s t a ge s :1 )

(2)

Ex te r na l C ons t r a in t s : i de n t i f ic a t ion o f e x t e r na l c ons t r a in t s . E x te m a lc ons t r a in t s a r e ge ne r a l l y de r ive d f r om the p r ob le m de f in i ti on o r r e -def init ion.I n i ti a l S t r a t e gy : s e l e c t i on o f r e -r e p r e se n t a ti on s t r a t egy , i nc lud inga m ong o the r s , s t r uc tu r a l m od i f i c a t i on o f t he s c he m a , o r c om pone n tr e - r e p r e se n t a t i on w i th in t he s c he m a . I n de s ign the r e i s a lw a ys som ef o r m o f h i e r a r ch i c a l r e l at i onsh ip be tw e e n s t r uc tu re a nd c om pone n t .Thus t he s e l e c t ion o f w or k ing w i th in t he a bs t r a c ti on l e ve l s o f t hesc he m a s t r uc tu r e , o r m od i f y ing the s c he m a de pe nds upon the de s ign -e r s e va lua t ion o f the e x t e r na l c ons t r a in t . I t m a y a l so be de t e r m ine dby pe r sona l de s ign p r e f e r e nc e s .

I t i s t he a b i l i t y t o ha nd le c ons i s t e nc y by the m od i f i c a t i on o f s t r uc tu r e s ,c om pon e n t s a nd de s ign c ons t r a in t s w h ic h i s c ha r a c t e ri s t i c o f r e -r e p r e se n -t a t i on . The s t r a t e gy m us t be de t e r m ine d by the o r de r i n w h ic h to a c h i e vem od i f i c a t i on . A c on s t r a in t m a y be v io l a t e d by a da p t ing a va lue o r by m o d-i f y ing the s t r uc tu r e a nd i t m a y a l so be pos s ib l e t o s im p l i f y a p r ob le m byre laxing a cons t ra in t .( 3 ) R e p r e se n t a t i ona l A bs t r a c t i on La ye r : s e l e c ti on o f l a ye r o f r e p r e se n -

t a t i on o f s c he m a , a bs t r a c t i on l e ve l , o r i nd iv idua l c om pone n t . I n ge n -e r a l, t he c ons t r a in t s spe c i f y p r ope r t i e s o f t he de s ign tha t m us t b et r a ns f o r m e d . S uc h p r ope r t i e s m a y be r e s t r i c t i ons on va lue s , o rr e l a t i onsh ip s be tw e e n d i f f e r e n t c om pone n t s , a nd he lp t o de t e r m ineupon w h ic h r e p r e se n t a t i ona l l a ye r t he r e - r e - r e p r e se n t a t i on c a n bee f fec ted .

( 4 ) O pe r a t i ona l M e thod : s e l e ct i on o f ope r a t i ona l m e tho d a s soc i a t e d w i ththe r e p r e se n t a t i ona l l a ye r . The c ons t r a in t ( s ) gu ide t he ope r a t i ons ona r e p r e se n t a t i on du r ing the m od i f i c a t i on p r oc e s s . F o r e xa m ple , t ypo -log i c a l subs t it u t i on r e t r ie ve s r e f ine m e n t m e thod s ; t opo logy r e t r i e ve stopo log ic a l ope r a t i ons suc h a s de l e t e , i n se r t a nd pa r a m e t r i c ope r -a t i ons ; c ha nge in a f o r m a l sy s t e m r e t r i e ve s i t s ow n f o r m a l r e p r e se n -ta t iona l sys tem.

( 5 ) Eva lua t ion : e va lua t ion o f i n t e rna l c ons i s t e nc y w i th r e spe c t t o r e p -r e se n t at i ona l i n t e g r i ty , f o r e xa m ple , i n t he f o r m a l s t r uc tu r e o f ades ign .

(6) In te rna l Con st ra in ts : ident i f ica t ion of in te rna l cons t ra in ts whiche nsu r e i n t e r na l i n t e g r i t y . The na tu r e o f a c ons t r a in t a f f e c t s t he w a yr e - r ep r e se n t a t ion m a y be pe r f o r m e d . A r e - r e p r e se n t a t ion s t r a t egy m a ya l so be i nvo ke d in r e spon se t o t he v io l a t i ons o f the c ons t r a in t .



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(7) Select ion: s elect io n of act ive constraints ac cord ing to priori ty cri teria.(8 ) Co n t inue cycle .F i g u re 4 d e s c r i b e s s o m e o f th e ab s t r ac t io n l ev e l s an d t h e ir a s s o c i a t ed o p e r -a t ional methods . The genera l model i s schemat ica l ly i l lus t ra t ed by onecyc le o f re -represen ta t ion in Figure 5 .

Summary and conclus ions: the creat iv i ty in rerepresentat ionOu r work has exp lo red the sc ient if ic me ans th rough wh ich our owni nt ui ti on ab o u t d e s i g n can b e t r an s fo rmed i n to t h e d ev e l o p m en t o f a t h eo r -e t i ca l approach . We have p resen ted the theore t i ca l and empi r i ca l foun-dat ions fo r re - represen tat ion m odel s o f adap t ive des ign . In the em pi r i ca ls t u d y an ap p ro ach t o t h e mo d e l i n g o f t h e d e s ig n r ea s o n i n g u n d e r l y i n g r e -represen ta t ional p roce sses th rough sequen ti a l d rawing an d ske tch ing o f re -represen ta t ions has been descr ibed .

The em pi r i ca l s tudy has l ed to the cons t ruc t ion o f a genera l m odel o f re -representation exp loi t ing mult iple representations o f the abstra ct ion leve lsin des ign . T he m odel i s base d on the t rans format ion o f chunks o f know l -edg e in des ign in to exp l i c i t re -represen ta t ional s truc tu res wh ich can su ppor tthe creat ive ac t of re-representat ion in a graphic environment .

som e bstr ction levels ndschem which suppo rt mult iplerepresent tion l systems

t y p o l o o c a lschem

b a t h r o o m b e d r o o m c o r r id o r

t o p o l o g y f o r m l sys tem

r el at io n s 1[ s iz e ] [ c o n c e p t Iins ide larger central , l inear, axia loutside smal ler

refmementspecializationgener al i7~ion o n l li n s e r t i o n I o p e r t i o n s sca l ingopera t ionsan dparametricad j u s t men t f o r m a ls y s t e ms y m m e t r yo p e ra t i o n sFigure Abstraction levels and their associated operational methods

De s ign by re-- represen ta tion 345


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s e l e c ti n i t i a l

c o n s t r a i n

s e l e c ti n i t i a l

s t r a t e g y

s c h e m ac o m p o n e n t ]

ss ignpr i od t y

Figure 5 General model of re representation

select firstrepresent t ion lbs tr c t ion levelt y p o l o g y [t o p o l o g y ]

I f o r m a l ]

s e l e c ta s s o c i a t e doper t ions pe c i a l i z a t i on /ge ne r a l i z a t i on I

i n s m i o n /d d i f i o nI pa r a m e t r i c [

ev lu tec o n s t r a i n t s

T h e s e q u e n t ia l m a n i p u l a t io n s o f g r a p h i c a l r e p r e s e n t a ti o n s a n d t h e a b i l it yt o r e - d e s c r ib e m u s t b e c o n s i d e r e d o n e m o d e l o f th e c r e a t i v e a c t. I n v e n t i o ni n d e s i g n i s , a m o n g o t h e r c o g n i t i v e c a p a b i li ti e s , c o n s i d e r e d t o b e i n f l u e n c e db y t h e b e h a v i o r a l m a s t e r y o f t h is p r o c e s s . M a n i p u l a t io n o f r e p r e s e n t a ti o n st h r o u g h s e q u e n c e s o f m u l t i p l e r e -r e p r e s e n t a ti o n s i s a k e y s t o n e o f th e c r e -a t i v e p r o c e s s w h i c h c a n r e s u l t in d e s i g n s o f u n e x p e c t e d d i v e r s i t y a n d n o v -e l t y . I t i s p a r t o f t h e p a r a d o x o f c r e a t i v i t y t h a t t h r o u g h r e - r e p r e s e n t a t i o n ,t h e n e w c a n b e m a d e f r o m t h e e x i s t i n g .O u r r e - r e p r e s e n t a t io n a l m o d e l o f r e -r e p r e s e n t a ti o n i n d e s i g n a p p e a r s t o p r o -v i d e o n e b a s i s f o r a f o r m a l t h e o r y o f c r e a t i v i t y . T h e f o l l o w i n g c o n c e p t s ,w h i c h h a v e e m e r g e d f r o m o u r e m p i r i c a l s tu d i e s, a r e r e l e v a n t to t h e f o r m a lm o d e l i n g o f c r e a t i v i t y .

- - t h e h u m a n a b i l i t y t o t r a n s f o r m i m p l i c i t k n o w l e d g e t o r e p r e s e n -t a t io n a l s t r u c t u r e e n a b l e s m o d i f i c a ti o n a n d c h a n g e ;- - t h e c a p a b i l i t y t o t r a n s f o r m k n o w l e d g e i n t o r e p r e s e n t a t i o n a l s t r u c -t u r e s u n d e r l i e s t h e a b i l i t y t o m a k e n o v e l m o d i f i c a t i o n s a n d c h a n g e sw i t h i n , o r t h r ough , t hos e r e p r e s e n t a t i ons ;- - t h e e s ta b l i s h m e n t o f t h e r i g h t r e p r e s e n t a t io n m a y b e c o n s i d e r e d t obe a c r e a t i ve a c t ;

C r e a t i v i t y c a n b e e x p l a i n e d i n s u c h a n a p p r o a c h b y d e m o n s t r a t i n g h o wd e s i g n s c a n b e a c c e s s e d a n d t r a n s f o r m e d i n n o v e l w a y s . F u r t h e r m o r e , c e r -

3 4 6 D e s i g n S t u d i e s V o l 1 8 N o 4 O c t o b e r 1 9 9 7


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t a in i n t er na l c ons t r a in t s o f a r e - re p r e se n t a t i on i n ou r m od e l m a y ne c e s s i t a t ethe a c c e s s ing o f a ne w l a ye r i n a no the r r e l e va n t de s ign . Th i s i s one o fm a n y f o r m s o f e x p l o r a t iv e p r o c e s s e s w h i c h a r e c o m m o n in c re a t iv i ty i nd e s i g n . T h e s e p h e n o m e n a c a n b e f o r m a l l y m o d e l e d w i t h i n a m u l t i - r e p -r e se n t a t iona l s c he m e o f de s ign a s r e - r e p r e se n t a ti on s t r a te gy .G iv e n tha t g r a ph ic r e - r e p re se n t a t i on i n de s ign i s suc h a n im por t a n t a nd a l lp e r v a s i v e p h e n o m e n o n , w e r e q u i r e m o r e e m p i r ic a l a n d t h e o r e ti c al w o r k i no r d e r to d e v e l o p t h e b a s i c c o n c e p t s s u c h a s a t a x o n o m y o f t y p es o f k n o w l -e dge s t r uctu r es , c on s t r a in t s o r c l a sse s o f s t ra t e g i es a n d m od i f i c a t i on ope r -a t i ons i n de s ign . L a c k ing th i s l e ve l o f ba s i c c onc e p t s , e ve n the de sc r ip t i ona nd a na ly s i s o f t he de s ign p r o toc o l s ha s be e n a d i f f i c u l t t a sk . I t i s a n t i c i -pa t e d t ha t t he se r e su l ts w i l l le a d t o a be t t e r unde r s t a nd ing o f hum a n de s ign -e r s a nd u l t im a te ly s t r e ng the n ou r a b i li t y t o de ve lo pm e n t t oo l s a nd m e thod sto suppo r t t he m .

cknowledgmentsT h i s r e s e a r c h w a s s u p p o r t e d b y t h e T e c h n i o n V P R F u n d . I w o u l d l i k eto e xp r e ss m y a pp r e c i a t i on o f t he s t im u la t i ng w or k o f the s tude n t s w h opa r t i cipa t e d i n t he g r a dua t e c ou r se i n A I in D e s ign . I w o u ld l i ke to pa r ti -c u l a r l y t h a n k A r c h i t e c t A m o s W a c h m a n w h o p r o v i d e d h i s w o r k t o i l l u s -t r at e ou r e m p i r i c a l s t udy in t h i s pa pe r. T he a s s i s t a nc e o f R . S ha r v i t a ndH . C a sa k in i s a l so a c know le dge d .

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oxman 1997 design by representation

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