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Pergamon Exper t Sys tem s With Appl icat ions , Vol . 10 , No. 3 /4 , pp . 481-48 6 , 1996C o p y r i g h t 1 9 96 E l s e v i e r S c ie n c e L t dPr inted in Great B r i ta in . A l l f igh ts r eserved0 9 5 7 - 4 1 7 4 / 9 6 1 5 . 0 0 + 0 . 0 0S0957-4174 96)00028-0

Visual Programm ing nvironm ent for H ybr id xpertSystems

YOSHIYUKI KOSEKI M [ D o m T A N A K A , Y A S U Y U K I M A E D A A N D Y U I C H I K OX K EC & C Research Laboratories,NEC Corporation,4-1-1 M iyazaki,Miyamae-ku,Kawasaki 216, Japan

A b s t r a c t - - T h i s pa per proposes an architecture fo r hyb r id exper t sys tem developm ent which combinesexper t problem-solv ing funct ions and o ther convent ional computat ional funct ions by v i sual program mingtechnology . The v i sual programm ing technique i s used b oth fo r task-specif ic know ledge representat ionand for proce dural program ming for connect ing fun ct ional components. In know ledge representat ion,know ledge i s v i sually represented in the for m of dec i s ion tables and d eci s ion t rees . In procedu ral v i sualprogram ming, each funct ion al objec t i s d i splayed as a box -shaped icon wi th access ible por t s w hich areconn ected by w ires on the graphic edi tor . Ba sed on the archi tec ture , an exper t sys tem shel l fo r thec lass if ication task , cal led HOL ON /VP DT) , i s incorpora ted in a v i sual program ming sys tem ca l ledHO LO N/VP . This pa per br ief ly d escr ibes the tool and i t s evaluat ion base d on some appl ication sys temsdeve loped wi th the tool. C opyr ight 199 6 Elsev ier Sc ience Ltd

1 . I N T R O D U C T I O NS I N C E T H E A D V E N T O F E X P E R T SY S T E M T E C H N O L O G Y i n t he1 9 70 s, a l a r g e n u m b e r o f e x p e r t sy s te m s h a v e b e e nd e p l o y e d . E x p e r i e n c e g a i n e d i n t h e d e v e l o p m e n t o f th o sesy s t e m s sh o w s t h a t t h e d e v e l o p m e n t o f g e n e r a l f u n c -t ions , such a s use r i n t e r face , da t abase access and s impled a t a m a n i p u l a t io n , r e q u i r e s m u c h m o r e e f f o r t th a n t h ed e v e l o p m e n t o f t h e p r o b l e m - so l v i n g p a r t . A l t h o u g hc o n v e n t i o n a l e x p e r t sy s t e m t o o l s p r o v i d e m a n y c o n v e n -i e n t f u n c t i o n s f o r d e v e l o p i n g t h e p r o b l e m - so l v i n g p a r t ,c o n s i d e r a b l e e f f o r t i s n e e d e d t o i m p l e m e n t t h o se

h y b r i d e x p e r t sy s t e m s , w h i c h c o m b i n e p r o b l e m -so l v i n g f u n c t i o n s w i t h c o n v e n t i o n a l c o m p u t a t i o n a lfunc t ions .

T h e o b j e c t i v e o f t h e r e se a r c h d e sc r i b e d i n t h i s p a p e r i st o p r o v i d e a n e x p e r t sy s t e m t o o l w h i c h e n a b l e s c o m -p u t e r - n o v i c e d o m a i n e x p e r t s t h e m se l v e s t o c r e a t e t h e i ro w n e x p e r t sy s t e m s . S i n c e d o m a i n e x p e r t s a r e u su a l l yn o t c o m p u t e r e x p e r t s , t h e t o o l sh o u l d p r o v i d e a ne n v i r o n m e n t f o r n o v i c e c o m p u t e r u se rs t o e a s i l y c r e a t e ah y b r i d sy s t e m .

I n r e c e n t y e a r s , a n u m b e r o f t o o l s h a v e b e e nd e v e l o p e d f o r k n o w l e d g e b a se d e v e l o p m e n t . H o w e v e r ,f e w a t t em p t s h a v e b e e n m a d e t o p r o v i d e a h y b r i d e x p e r ts y s t em d e v e l o p m e n t e n v i r o n m e n t. M o s t o f t h e c o n v e n -t io n a l t o o l s t a k e o n e o f t h e f o l l o w i n g a p p r o a c h e s :

p r o v i d e i n t e r f a c e w i t h o t h e r d e v e l o p m e n t sy s -t ems by func t ion ca l l l i b ra ry .

A l l o f t h e a p p r o a c h e s a r e s i m p l e e x t e n s i o n s o f c o n v e n -t iona l p rogramming t echniques . In any case ,p r o g r a m m i n g m u s t b e d o n e b y a n e m b e d d e d t e x t u a lp r o g r a m m i n g l a n g u a g e , w h i c h m a y b e L I S P o r Clanguage .

T h i s p a p e r i n t r o d u c e s a n o v e l e x p e r t sy s t e m t o o la rch i t ec ture , based on a v i sua l p rogramming t echnique .B a se d o n t h e a r c h i t e ct u r e , a v isu a l p r o g r a m m i n g sy s t e m ,n a m e d H O L O N / V E w a s d e v e lo p e d . T h i s t o o l i n c lu d e s ac l a ss i f i ca t ion t a sk-spec i f i c expe r t sys t em she l l ca l l edH O L O N / V P ( D T ) . T h i s p a p e r d e sc r i b e s t h e t o o l a n d i t se v a l u a t io n b a se d o n so m e a p p l i c a ti o n sy s t e m s d e v e l o p e dwi th the too l .

S e c t i o n 2 i n t r o d u c e s t h e g e n e r a l a r c h i t e c t u r e b a se d o na n o b j e c t - o r i e n t e d v i su a l p r o g r a m m i n g a p p r o a c h . T h evi sua l knowledge represen ta t ion of t he c l a ss i f i ca t iont a sk - o r ie n t e d p r o b l e m - so l v i n g t o o l i s d e sc r i b e d i n S e c -t i o n 3 . S e c t i o n 4 i l l u s t r a t e s t h e H O L O N / V P v i su a lp r o g r a m m i n g t o o l i n d e ta i l w i th so m e e x a m p l e s . S e c t i o n5 su m m a r i z e s t h e a d v a n t a g e s a n d d i s a d v a n t a g e s o f t h ea rch i t ec ture and presen t s an empi r i ca l eva lua t ion . Sec -t i o n 6 c o n c l u d e s b y p o i n t i n g o u t s e v e r a l a r e a s f o r f u r t h e rwork .

2 . G E N E R A L A R C H I T E C T U R E p r o v i d e c o n v e n t i o n a l c o m p u t a t i o n to o l s a r o u n d

t h e p r o b l e m - so l v i n g t o o l p r o v i d e p r o b l e m so l v e r o n a p r e - e x i s t e n t p r o -

g r a m d e v e l o p m e n t e n v i ro n m e n t

2.1. RequirementsT h e r e q u i r e m e n t s f o r a h y b r i d e x p e r t sy s t e m d e v e l o p -m e n t e n v i r o n m e n t a r e l i s te d b e l o w :

481

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4 8 2 E K o s e k i e t a l

(1) shor t lea rn ing time(2) min im a l deve lo pm ent e f for t(3) r easonable computa t iona l pe r formance .(4) h igh ma in ta inabi l i ty .

To mee t these r equi rements , a v isua l knowledge repre -sen ta t ion and a v isua l porogramming language a rein t roduced . Tha t r epresenta t ion and language a re eva l -ua ted accord ing to the abo ve requi rements in Sec t ion 5 .2 2 D e c l a r a t iv e a n d P r o c e d u r a l K n o w l e d g eExper t sys tems cons is t o f ma in ly two pa r t s . One i s theproblem-solv ing pa r t , which u t i l izes human exper tknowledge . Knowledge i s usua l ly r epresented dec la ra -t ive ly in ta sk- spec i f ic forms, such as ru le s , dec is ion t r ees ,dec is ion tab les and objec t r e la t ion graphs . The o the r pa r tcombines convent iona l func t ions , such a s ma in f lowdesc r ip tion , da tabase qu e ry and g raphica l use r in te r face .This pa r t i s usua l ly r epresented procedura l ly .2 .3 . O b j e c t - O r i e n t e d A r c h i t e c t u r eTo rea l ize hybr id exper t sys tems, which cons is t o fp r o b l em- s o lv in g c o mp o n e n t s a n d c o n v e n t i o n a l f u n c ti o ncomponents , we propose an objec t -or ien ted componentassembly a rch itec ture (F ig . 1 ). An exper t sys tem isassembled a s a se t o f ta sk- spec i f ic components g luedtoge the r . Those ta sk- spec i f ic comp onents a re provided asobjec ts , a s de f ined in the objec t -or ien ted pa rad igm.Those objec ts have in te rna l s ta te s and me thods tha t canbe ac t iva ted by o the r ob jec ts .2 4 Te x t u a l v s V i s u a l R e p r e s e n t a t i o nT h e a im o f e x p e r t s y s t e m t e c h n o lo g y i s t o p r o v id esof tware sys tems w i th exper t leve l in te l ligence . The keyto r ea l iz ing such a sys tem is to cap ture and u t i l ize theknowledge of expe r ienced human exper ts . In the ea r lydays , sepa ra t ing a dom ain- indepen dent in fe rence enginef r o m a d o ma in - d e p e n d e n t d e c l a r a t i v e k n o w le d g e b a s emade know ledge capture and u t i l izat ion eas ie r than w i thconvent iona l sof tware techno logy . However , the c rea t iona n d m a in t e n a n ce o f k n o w le d g e b a s es m u s t s t il l b e d o n eby spec ia l ly t r a ined technic ians ca l led knowledge engi -

neers.O u r g o a l i s t o p r o v id e a t o o l w h ic h a l l o w s t h e d o m a in

exper ts themse lves to c rea te knowledge bases , wi thoutt h e h e lp o f k n o w le d g e e n g in ee r s. S in c e d o m a in e x p e r t sa re usua l ly compute r novices , i t i s necessa ry to f i l l theg a p b e tw e e n c o mp u ta t i o n a l r e p r e s e n t a t i o n a n d h u ma nknowledge representa t ion . Some recent works u t i l izecomprehens ib le v isua l knowledge representa t ions , suchas ru le d iagrams, dec is ion t r ees and dec is ion tab les ,r a the r than tex tua l r epresenta tions .

This v isua l r epresenta t ion approach has been success-fu l in knowledge representa t ion for ta sk- spec i f ic too ls .For example , we c rea ted a c la ss i f ica t ion ta sk-or ien tedtool w hich u t i l izes v isua l know ledge representat ion . Thetool has been used in the unass is ted c rea t ion of prac t ica lknowledge bases by domain exper ts . I t s v isua l knowl-edge representa t ion i s b r ie f ly desc r ibed in the nextsec t ion . However , p rocedura l p rograms, o the r than theknowledge base , had to be wr i t ten in a procedura llanguage by programmers . There fore , to a l low domainexper ts to be ab le to make these procedura l p rogramsthemse lves , an iconic v isua l p rogramming too l wasdeve loped . This i s the second and ma in top ic of th ispape r and i t i s desc r ibed in the la te r sec t ions .

3 . V I S U A L K N O W L E D G E R E P R E S E N T A T I O NThis sec t ion desc r ibes the v isua l knowledg e representa -t ion , incorpora ted in the c la ss i f ica t ion problem-solv ingc o mp o n e n t , c a l l e d H O L O N /V P ( D T ) ( K o s e k i e t a l . ,1991; Sugiura e t a l . , 1993; Tanaka e t a l . , 1994) . I t isun ique in be ing based on a symbol ic dec is ion tab le anda graphica l dec is ion t r ee r epresenta t ion ra the r than ontex t ru le s . This r epresentat ion makes a m ore com prehen-s ib le know ledge base than do ru le s .

The c la ss i f ica t ion problem is to f ind appropr ia tec la sses for unknown concepts , g iven a se t o f a t t r ibu teva lue condi t ions for the concept . Cons ide r a s impleexam ple for a gr inde r se lec t ion problem in a hypothe t ica lf ac tory . The problem is to se lec t an appropr ia te gr ind e rfor a produc t accord ing to produc t r equi rements , such a smate r ia l f ea tures and requi red qua l i ty . An example ofgr inde r se lec t ion knowledge desc r ibed in dec is ion tab leform is show n in F ig . 2 . A dec is ion tab le r epresents a se t

I K o w l e d g e lUser interface I Base Database 1 Problem r , ~ ,e p o . S o l v e r r o oo d , /

[ presentation [ [ Tab les [ [o th er ystems I

Grinder-HGrinder-HGrinder-L

MaterialHard Sof t

xxx

Qual i tyHigh l . ow xx

F I G U R E 1 . G e n e r a l a r c h i te c t u r e. F I G U R E 2 . E x a m p l e d e c i s i o n t a b l e .

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Visual Programming Environment 48

Materia l ' ~ G r i n d e r - H ~i i L o - - ~ G r i n d e r _ L

F I GU R E 3 . E xam p l e d ec i s i o n t r ee .

o f p r o p o s i t io n a l l o g i c f u n c t i o n s e x p r e s se d i n D N F(di s junc t ive normal fo rm) . Thi s cons t ruc t a l lows theh a n d l i n g o f d i s j u n c t i v e c o n c e p t s w i t h m u l t i p l e - v a l u ea t tr i b u te s . T h i s k n o w l e d g e c a n b e d e sc r i b e d i n d e c i s i o nt ree form as show n in F ig . 3 .

T h e d e c i s i o n t a b l e r e p r e se n t a t i o n h a s t h r e e a d v a n -t ages . F i r s t , t he conten t i s comprehens ib l e to humans ,b e c a u se t a b l e s p r o v i d e m u l t i p l e v i e w s o f a k n o w l e d g eb a se . F o r e x a m p l e , w h e n g i v e n a c o n c e p t , a u se r c a neas i ly f ind which combina t ion of a t t r i bu tes g ives theconcept a s a conc lus ion . When a se t o f a t t r i bu tes i sg iven , we can a l so see which concept s a re se l ec t ed a s ac o n c l u s i o n . C o m p a r i n g m u l t i p l e c o n c e p t f u n c t i o n s i sa l so a n e a sy t a sk w i t h t h i s r e p r e se n t a t i o n . T h e s e c o n da d v a n t a g e i s t h a t i t c a n p r o v i d e a c o n c l u s i o n e v e n i fso m e o f t h e q u e r y a t t r i b u t e s a r e u n k n o w n . T h e t h i r dadvantage i s t ha t t abu la r represen ta t ion expl i c i t l y sepa r -a t es c o n t r o l k n o w l e d g e f r o m l o g i c a l k n o w l e d g e , w h e r e a sr u l e - b a se d r e p r e se n t a t i o n m i x e s t h e m b e c a u se t h e r u l eo r d e r i n g e x p r e s se s so m e c o n t r o l k n o w l e d g e .

A d i sadvantage of t he t abu la r represen ta t ion i s t ha t i tm a y b e c o m e sp a r se a n d t a k e u p t o o m u c h sp a c e . I n t h ew o r s t c a se , it r e q u i re s a n e x p o n e n t i a l n u m b e r o f r o w s t oimplement ce r t a in func t ions , such a s pa r i ty func t ions .H o w e v e r , t h i s s i t u a t i o n c a n b e a v o i d e d b y u s i n ghie ra rch ica l ly d iv ided t ab le s .

The sys t em cons i s t s o f a dec i s ion t ab le ed i to r , ad e c i s i o n tr e e e d i t o r a n d a p r o b l e m so lv e r . F i g u r e 4 sh o w s

F I GU R E 4 . E xam p l e d i sp l ay o f D T .

a n e x a m p l e d i sp l a y o f t h e se e d i to r s . T h e d e c i s i o n t a b l ee d i t o r a n d d e c i s i o n t r e e e d i t o r a l l o w d i r e c t m a n i p u l a t i o no f th e k n o w l e d g e b a se . A s w e l l a s a w h a t y o u s e e i swha t yo u ge t ed i t i ng func t ion , t he dec i s ion t ab le ed i to rp r o v i d e s s e v e r a l f u n c t io n s t o h e l p i n t h e c o n s t r u c t i o n o fk n o w l e d g e b a se s , n a m e l y s i m u l a t i o n , m i n i m i z a t i o n a n dver i f i ca t ion . The s imula t ion func t ion a l lows use rs t ov a l i d a t e a k n o w l e d g e b a se . T h e m i n i m i z a t i o n f u n c t i o nsh r in k s t h e s i z e o f t h e k n o w l e d g e b a se a n d i m p r o v e s i tsc o m p r e h e n s i b i l i ty . T h e v e r i fi c a ti o n f u n c t i o n c h e c k s t h ec o m p l e t e n e s s a n d r e d u n d a n c y .

T h e p r o b l e m so l v e r a c c o m p l i sh e s c l a s s i f i c a t i o n b ye x e c u t i n g a c a n d i d a t e d i s c r i m i n a t i o n c y c l e . I t d y n a m -ica l ly chooses an appropr i a t e a t t r i bu te to be acqui redaccord ing to the in forma t ion ga in pe r a t t r i bu te cos t . Theproblem so lve r can ca l l mul t ip l e t ab le s in a h i e ra rch ica lm a n n e r , so t h a t a l a r g e k n o w l e d g e b a se c a n b e i m p l e -m e n t e d a s a c o l l e c t i o n o f t a bl e s . T h e p r o b l e m so l v e r a l sop r o v i d e s a n i n t e r a c t i v e k n o w l e d g e a c q u i s i t i o n f u n c t i o nf o r r e f i n i n g k n o w l e d g e b a se s . U s i n g t h a t f u n c t i o n , t h eu se r c a n r e f i n e t h e k n o w l e d g e b a se b y g i v i n g a c r i t iq u eo f t h e f i n a l c o n c l u s i o n , w i t h o u t b e i n g a w a r e o f t h ein t e rna l r epresen ta t ion .

4 . V I S U A L P R O G R A M M I N GT h e p r e v i o u s s e c t io n i n t r o d u c e d v i su al k n o w l e d g e r e p r e -sen ta t ion for c l a ss i f i ca t ion problem so lv ing . A l thought h e sy s t e m p r o v i d e s h i g h p r o d u c t i v i t y a n d m a i n t a i n ab i l -i t y fo r c l a ss i f i ca t ion t a sks , i t i s no t app l i cab le to o the rt y p e s o f p r o g r a m m i n g , p a r t i c u la r l y p r o c e d u r a l o n e s. T h i sse c t io n d e sc r i b e s v i su a l p r o g r a m m i n g f o r t h e p r o c e d u r a lp a r t s a n d c o m p o n e n t c o n n e c t in g r o u t in e s .4 1 Iconic Program mingR e c e n t l y , r e s e a r c h o n v i su a l p r o g r a m m i n g h a s b e e na c t i v e a n d a v a r i e t y o f l a n g u a g e s h a v e b e e n i m p l e -m e n t e d . C o m m e r c i a l p r o d u c t s a r e a l r e a d y a v a i l a b l e f o rspec i f i c purpo ses , such a s s igna l p rocess ing , s imula t iona n d c o n t r o l sy s t e m s . S o m e sy s t e m s h a v e b e e n d e s i g n e df o r g e n e r a l - p u r p o se u se .

T h e m o s t p o p u l a r a r c h i t e c t u r e f o r r e c e n t v i su a lp r o g r a m m i n g l a n g u a g e s i s d a t a f l o w i c o n i c p r o g r a m -m i n g , su c h a s L a b V I E W , P r o g r a p h , S h o w a n d T e l l a n dVisaVis (Hansen , 1994) . An othe r i n t e res t ing a rch i t ec turei s based on a v i sua l ru l e p roduc t ion sys t em, such a sChemTra ins (Be l l & Lewis , 1993) .

T h e p r o g r a m m i n g l a n g u a g e d e sc r i b e d i n t h is p a p e r i sb a se d o n an i c o n a n d w i r e r e p r e se n ta t i o n , w h e r ep r o g r a m o b j e c t s a re d e sc r i b e d as b o x e s a n d c o n n e c t i o n samong them a re ind ica t ed by wi res . I t i s un ique in i t sc o m p u t a t i o n a l m o d e l t h a t i s n o t b a se d o n a d a t a f l o wm o d e l , w h i c h i s e m p l o y e d i n m o s t o f o t h e r i co n i c v i su a ll a n g u a g e s . R a t h e r t h a n h a v i n g o n e k i n d o f w i r e t or e p r e se n t d a t a f l o w s a m o n g p r o g r a m c o m p o n e n t s , thel a n g u a g e e m p l o y s t w o k i n d s o f w i r e s , o n e f o r c o n t r o l a n done f or da t a .

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4 8 4 Y K o s e k i e t a l

~ :~ i~ '? ~ ; ; i ~ : ~ ~ ' [ N a m e ]

; : : i~ , i a ; ~ ; ~ - J i : i: : i ~ ' ii } ~ i ~ ] R e p l yW i n d ~ |# ;N eF I G U R E 5 . S i m p l e a p p l i c a t i o n .

F i g u r e 5 sh o w s a s i m p l e v i su a l p r o g r a m f o r a s i m p l egraphica l use r i n t e r face (GUI) appl i ca t ion . Thi s examplei s to p r o v i d e t w o G U I w i n d o w s , w h o se f a c e d e s i g n s a r eshown on the r igh t s ide of t he f igure . P ress ing the" H e l l o " b u tt o n i n t h e t o p -r i gh t c o m e r w i n d o w n a m e d" H e l l o W i n d o w " , c a u se s t h e c o n t e n t s o f t h e t e x t - b o xb e l o w t o b e c o p i e d t o t h e t e x t - b o x o f t h e o t h e r w i n d o w ,c a l l e d " R e p l y W i n d o w " . P r e s s i n g t h e " B y e " b u t t o nte rmina tes the program.

To rea l i ze such a p rogram, the use r a t f i r s t uses theu se r i n t e r f a c e e d i t o r t o c r e a t e f a c e d e s i g n s o f t h e t w owindow s. In the figure , t he two win dow s on the r igh t s ideh a v e a l r e a d y b e e n c r e a t e d .

A f t e r c r e a t i n g t h o se w i n d o w s , t h e u se r d e f i n e s t h ep r o g r a m b e h a v i o r a s a " v i su a l p r o g r a m " b y u s i n g t h ev i su a l p r o g r a m e d i to r , w h i c h i s sh o w n o n t h e l e f t si d e o fthe f igure . Th ere a re th ree boxes and fo ur w i res . The l e f t -m o s t b o x i n t h e v i su a l p r o g r a m r e p r e se n t s t h e " H e l l oW i n d o w " , w h o se f a c e d e s i g n is sh o w n i n th e t o p r i g h t o ft h e f i g u r e . T h e s e c o n d b o x r e p r e se n t s t h e " R e p l yW i n d o w " , sh o w n i n t h e b o t t o m r i g h t . T h o se t w o b o x e sa r e c r e a t e d b y s i m p l y d r a g g i n g a n d d r o p p i n g t h e G U Iw i n d o w o b j e c t s i n to t h e v i su a l p r o g r a m m i n g e d i to r . T h et h i r d b o x i s t h e " e x i t " b o x , w h i c h r e p r e se n t s t h et e r m i n a ti n g f u n c t i o n . T h i s b o x i s p r o v i d e d b y t h e v i su a lp r o g r a m e d i t o r a s a d e f a u l t.

4 2 B o x esB o x e s r e p r e se n t f u n c t io n a l c o m p o n e n t s , su c h a s p r o b l e mso l v e r s , G U I w i n d o w s , d a t a b a se q u e r i e s a n d c o n t r o lf u n c t i o n s . A l t h o u g h t h e r e a r e m a n y k i n d s o f f u n c t i o n a lc o m p o n e n t s , t h e b o x f a c e d e s i g n s a r e u n i f i e d . A m o n gt h e m , G U I w i n d o w o b j e c t s a r e sp e c i a l o b j e c t s t h a t m a yc o n t a i n m u l t i p l e G U I o b j e c t s , su c h a s b u t t o n s a n d t e x tb o x e s .

E a c h b o x c o n s i s t s o f s e v e r a l a r e a s w i t h a c c e s s i b l epor t s . The re a re th ree k inds of a reas in a box: p rope r ty ,m e t h o d a n d c a l l b a c k f u n c ti o n . E a c h a r e a h a s p o r t s . T h e r ea r e t w o k i n d s o f p o r ts : c o n t r o l p o r t s , w h i c h a r e d i sp l a y e das t r i ang les , and da ta por t s , which a re d i sp l ayed asrec t angles .

Th e prope r ty a rea represen t s i n t e rna l s t a te da ta , whichm a y b e s e t o r r e a d t h r o u g h t h e p o r t s . F o r e x a m p l e , t h e" n a m e " t e x t - b o x e s i n b o t h w i n d o w s h a v e t h e " t e x t "

p r o p e r ty . M e t h o d i s th e p r o c e d u r e t o b e i n v o k e d b y o t h e ro b j e c ts . I n th e e x a m p l e , " R e p l y W i n d o w " h a s a m e t h o dc a l l e d " h i d e " , w h i c h i s c a l l e d b y t h e c a l lb a c k f u n c t i o n o ft h e " B y e " o b j e c t in t h e " H e l l o W i n d o w " . T h e c a l l b a c kfunc t ion i s pa r t i cu la r t o GUI ob jec t s ; i t gene ra t e s ane v e n t t o c a l l o t h e r m e t h o d s .

4 3 C o n tro l W i res a n d D a ta W i resT h e t w o k i n d s o f w i r e s a r e r e p r e se n t e d b y so l i d a n ddot t ed l i nes . So l id w i res show cont ro l f l ow , whereasd o t t e d w i r e s sh o w d a t a f l ow . S e r i a ll y c o n n e c t e d c o n t r o lw i r e s r e p r e se n t a s e r i es o f m e t h o d s t o b e i n v o k e d i n t h a torder .

F o r e x a m p l e , w h e n t h e " H e l l o " b u t to n o f th e " H e l l oW i n d o w " i s p r e s se d , th e t e x t p r o p e r t y o f th e " N a m e "t e x t b o x o f t h e " R e p l y W i n d o w " i s s e t t o t h e v a lu e o f t h e" N a m e " t e x t b o x o f t h e " H e l l o W i n d o w " . W h e n t h e" B y e " b u t t o n i s p re s se d , t h e " h i d e " m e t h o d o f t h e " R e p l yW i n d o w " i s c a l l e d a n d t h e w i n d o w b e c o m e s h i d d e n .T h e n t h e sp e c i a l f u n c t i o n " E x i t " i s i n v o k e d t o t e r m i n a t et h e p r o g r a m .

I n t h e c u r r e n t i m p l e m e n t a t i o n , th e v i su a l p r o g r a m i st rans l a t ed in to an in t e rna l sc r ip t l anguage . F igure 6sh o w s t h e i n t e r p r e t a ti o n o f t h e g i v e n e x a m p l e .

4 4 I mp l em en t i n g a n E x p er t S y s tem b y V i s u a lP r o g r a m m i n gT h e v i su a l p r o g r a m m i n g i s i n t e n d e d t o g l u e t o g e t h e rf u n c t i o n a l c o m p o n e n t s . T h e f i r s t s t e p i n b u i ld i n g a h y b r i de x p e r t sy s t e m i s t o i m p l e m e n t t h e p r o b l e m - so l v i n gf u n c t i o n b y p r o v i d i n g a k n o w l e d g e b a se a n d so m ep a r a m e t e r s . T h e u se r i n t e r f a c e is t h e n d e s i g n e d u s i n g t h eu se r i n t e r f a c e e d i t o r a n d c o n n e c t e d t o t h e p r o b l e m -so l v i n g c o m p o n e n t b y v i su a l p r o g ra m m i n g .

A l t h o u g h t h e i n t e n d e d u sa g e o f th e v i su a l p r o g r a m -m i n g i s a s " g l u e " , i t i s p o s s i b l e t o i m p l e m e n t a d e c i s i o nt ree -based c l a ss i f i ca t ion exper t sys t em en t i re ly by v i sua lp r o g r a m m i n g , w i t h o u t u s i n g t h e d e c i s i o n t r e e c o m p o -nent , a s desc r ibe d in the prev iou s sec t ion . F igure 7 showsa c o m p l e t e v i su a l p r o g r a m f o r t h e p r e v i o u s l y i n tr o d u c e dg r i n d e r s e l e c t io n sy s t e m . T h i s i s a l so a g o o d s a m p l e f o re v a l u a t in g t h e c o m p r e h e n s i b i l it y o f t h e v i su a l p r o g r a m -ming .

T h e r e su l t i s l e s s c o m p r e h e n s i b l e t h a n t h e i m p l e -menta t ion wi th a t a sk-spec i f i c t oo l , a s desc r ibed in the

Click callback method of Pu shButton(.HelloO.HelloO.)b e g i nt e m p i : = . H e l l o ) . N a m e 0 . t t ) ;. R e p l y 0 N a m 0 . t e x t 0 : = e m p I ;e n d ;C l i c k a l l b a c k e t h o d o f F u s h B u t t o n ( . H e l l o 0 . B y e 0 . )b e g i n

. R e p l y 0 . h i d e 0 ;e x i t 0 ;e n d ;

F I G U R E 6 . Sc ript representation of the example.

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FIGURE 7 . De c i s i on t re e Im p le me n ta t i on b y v i s u a l p rogra mm in g .

p r e v i o u s s e c t i o n , b e c a u s e t h e p r o b l e m - s o l v i n g k n o w l -edg e and implem enta t ion-spec i f i c rou t ines , such a s thew i n d o w c o n t r o l l i n g r o u t i n e s ( s h o w i n g a n d h i d i n g ) , a r em i x e d i n th e v i su a l p r o g r a m m i n g i m p l e m e n t a t i o n . H o w -e v e r , i t c a n b e o b s e r v e d t h a t t h e g e n e r a l f l o w o f t h edec i s ion t ree i s ma in ta ined in the v i sua l p rogram.

5 , E V A L U A T I O NS e v e r a l e x p e r i m e n t a l s y s te m s h a v e b e e n d e v e l o p e d w i t hthe desc r ibed v i sua l p rogram min g too l . I t i s s ti l l t oo ea r lyt o g i v e a c o n c r e t e e v a l u a t i o n w i t h o u t a n e x t e n s i v ee v a l u a t i o n e f f o r t. H o w e v e r , f r o m e x p e r i e n c e , t h e f o l l o w -i n g s i m p l e e v a l u a t i o n w i t h r e s p e c t t o t h e r e q u i r e m e n t sd e s c r i b e d e a r l y i n t h is p a p e r m a y b e g i v e n .

5 1 Short Learning TimeI n e x p e r i e n c e d u s e r s p r e f e r v i su a l p r o g r a m m i n g t o t e x t u a lp r o g r a m m i n g , b e c a u s e v i s u a l p r o g r a m i s r e l a t i v e l yi n t u i t i v e a n d c o m p r e h e n s i b l e . E s p e c i a l l y w i t h p r o p e rsample programs , v i sua l p rograms a re easy to s t a r t w i thf o r i n e x p e r i e n c e d u s e r s . H o w e v e r , f o r e x p e r i e n c e dp r o g r a m m e r s , w h o a r e a l r e a d y f a m i l i a r w i t h t e x t u a lp r o g r a m m i n g s t y l e , l e a r n i n g a n o t h e r c o m p l e t e l y d i f f e r -e n t p r o g r a m m i n g t y p e s e e m s t o b e a b u r d e n .

5 2 Less Development EffortA s a c o m p a r i s o n , a s m a l l sy s t e m w a s d e v e l o p e d b o t hw i t h t h e v i su a l p r o g r a m m i n g s y s t e m a n d a c o n v e n t i o n a lt e x t u a l p r o g r a m m i n g . B e f o r e th e e x p e r i m e n t , d ra w i n gv i s u a l p r o g r a m s w i t h m o u s e o p e r a t io n s w a s e x p e c t e d t oh a v e a m u c h h i g h e r p r o d u c t i v i ty th a n t e x t u a l p r o g r a m s .H o w e v e r , f o r c a s u a l p r o g r a m m e r s w h o a r e a l r e ad yc o m f o r t a b l e w i t h t y p i n g t e x t w i t h a k e y b o a r d , s y s t e m

d e v e l o p m e n t w i t h t h e v i s u a l p r o g r a m s y s t e m r e q u i r e da l m o s t s a m e a m o u n t o f t i m e a s d i d t h e t e x tu a l p r o g r a m -ming . Er rors due to mis typ ing a re l e s s f requent in v i sua lp r o g r a m m i n g , b e c a u s e t e x t t y p i n g i s s e l d o m n e c e s s a r ye x c e p t f o r v a r ia b l e n a m e s , m e t h o d n a m e s a n d c l a s sn a m e s i n v i su a l p r o g r a m m i n g .

5 3 Reasonable Com putational PerformanceBecause the v i sua l l anguage i s conver t ed in to in t e rna lt ex tua l l anguage in the cur ren t implementa t ion , t hec o m p u t a t i o n a l p e r f o r m a n c e i s c o m p a r a b l e t o c o n v e n -t iona l language , w i th neg l ig ib le ove rhe ad for conv ers ion .T h e l a n g u a g e c a n b e e i t h e r i n t e r p r e t ed o r c o m p i l e d w i t hr e a s o n a b l e p e r f o r m a n c e .

5 4 High MaintainabilityH i g h m a i n t a i n a b i l i t y i s c o n s i d e r e d t o b e t h e m o s ts ign i f i can t advantage of v i sua l l anguage . S ince thecont ro l f low i s v is ib l e , it is easy to unders t and the f low ofthe program a t a g l ance . Thi s g ives h igh ma in ta inab i l i t yt o t h e p r o g r a m , s i n c e t h e p r o g r a m i s r e a d a b l e a n dunders t andable a t a l a t e r t ime by a pe rson o the r than thedeve lope r . V i s ib l e da ta dependency wi th da ta l i nes a l soh e l p s t h e c o m p r e h e n s i b i l i t y o f t h e p r o g r a m . I n t e x t u a ll a n g u a g e , d a t a d e p e n d e n c i e s m u s t b e i n v e s t i g a t e d w i t ht h e h e l p o f p r o g r a m a n a l y z i n g t o o l s.

Inexp er i enced use rs a t f i r s t t end to encoun te r a l i nec o n g e s t i o n p r o b l e m , w h i c h m a y d e g r a d e m a i n t a i n a b i l -i t y . T h a t i s , w h e n b u i l d i n g a c o m p l e x s y s t e m , m a n yc o n t r o l l i n e s c r o s s e a c h o t h e r a n d m a k e t h e v i s u a lp r o g r a m i n c o m p r e h e n s i b l e . T o s o l v e t h i s p r o b l e m , t h es y s t e m p r o v i d e s a f u n c t i o n f o r s p l i t t i n g o n e b o x i n t omul t ip l e copies and pu t t ing them a t a rb i t ra ry p laces(Koik e e t a l ., 1995) . Thi s capabi l i t y a l lows program me rs

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to organize the program accord ing to the ma in cont ro lf low of the program, so tha t the l ine conges t ion problemma y b e a v o id ed .

6 . C O N C L U S I O NThis pape r desc r ibes an approach to us ing an objec t -or ien ted v isua l p rogramming technique for deve lopinghybr id exper t sys tems. The sys tem cons is t s o f seve ra lc o mp u ta t i o n a l c o mp o n e n t s , s o me o f w h ic h a r e t a s k -spec i f ic problem-solv ing too ls . Othe r pa r t s a reconvent iona l comput ing func t ions , such a s da tabaseaccess and graphica l use r in te r face . Visua l p rogram min gi s u s e d t o g lu e t h o s e c o m p u ta t io n a l c o mp o n e n t s t o g e th e rto ma k e u p a c o mp le t e s y s t em.

T h e s y s t e m h a s b e e n u s e d t o d e v e lo p s o me e x p e r i -menta l expe r t sys tems. Empir ica l eva lua t ion shows tha ti t s ma in ta inabi l i ty i s supe r ior to tex tua l p rogramminglanguages , because of i t s h igh comprehens ib i l i ty . How-ever , some problems remain to be so lved in fu turework .

The f i rs t p roblem enco unte red i s sca lab i l ity . S ince thecur ren t implementa t ion does not suppor t h ie ra rch ica lcons t ruc t ion of v isua l p rogramming, i t i s unable toc o n s t r u c t h ig h ly c o mp le x s y s t e ms b y v i s u a l p r o g r a m-min g a lone . The sys tem is be ing enhance d to incorpora teh ie ra rch ica l v isua l p rogramm ing.

Second, even though v isua l p rogramming re su l t s inh igh comprehens ib i l i ty and ma in ta inabi l i ty , i t r equi re sa lmost the same e f for t a s tex tua l p rogramming. We a recur ren t ly inves t iga t ing a way to incorpora te a PBD(programming by demonst ra t ion) approach to c rea t ingin i t ia l v isua l p rograms (Sass in , 1994; Sugui ra Kosek i ,1995).

Thi rd , in orde r to mee t the va r ious r equi rements ofexper t sys tem deve lopm ent , a va r ie ty of problem-solv ingobjec ts must be provided . Our fu ture p lan inc ludesdeve lopment of more ta sk-or ien ted problem so lve r s ,such as a com bina tor ia l op t imiza t ion problem so lve r.

Ac k now le dg e m e nts - -T he a u thor s e xpres s the i r a ppre c ia t ion to Ma sa -hiro Yamamoto, Takeshi Yoshimura and Masanobu Watanabe of theNEC Corpora t ion for g iv ing the m the oppor tuni ty to pur sue th i sresearch.

R E F E R E N C E SBell , B. Lewis , C. (1993). Chem Trains: a language for crea t ing

beha ving pictures . In Proc. of IEEE Symposium on VisualLanguages pp. 188-195.

Hansen, W. J. (Moderator) (1994). The 1994 visual languagescomparison. In Proc. of lEEE Symposium on Visual Languages pp.9 0 - 9 7 .

Koike , Y. , Maed a, Y. Koseki , Y. (1995) . Improvin g readabil i ty oficonic program s with m ult iple view ob jec t representa t ion. In Proc .of l lt h 1EEE Symposium on Visual Languages pp. 37-44 .

Koseki, Y., Nakakuki, Y. Tanaka, M. (1991). DT: A classificationproble m solver with tabular-knowled ge acquis it ion. In Proc. ThirdInt. Conf. on Tools or A1 pp. 156-163.

Sassin, M. (1994) . Creat ing user- intended programs with programm ingby de m ons t r a t ion . In Proc. of 1994 IEEE Symposium on VisualLanguages pp. 153-160.

Sugiura, A. Koseki, Y. (1995). Cre atin g datab ase queries bydemonstra t ion. In Proc. of l lt h IEEE Symposium on VisualLanguages pp. 164-171.

Sugiura, A., Riesenhuber, M. Ko seki, Y. (1993). Co mp rehen sibilityim prove m e nt of t a bular knowle dge ba se . In Proc. o f AAAI-93 pp.7 1 6 - 7 2 1 .

Tanaka, M. , Aoy ama, N. , Sugiura, A. Koseki , Y. (1994) . Integra t ionof mult iple kno wledge represe nta t ion for c lass if ica t ion problems. InProc. of Japan/Korea Joint Conferences on Expert Systems pp.1 5 9 - 1 6 4 .