Notes on the Vitality of Hypertext Systems

T he s e not e s a ddr e ss s ome t hought s on the i mpl e m e nt a t ion of s pa t ia l hype r t e xt s ys t e m s, pa r t i c ula r l y w i t h r e s pe c t t o de si gni ng pl a t f or ms t ha t r e ma i n bot h ma l l e a bl e a nd s ta bl e t hr ough pe r i ods of e xpe r i m e nt a t i on a nd r a dic a l c ha nge . T he c onc e pt s de s c r i be d he r e m a y w e l l be f a m i l i a r t o m y c oll e a gue s , but w oul d be di f f i c ult t o f i nd i n t he l i te r a t ur e . WHERE ARE THE HYPERTEXT SYSTEMS? A t t he f i r s t hype r t e xt c onf e r e nc e , i n N ove mbe r 1987, one c oul d s ta nd in t he de m ons t r a t i on a r e a a nd sur ve y a w ide r a nge of ne w hype r t e xt s ys t e m s. A f e w of t he se s yst e m s ( N LS , N ote c a r ds , T I E S , I nte r m e di a ) ha d be e n de pl a ye d f or a f e w ye a r s . O the r s ( i nc ludi ng S ymbol i c s D oc um e nt E xa m i ne r , H ype r C a r d, X a na du, G ui de , gI BI S , St or yspa c e , H ype r C a r d, S upe r B ook, N t ge r a i d, H ype r ga te ) w e r e m uc h younge r . W i th t he e xc e pt i on of NL S / A UG M E N T, t he ol d, e s tabl i she d s yst e m s w e r e a l l younge r t ha n V I KI [ 5] i s t oda y. T hi s i s s t r a nge . H ype r t e xt s yst e m s a r e muc h e a s i e r t o wr i t e t oda y t ha n t he y w e r e i n 1987. O ur c om put e r s a r e muc h f a s t e r , our l a ngua ge s a nd l i br a r i e s a r e gr e a tl y e nha nc e d, our unde r s t a ndi ng of s of t w a r e a r c hi t e c tur e , de s i gn, a nd de ve l opme nt ha ve a l l i m pr ove d dr a ma t i c a l l y. T he doc uve r se , t he n c ons i de r e d a pi pe dr e a m by e ve n i t s m os t s uppor t i ve s ym pa t hi z e r s , now i s r e a l . I n pa r t , i t ma y be na t ur a l tha t we w r it e f e w e r ne w s ys t e m s t oda y t ha n w e onc e di d. I n the 1980’ s , i f your r e s e a r c h pla ns r e qui r e d a hype r t e xt s ys t e m , you m os t l i ke ly ha d t o bui l d your ow n. T oda y, e xi s t ing t ool s a r e ubi qui tous , a nd a numbe r of r e se a r c h l a bor a t or i e s pos s e ss t ool s a nd f r a m e w or ks de ve l ope d ove r the c our s e of m a ny ye a r s . N e ve r t he l e s s , I f ind t he de a r t h of ne w s ys te m s st a r t li ng. I n pa r t , pe r ha ps t hi s s c a r c i t y r e f l e c t s a m i d90’ s r e s e a r c h c ons e ns us t ha t t he i nt e r e s t ing pa r t of t he hype r t e xt s ys t e m w a s i n the ba c ke nd or m i ddl e w a r e l a ye r ( c f . [ 7] , [ 6] , [ 8] ) . P e r ha ps ve t e r a ns of t he e a r ly de ve l opme nt e f f or ts r e me m be r t oo w e l l t he f i na nc i a l a nd hum a n c os t s of the e a r l y tool s a nd ha ve not ye t not i c e d t ha t t he e c onom y ha s c ha nge d1. A 1 In my Hypertext 2001 paper, “Card Shark and Thespis: exotic tools for hypertext narrative”, I describe two new hypertext systems, each of which was developed in the course of a few weeks. va r i e t y of s oc i e t a l , e c onom ic , a nd e t hnogr a phi c f a c t or s doubt l e ss pl a y a r ol e . B ut the c hi e f obs t a c l e , I s us pe c t , i s a f e a r t ha t ha s ha unt e d the hype r t e xt r e s e a r c h c omm uni ty f r om i t s e a r li e s t da ys t o t he pr e s e nt : t he f e a r t ha t a s yst e m w i ll gr ow r i gi d w it h a ge , f a de , a nd ult i m a te l y di s a ppe a r . VITALITY D e si gne r s of ne w hype r te xt sys t e ms ha ve a l wa ys be e n de e pl y c onc e r ne d a bout t he i r s ys te m s ’ de m i se . A t f i r st , t he c oll a ps e of the s ys t e m ’ s pl a t f or m w a s a n i ns ur m ount a bl e t hr e a t ; w he n t he la s t c om pute r t ha t c oul d r un your s ys t e m w a s de c om m i s si one d, s ur e l y your r e s e a r c h w a s doom e d. F or t una te l y, de ve lopm e nt s in s of t w a r e e m ula t i on ha ve r e nde r e d t hi s a nxie t y la r ge ly obsol e t e ; t he e nt ir e M a c i nt os h c omm uni ty s pe nt ha l f a de c a de on e m ul a t i on l i f e s uppor t w i thout pa r t ic ul a r l y not i c i ng. N or doe s s uc h l onge vi ty r e qui r e a s ubs t a nti a l us e r c om m uni t y. T he Fi na l F R E S S de mo ha s be e n a s ta r a tt r a c ti on a t s e v e r al pr e vi ous H ype r t e xt c onf e r e nc e s , a nd ye t D ur a nd r e por ts t ha t he ha s , onc e a ga i n, f ound a w a y t o r e vi ve F R E SS on ne w ha r dw a r e . T he c hi e f ha z a r d to t he s ur vi va l of a hype r t e xt pl a t f or m is not l os s of it s pla t f or m but r a t he r t he gr a dua l l os s of i ts v i tal i t y , i ts a bil i t y t o s uppor t c ha nge a nd e xpe r i m e nt a t ion. A vi t a l s ys t e m i s ope n t o i nnova ti on, s uppor t i ng s t r a nge i de a s a nd une xpe c te d a f f or da nc e s . Y oung s yst e m s a r e f i l l e d w i th vi ta l i t y. I n t i m e , m os t r e s e a r c h pl a t f or m s be c ome e nc r us t e d w i th obsol e t e c ode , i nc onve ni e nt a s s umpt i ons , obsc ur e opt i mi z a t ions . C ode gr ows ; a s i t gr ow s , i t be c om e s ha r de r to unde r s t a nd. Ea r l y a r c hit e c t ur a l de c i s ions ma y pl a gue the de s i gn, a nd ye t ma y be e m be dde d s o de e pl y t ha t c ha ngi ng t he m s e e ms i m pos s i bl e . The s c a r s of ol d e xpe r i m e nt s , ha s t y pa t c he s , c l e ve r ha c ks w hos e me a ni ng i s now a r c a ne , a l l gr a dua ll y a c c um ul a t e . E ve nt ua l ly, i t s e e ms e a si e s t t o s ta r t ove r , or t o c ha nge f ie l ds . TECHNIQUES FOR SUSTAINED VITALITY I n r e c e nt m ont hs , I ha ve be e n e nga ge d i n de s i gning H amps hi re , a f ounda t i on i nt e nde d t o s uppor t t w o di s t inc t l i ne s of hype r t e xt pl a tf or m de ve lopm e nt : S t or ys p ac e : a r e im pl e me nt a ti on of a c l a s s ic s yst e m f or na r r a t i ve , s pa t i a l hype r t e xt C e r e s : a s pa ti a l hype r te xt tool f or m a ki ng, a na lyz i ng, a nd s ha r i ng not e s S t or ys pa c e i s now 12 ye a r s ol d; we ’ d li ke Ha m ps hi r e to l a st a long ti m e be f or e i t ne e ds t o be r e bui l t . C e r e s a ddr e s s e s a n i m por t a nt pr obl e m dom a in t ha t r e ma i ns poor ly unde r s t ood; i t i s e xpe c t e d t o r e quir e unus ua ll y r a pi d c ha nge a nd e nha nc e me nt . B ot h s ys te m s mus t be s t a bl e a nd pol i s he d f r om i nc e pt i on. H ow m a y t hi s be done ? PLUGGABLE VIEWS S t or ys pa c e 1.x of f e r e d m ul t ipl e vi e w s of a s i ngle hype r t e xt . M a p, c ha r t s , out l ine s , a nd t r e e m a ps c ould e a c h be i nst a nt ia t e d, onc e or ma ny ti m e s , f oc us i ng on dif f e r e nt pa r t s of a doc um e nt. V i e w s w e r e c ons t r uc t e d by a F a c t or y f unc t i on, a nd e a c h vi e w i ns ta nc e a c t e d a s a n obse r ve r on a s ha r e d Hype r te xt st r uc tur e 2. Ea c h vi e w wa s t hus i nde pe nde nt , a nd ne w vie w s c oul d be a dde d wi t hout s ubs t a nti a l c ha nge s t o ot he r vi e ws or t o t he H ype r t e xt s t r uc t ur e . T he vi e ws t he m s e l ve s , how e ve r , t e nde d t o be f or mi da ble c hunks of c ode , s inc e e a c h vi e w ma na ge s i t s ow n l a yout , di spl a y, a nd i nt e r a c t i on. A good de a l of l ogi c , not a bl y m ous e ha ndl i ng, wa s r e pl i c a t e d a m ong vi e w s, m a ki ng it di f f i c ult t o e nf or c e c ons i s te nc y. A dding a ne w f e a t ur e – s t a t us r ol l ove r s , s a y, or c ont e xtua l me nus — r e qui r e d c ha nge s t o e a c h kind of vi e w. M a ki ng the s e c ha nge s w a s t e di ous a nd e r r or pr one . I n H a m pshi r e , pl ugga ble vi e w s de l e ga te m a ny of t he i r r e spons ibi l i ti e s to S t r a t e gy obj e c t s : L ayou t P ol i c y: r e s pons i bl e f or de c i di ng whi c h i t e m s a r e vi si bl e i n t he vi e w , a nd w he r e t he y a ppe a r on t he s c r e e n. D r aw i n gPol i c y: r e s pons i bl e f or dr a w ing a n i t e m i n a s pe c i f i e d a r e a of t he sc r e e n L i nk P ol ic y: r e s pons i bl e f or dr a w ing a ny l i nks t ha t m a y a ppe a r in t he vi e w T he s e s tr a t e gy obje c t s a r e int e r c ha nge a bl e , pe r mi t t i ng f a c i l e e xpe r i m e nt a t ion: not hi ng pr e ve nt s you f r om t a ki ng a pol i c y de si gne d f or a m a p a nd pl uggi ng it i nto a c ha r t or a l i s t . P oli c i e s c a n be f r e e l y m i xe d a nd m a t c he d. Thi s f r e e dom m a ke s i t e a s y t o pr ovi de e xtr a s e r vi c e s i n a w i de r r a nge of c ont e xt s; f or e xa mpl e , w he r e S t or ys pa c e 1.x pr ovi de d a m oda l , a l pha be t i c a l li st t o he l p us e r s l oc a t e a n i t e m by na m e , H a mps hi r e l e ts us s ha r e pr e se nt a ti on st yl e , c onte xt ua l m e nus , a nd m ode l e ss obse r ve r l ogic , a ll i nhe r i t e d f r om H ype r t e xt V i e w or a c qui r e d f r om a pl ugi n pol i c y a nd t he r e f or e ne a r l y f r e e . T o e ns ur e t ha t poli c i e s r e m a i n pl ugga ble , w e m us t r e s tr i c t hi dde n de pe nde nc i e s be tw e e n di f f e r e nt ki nds of pol i c ie s . I f poli c i e s us e e a c h ot he r ’ s s e r vi c e s , or r e l y on se r vi c e s f r om t he V i e ws t he y s e r ve , the n som e pol i c ie s w il l m a ke a s sum pt ions a bout t he i r pa r tne r s a nd we w i ll l ose 2 Storyspace 1,x for Macintosh was implemented in Pascal, and then reimplemented for Windows in C. For convenience, I use modern terms to describe structures and functions in these pre-object systems. Names of patterns conform to [3] unless otherwise specified, or thogona l i t y. T o pr e ve nt t hi s , pol i c ie s do not c om m uni c a te w i th e a c h ot he r , nor do t he y c onta i n ba c kpoi nt e r s t o t he V i e w t ha t us e s t he m . T his r e st r i c ti on is s ome t i m e s i nc onve ni e nt : f or e xa m pl e , the L a yout P ol i c y doe s n’ t know a nyt hi ng a bout t he dr a w i ng poli c y you pla n t o us e . T he D r a w i ngPol i c y, i n t ur n, m us t c ope w i th w ha t e ve r s c r e e n s pa c e it ’ s gi ve n a nd c a nnot ( a s i n O pe nD oc [ 1] ) ini t i a t e a ne goti a t i on f or a ddit i ona l s pa c e . But , i n c om pe ns a t ion, thi s im pove r i s he d c omm uni c a t i on pa t h a l so of f e r s de ve l opm e nta l i nde pe nde nc e : c ha nge s t o one ki nd of pol i c y ne ve r c ha nge t he ot he r s. B e c a us e de pe nde nc i e s a r e li m i t e d, w e a void m a ss i ve r e c ompi l a ti ons e ve n w he n unde r t a ki ng r a di c a l c ha nge s t o a pol i c y. I n pa r t i c ula r , the r e i s no di s inc e nti ve f or m a ki ng c ha nge s high i n t he pol i c y hi e r a r c hy or f or unde r t a ki ng r a di c a l e xpe r i m e nt s tha t mi ght ne e d t o be ba c ke d out 3. The di f f e r e nc e be t w e e n a n e xpe r im e nt t ha t t a ke s s e c onds to r e c om pi le a nd one t ha t r e quir e s mi nut e s i s s ubs ta nt i a l , e s pe c i a ll y w he n t r yi ng i nt e r e s t i ng e xpe r i m e nt s tha t mi ght not w or k. F a st e dit c ompi l e t e s t c yc l e s ke e p t he s ys te m young. A f ur t he r c ons e que nc e of t his s t r a t e gic a r c hi t e c t ur e i s t ha t i t e nf or c e s a s e pa r a ti on be t w e e n t he a bs tr a c t hype r t e xt N ode a nd t he gr a phi c obj e c t t ha t r e pr e s e nt s i t in a vi e w . N ode s c a nnot dr a w the m s e l ve s ; t he D r a w i ngPol i c y doe sn’ t si m pl y c a ll n o de > D ra w ( ... ) be c a us e t he node doe s n’ t know w ha t poli c y to f oll ow . I f t he r e a r e s e ve r a l c l a s se s of N ode s , e a c h of w hi c h m i ght ne e d t o be ha ndl e d s e pa r a te ly, t he l a yout a nd dr a w i ng pol ic i e s c a n be c om e c om pl e x. C ondi t iona l l ogi c m a y s uf f ic e i f onl y a f e w N ode c l a ss e s a r e ne e de d; i f ( n o d e> I s S p ec i a l () ) D r aw S p e ci a l ( no d e , ...) ; O ve r l oa di ng, or a V i s i tor a r r a nge m e nt [ 9] , ma y he l p i f t he c ondi t i ona l logi c be c ome s bur de nsom e . GIANT CLASSES AND OTHER CODE SMELLS P l ugga ble poli c i e s e m be dde d i n pl ugga ble vi e w s he l ps to ke e p t he vi e w hi e r a r c hy vi t a l , a nd t he vi e w hi e r a r c hy, a f te r a l l, i s w he r e s pa ti a l hype r te xt ha ppe ns . C or e c l a s s e s l i ke H ype r t e xt , L i nk, a nd N ode a r e e qua ll y ha r d t o ke e p vi t a l. F i r s t , the s e c l a s se s ha ve br oa d r e spons ibi l i ti e s , a nd so t he y t e nd t o a c quir e l a r ge int e r f a c e s . W or s e , ne a r l y e ve r yt hi ng i n a hype r t e xt s yst e m is l i ke l y to ne e d t o unde r s t a nd w ha t a H ype r t e xt i s a nd how a N ode or a L i nk w or ks . Cha nge s t o c or e c l a s se s t e nd t o be tr a um a t i c : a t be st , e ve r yt hi ng ne e ds t o be r e c om pi l e d; a t w or st , e ve r yt hi ng br e a ks . A bs t r a c t i ons i nhe r e nt i n t he c or e c l a s s e s be c om e i m pl i c i t a s s e r t i ons t hr oughout t he s yst e m : i f w e a s s um e t ha t a Li nk is a pa i r of r e f e r e nc e s t o N ode s , t he n c li e nt c l a s se s 3 If narrow communication channels are too confining, a blackboard might provide a useful alternative w i ll i nte r na li z e the a ss um pti on a nd i nt r oduc i ng m ult i he a de d l i nks l a t e r ma y pr ove inf e a si bl e [ 4] . T o ke e p c or e c l a s se s vit a l , t he y ne e d t o be s m a ll . T hi s m e a ns w e ne e d t o de l e ga te r e spons ibi l i ty s yst e m a ti c a l ly a nd t hor oughl y. W e m i ght be gi n, f or e xa m ple , by f a c tor i ng C ont e nt out of N ode , s o N ode s c a n de l e ga t e r e s pons i bi l i t y f or r e pr e s e nti ng, s e r i a l i z i ng, a nd c ha ngi ng t he ir c ont e nt t o a s e pa r a t e C onte nt obj e c t[ 2] . T hi s m e a ns, howe ve r , t ha t pe r va s i ve de pe nde nc y on a f e w bi g c l a ss e s is r e pl a c e d by w i de s pr e a d de pe nde nc y on m yr i a d sm a l l c l a s se s : T h eN o d e -> T e x tL e n g th ( )